Crystals

11 pages, 11226 KiB

Open AccessEditor’s ChoiceArticle

Transformation Mechanism of Undercooled Austenite and Deformation Behavior of a 1.2 GPa High-Strength Medium Mn Steel

by Ying Dong, Jiachen Xu, Lingming Meng, Qinghao Miao, Haobo Cui, Jiaxin Chen, Yu Du, Tao Liu, Qingdong Feng and Chengjun Zhu

Crystals 2025, 15(5), 487; https://doi.org/10.3390/cryst15050487 - 21 May 2025

Viewed by 393

Abstract

In this study, the phase transformation mechanism during the decomposition of undercooled austenite and its effect on the deformation behavior of a high-strength medium Mn steel were studied. The results indicate that the austenite formation during heating (α → γ) is a relatively [...] Read more.

In this study, the phase transformation mechanism during the decomposition of undercooled austenite and its effect on the deformation behavior of a high-strength medium Mn steel were studied. The results indicate that the austenite formation during heating (α → γ) is a relatively fast reaction. However, the transformation of undercooled prior austenite above the martensite start (M_s) temperature (γ → α) is difficult due to its high thermal stability. Only martensite transformation occurred during the final air-cooling stage following a 120-h isothermal treatment at 360 °C (slightly above M_s). The growth of martensite laths was limited by the boundaries of prior austenite grains and martensite packets. High-strength tensile properties were achieved, with a yield strength of 955 MPa, ultimate tensile strength of 1228 MPa, and total elongation of 11.6%. These properties result from the synergistic hardening effects of grain refinement, high-density lattice distortion, and an increased boundary length per unit area. The composition design with medium Mn content increased the processing window for high-strength martensite transformation, providing a theoretical basis for an energy-saving approach that depends on the decomposition transformation of undercooled austenite. Full article

(This article belongs to the Special Issue Advances in High Performance Metal Materials: Preparation, Properties, and Applications)

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13 pages, 3899 KiB

Open AccessEditor’s ChoiceArticle

Growth and Characterization of High Doping Concentration (2.1 at%) Ytterbium (Yb) Doped Lithium Niobate (LiNbO₃) Crystal: An Electrically Tunable Lasing Medium

by Kaicheng Wu, Mohammad Ahsanul Kabir, Kai-ting Chou and Shizhuo Yin

Crystals 2025, 15(5), 486; https://doi.org/10.3390/cryst15050486 - 21 May 2025

Viewed by 417

Abstract

In this paper, we report on the growth and characterization of high doping concentration (2.1 at%) ytterbium (Yb) doped lithium niobate (Yb:LiNbO₃) crystal. By using a slightly modified Czochralski method, we have successfully grown a usable size (2 mm × 2 [...] Read more.

In this paper, we report on the growth and characterization of high doping concentration (2.1 at%) ytterbium (Yb) doped lithium niobate (Yb:LiNbO₃) crystal. By using a slightly modified Czochralski method, we have successfully grown a usable size (2 mm × 2 mm × 30 mm) Yb:LiNbO₃ single crystal. We also conducted the energy-dispersive X-ray spectroscopy (EDS) and the X-ray diffraction (XRD) analyses, which experimentally confirm that the grown crystal is a Yb:LiNbO₃ single crystal. We also measured the absorption and emission spectra of the grown crystal. It was found out that there is a near-flat broad emission within a spectral range of 1004–1030 nm when excited at 980 nm for this high doping concentration Yb:LiNbO₃ crystal. Such a near-flat broad emission can be very useful for realizing high slope efficiency ultrafast (femtosecond) lasing in the Yb:LiNbO₃ crystal due to the low quantum defect of the Yb:LiNbO₃ crystal. We also investigated the electro-optic effect of the Yb:LiNbO₃. The experimental result confirms that the electro-optic (EO) effect of a highly doped (2.1 at%) lithium niobate crystal is close to the EO value of the pure lithium niobate. Thus, the highly doped Yb:LiNbO₃ crystal can still be an effective electrically tunable lasing medium. It can enable electrically tunable, high slope efficiency femtosecond lasing due to the combined features, including (1) a near flat broad emission spectrum at the spectral range of 1004–1030 nm, (2) a non-compromised electro-optic effect at high doping concentration Yb:LiNbO₃ crystal, and (3) a low quantum defect. Full article

(This article belongs to the Special Issue Rare Earths-Doped Materials (3rd Edition))

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14 pages, 5702 KiB

Open AccessEditor’s ChoiceArticle

Co_0.85Bi_0.15Fe_1.9X_0.1O₄ (X = Ce⁴⁺, Sm³⁺, Ho³⁺, and Er³⁺) Nanoparticles with Selective Anticancer Activity: A Structural and Morphological Approach

by Liza Saher, Adel Benali, Saoussen Haddad, Essebti Dhahri, Manuel P. F. Graça, Benilde F. O. Costa, Luisa A. Helguero and Artur M. S. Silva

Crystals 2025, 15(5), 482; https://doi.org/10.3390/cryst15050482 - 20 May 2025

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Abstract

In this work, we synthesized the Co_0.85Bi_0.15Fe_1.9X_0.1O₄ (X = Ce³⁺, Sm³⁺, Ho³⁺, and Er³⁺) nanoparticles via the auto-combustion method. The cell viability against two breast cancer [...] Read more.

In this work, we synthesized the Co_0.85Bi_0.15Fe_1.9X_0.1O₄ (X = Ce³⁺, Sm³⁺, Ho³⁺, and Er³⁺) nanoparticles via the auto-combustion method. The cell viability against two breast cancer cells (MDA-MB-231 and T-47D cells) and the PC3 prostate cancer cells were carefully analyzed and correlated with the structural parameters and particle size values as well as the chemical composition. The produced compounds’ morphological and structural characteristics were performed using scanning transmission microscopy (TEM) and X-ray Diffraction (XRD). For all compounds, the analyses of the XRD experimental data revealed a structurally reversed cubic spinel with space group Fd-3m. All of the compounds had crystallites smaller than 45 nm which concorded well with the particle size values deduced from TEM images. Co_0.85Bi_0.15Fe_1.9Ho_0.1O₄ nanoparticles induced a high mortality of breast and prostate cancer cells (MDA-MB-231, T-47D, and PC3) while the Co_0.85Bi_0.15Fe_1.9Sm_0.1O₄ compound (higher particle size) reduced almost 35% of MDA-MB-231 cancer cells. With very low cytotoxicity against normal human cells, the Co_0.85Bi_0.15Fe_1.9Ho_0.1O₄ nanoparticles play a significant role in the elimination of cancer cells. Full article

(This article belongs to the Special Issue Feature Papers on “Hybrid and Composite Crystalline Materials” 2025)

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16 pages, 5110 KiB

Open AccessEditor’s ChoiceArticle

Effects of Nitrogen Partial Pressure on the Microstructure and Mechanical Properties of High-Entropy Ti(C,N)-Based Gradient Cermets

by Yunhao Zhang, Houan Zhang, Dongxu Qiao, Xin Tao, Peng Xia and Siyong Gu

Crystals 2025, 15(5), 479; https://doi.org/10.3390/cryst15050479 - 19 May 2025

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Abstract

Titanium carbonitride (Ti(C,N))-based ceramics are widely utilized in mechanical machining, aerospace, and electronics, particularly in cutting tools and wear-resistant components. Two single-phase solid solution powders, non-high-entropy (Ti_0.83,W_0.07,Mo_0.04,Nb_0.03,Ta_0.04)(C_0.7,N_0.3) and high-entropy [...] Read more.

Titanium carbonitride (Ti(C,N))-based ceramics are widely utilized in mechanical machining, aerospace, and electronics, particularly in cutting tools and wear-resistant components. Two single-phase solid solution powders, non-high-entropy (Ti_0.83,W_0.07,Mo_0.04,Nb_0.03,Ta_0.04)(C_0.7,N_0.3) and high-entropy (Ti_0.6,W_0.1,Mo_0.1,Nb_0.1,Ta_0.1)(C_0.78,N_0.22), were synthesized via the carbothermal reduction–nitridation (CRN) method. Gradient-structured non-high-entropy (C-TiCN) and high-entropy (HE-TiCN) cermets were fabricated at 1450 °C by tailoring the nitrogen partial pressure in the range of 1–8 kPa. The effect of nitrogen partial pressure on the microstructure and mechanical properties of both materials was thoroughly analyzed. Both materials exhibited a three-layer gradient structure comprising a hard-phase-enriched surface layer, a binder-rich subsurface layer, and a chemically uniform core. Optimal performance was achieved at 4 kPa nitrogen partial pressure, at which both HE-TiCN and C-TiCN exhibited a desirable combination of surface hardness and fracture toughness. Compared with C-TiCN, HE-TiCN showed improvements in surface hardness and fracture toughness at subsurface and core regions (40 µm from the surface) by 4.9%, 11.2%, and 12.0%, respectively. The enhanced surface hardness of HE-TiCN is attributed to the significant lattice distortion and the synergistic effects associated with its high-entropy configuration. The improved toughness of the binder-rich layer is primarily ascribed to mechanisms such as crack deflection, crack branching, and the formation of tear ridges. These findings offer a promising strategy for developing gradient Ti(C,N)-based cermets with enhanced mechanical performance. Full article

(This article belongs to the Special Issue Structure and Properties of Ceramic Materials)

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10 pages, 2233 KiB

Open AccessEditor’s ChoiceArticle

Determination of the ²⁰⁷Pb Chemical Shift Tensor in Crocoite, PbCrO₄, Using Single-Crystal NMR Spectroscopy

by Sebastian Kläger, Otto E. O. Zeman and Thomas Bräuniger

Crystals 2025, 15(5), 480; https://doi.org/10.3390/cryst15050480 - 19 May 2025

Viewed by 297

Abstract

The full chemical shift tensor of ²⁰⁷Pb (spin

I = 1 / 2

) in the natural mineral crocoite, PbCrO₄, has been determined using single-crystal NMR spectroscopy at room temperature. The eigenvalues of the tensor in its principal axes system [...] Read more.

The full chemical shift tensor of ²⁰⁷Pb (spin

I = 1 / 2

) in the natural mineral crocoite, PbCrO₄, has been determined using single-crystal NMR spectroscopy at room temperature. The eigenvalues of the tensor in its principal axes system are

δ_{11} = - 2720 \pm 2

ppm,

δ_{22} = - 2319 \pm 4

ppm, and

δ_{33} = - 1830 \pm 5

ppm, resulting in an isotropic chemical shift of

δ_{iso} = - 2289 \pm 2

ppm. Additionally, these values were verified using a Herzfeld–Berger analysis of a polycrystalline sample under magic-angle spinning (MAS) conditions. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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28 pages, 7859 KiB

Open AccessEditor’s ChoiceArticle

Tailoring the Luminescence Properties of Strontium Aluminate Phosphors for Unique Smartphone Detectable Optical Tags

by Virginija Vitola, Milena Dile, Katrina Krizmane, Ernests Einbergs, Tinko Eftimov, Kristian Nikolov and Samia Fouzar

Crystals 2025, 15(5), 474; https://doi.org/10.3390/cryst15050474 - 17 May 2025

Viewed by 512

Abstract

In this work, a precursor-driven tailoring of strontium aluminate phosphors doped with Eu²⁺ and Dy³⁺ to generate unique, batch-specific luminescent signatures suitable for smartphone-detectable anti-counterfeiting tags was developed. A microwave-assisted hydrothermal synthesis approach was employed to explore the impact of a [...] Read more.

In this work, a precursor-driven tailoring of strontium aluminate phosphors doped with Eu²⁺ and Dy³⁺ to generate unique, batch-specific luminescent signatures suitable for smartphone-detectable anti-counterfeiting tags was developed. A microwave-assisted hydrothermal synthesis approach was employed to explore the impact of a wide range of alkaline hydroxide and carbonate precursors on the structure of strontium aluminate. The resulting materials exhibited distinct differences in crystalline phase composition, morphology, and trap depth distribution. A smartphone-based detection system was developed, enabling rapid identification of spectral fingerprints. This study demonstrates a viable strategy for embedding unique luminescent identifiers, offering a scalable solution for robust, low-cost anti-counterfeiting applications in both the spectral and the time domain. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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15 pages, 6028 KiB

Open AccessEditor’s ChoiceArticle

Crystalline Li-Ta-Oxychlorides with Lithium Superionic Conduction

by Hao-Tian Bao, Bo-Qun Cao and Gang-Qin Shao

Crystals 2025, 15(5), 475; https://doi.org/10.3390/cryst15050475 - 17 May 2025

Viewed by 569

Abstract

Nowadays, some amorphous and microcrystalline solid-state electrolytes (SSEs) with dual anions have attained high ionic conductivity and good compatibility with electrodes in all-solid-state lithium-ion batteries (ASSLIBs). In this work, crystalline SSEs of series A (Li_1+xTaO_1+xCl_4−x [...] Read more.

Nowadays, some amorphous and microcrystalline solid-state electrolytes (SSEs) with dual anions have attained high ionic conductivity and good compatibility with electrodes in all-solid-state lithium-ion batteries (ASSLIBs). In this work, crystalline SSEs of series A (Li_1+xTaO_1+xCl_4−x, −0.70 ≤ x ≤ 0.50) and B (LiTaO_2+yCl_2−2y, −1.22 ≤ y ≤ 0), having great application potential well over ambient temperatures, were prepared at 260–460 °C for 2–10 h using Li₂O, TaCl₅, and LiTaO₃ as the raw materials. The three-phase coexisting samples attained high σ values ranging from 5.20 to 7.35 mS cm⁻¹, which are among the reported high values of amorphous co-essential SSEs and other alloplasmatic crystalline ones. It is attributed to the synergistic effect of the polyanion trans-[O₂Cl₄] and cis-[O₄Cl₂] octahedra framework. Full article

(This article belongs to the Special Issue Synthesis, Structure and Application of Metal Halides)

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Graphical abstract

10 pages, 4485 KiB

Open AccessEditor’s ChoiceArticle

Surface Morphology of 6-Inch SiC Single Crystals in Solution Growth on Si-Face, C-Face and (

10 \bar{1} \bar{2}

) Plane

by Gangqiang Liang, Jiayi Kuang, Yilin Su and Yuan Liu

Crystals 2025, 15(5), 472; https://doi.org/10.3390/cryst15050472 - 16 May 2025

Viewed by 533

Abstract

For solution growth of 6-inch 4H-SiC bulk crystals, the surface step morphology of the crystals grown on Si-face, C-face and (

10 \bar{1} \bar{2}

) plane was systematically characterized by laser confocal microscopy. The 2D-nucleation and step-bunching were likely to occur [...] Read more.

For solution growth of 6-inch 4H-SiC bulk crystals, the surface step morphology of the crystals grown on Si-face, C-face and (

10 \bar{1} \bar{2}

) plane was systematically characterized by laser confocal microscopy. The 2D-nucleation and step-bunching were likely to occur during the 30 h growth on Si-face, leading to a rough surface with a macro-step height over 60 μm. By contrast, the step heights were maintained at 0.1–1 μm during 60 h growth on C-face, exhibiting good morphological stability for long-term growth. Moreover, the SiC crystal grown on the (

10 \bar{1} \bar{2}

) plane illustrated its excellence in producing fine steps, which is attributed to the smaller interfacial energy between the solution and (

10 \bar{1} \bar{2}

) substrates, suggesting that it offers a better approach to growing SiC single bulk crystals. Full article

(This article belongs to the Section Hybrid and Composite Crystalline Materials)

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24 pages, 100135 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Annealing Temperature on the Microstructure and Performance of Cold-Rolled High-Conductivity and High-Strength Steel

by Shuhai Ge, Xiaolong Zhao, Weilian Zhou, Xueming Xu, Xingchang Tang, Junqiang Ren, Jiahe Zhang and Yaoxian Yi

Crystals 2025, 15(5), 469; https://doi.org/10.3390/cryst15050469 - 16 May 2025

Viewed by 603

Abstract

Low-carbon micro-alloyed steel has become a wire material with great potential for further development due to its excellent comprehensive performance; however, there is still a lack of insight into the evolution of its electrical conductivity during annealing treatment after undergoing deformation. In this [...] Read more.

Low-carbon micro-alloyed steel has become a wire material with great potential for further development due to its excellent comprehensive performance; however, there is still a lack of insight into the evolution of its electrical conductivity during annealing treatment after undergoing deformation. In this present contribution, we systematically explored the intrinsic correlation between the microstructural characteristics (including grain size evolution, dislocation density change, etc.) and performance indexes of cold-rolled high-conductivity high-strength steels and their mechanisms, using the annealing temperature, a key process parameter, as a variable. Characterization methods were used to comprehensively investigate the variation rule of the electrical conductivity of low-carbon micro-alloyed steels containing Ti-Nb elements under different annealing temperatures, as well as their influencing factors. The results show that for the ultra-low-carbon steel (0.002% C), the dislocation density continuously decreases with the increasing annealing temperature. Both experimental steels underwent complete recrystallization at 600 °C, with grain growth increasing at higher temperatures (with ultra-low-carbon steel being finer than low-carbon steel (0.075% C)). Dislocation density in ultra-low-carbon steel decreased steadily, whereas low-carbon steel exhibited an initial decline followed by an increase due to carbon-rich precipitate pinning. The yield ratio decreased with the annealing temperature, with optimal performance being at 700 °C for ultra-low-carbon steel (lowest resistivity: 13.75 μΩ/cm) and 800 °C for low-carbon steel (best conductivity: 14.66 μΩ/cm). Yield strength in ultra-low-carbon steel was dominated by grain and precipitation strengthening, while low-carbon steel relied more on precipitation and solid solution strengthening. Resistivity analysis confirmed that controlled precipitate size enhances conductivity. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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28 pages, 11372 KiB

Open AccessEditor’s ChoiceArticle

Biological Control of Ca-Carbonate Crystal Microstructure and Texture: Adapting Crystal Morphology, Orientation, and Arrangement to Biomaterial Function

by Anna Sancho Vaquer, Erika Griesshaber, Juan Diego Castro-Claros, Carmen Salas, Xiaofei Yin, Antonio G. Checa and Wolfgang W. Schmahl

Crystals 2025, 15(5), 466; https://doi.org/10.3390/cryst15050466 - 15 May 2025

Viewed by 457

Abstract

The mineralized cover of chiton (Polyplacophora) soft tissue consists of aragonite, developed as shell-plates, girdle-scales, and girdle-spicules. This study characterizes crystallographic aspects of the girdle-spicules of the species Ischnochiton rissoi, Rhyssoplax olivacea, Acanthopleura vaillantii, and Acanthopleura spinosa. Spicule crystal [...] Read more.

The mineralized cover of chiton (Polyplacophora) soft tissue consists of aragonite, developed as shell-plates, girdle-scales, and girdle-spicules. This study characterizes crystallographic aspects of the girdle-spicules of the species Ischnochiton rissoi, Rhyssoplax olivacea, Acanthopleura vaillantii, and Acanthopleura spinosa. Spicule crystal arrangements and texture variations are described. Different misorientations between the spicule crystals are shown and are discussed with respect to the physical properties of the biomaterial. Characterization was performed with electron backscattered diffraction (EBSD), as well as with laser confocal and Field emission scanning electron microscopy (FE-SEM) imaging. All investigated species had porous spicules and distinct structural characteristics. Spicule crystal co-orientation strength was strongly increased for R. olivacea and I. rissoi, and it was almost random for A. vaillantii. R. olivacea, I. rissoi. A. spinosa spicule crystal texture was axial, whereas A. vaillantii spicule crystals were almost untextured. For all species investigated, spicule aragonite was twinned, as demonstrated with the strong 63°/64° peak in the misorientation angle distribution diagram, indicating a {110}-twin relationship. R. olivacea and I. rissoi spicules consisted of few twinned crystals and twin boundaries; A. vaillantii and A. spinosa spicules showed an abundance of twinned crystals and twin boundaries. We observed a difference in spicule dimension, morphology, arrangement on the girdle, and crystal organization for the investigated species, but always the generation of twinned aragonite. Full article

(This article belongs to the Section Mineralogical Crystallography and Biomineralization)

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15 pages, 3922 KiB

Open AccessEditor’s ChoiceArticle

First-Principles Investigation of the Effect of Vacancy Defects and Carbon Impurities on Thermal Conductivity of Uranium Mononitride (UN)

by Yulin Lan, Tianhao Rui, Zhuangzhuang Ma, Linyuan Lu, Yunhao Wang, Yang Yu, Mingxuan Deng, Tianxing Lan, Zhekang Zhao, Junjie Wang, Congyi Li and Haibin Zhang

Crystals 2025, 15(5), 459; https://doi.org/10.3390/cryst15050459 - 14 May 2025

Viewed by 360

Abstract

Uranium mononitride (UN) is a promising nuclear fuel with a high melting point, high thermal conductivity, and low coefficient of thermal expansion. Theoretical studies of UN can provide insights on its thermal transport mechanism, which is of great significance for the design and [...] Read more.

Uranium mononitride (UN) is a promising nuclear fuel with a high melting point, high thermal conductivity, and low coefficient of thermal expansion. Theoretical studies of UN can provide insights on its thermal transport mechanism, which is of great significance for the design and application of UN fuel. During the processing and operation, crystal defects and impurities, such as vacancies and carbon impurities, potentially arise in the nuclear fuel, which probably affect the thermomechanical properties of UN. To figure out the effect of vacancy defects and carbon impurities on the thermal conductivity of UN, density functional theory and Boltzmann transport theory are applied to conduct a theoretical investigation on the mechanical and thermal properties of ideal and defective UN. The calculated results show that in the case of UN with a U or N vacancy, both the lattice and electronic thermal conductivity are decreased, compared with the ideal case. With a carbon atom occupying the N site in the lattice, the electronic thermal conductivity is reduced but the lattice thermal conductivity is increased. Combining the results of lattice and electronic thermal conductivity, the total thermal conductivities of three defective states are lower than the ideal UN. The thermal conductivities of UN with a U vacancy (13.91 W/mK), N vacancy (15.36 W/mK), and a carbon atom occupying the N site (15.14 W/mK) are, respectively, reduced by 25.7%, 18.0%, and 19.2%, in comparison with ideal result (18.73 W/mK) at 1000 K. Full article

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15 pages, 3639 KiB

Open AccessEditor’s ChoiceArticle

Prediction of Temperature Factors in Proteins: Effect of Data Pre-Processing and Experimental Conditions

by Jure Pražnikar

Crystals 2025, 15(5), 455; https://doi.org/10.3390/cryst15050455 - 12 May 2025

Viewed by 403

Abstract

The B-factor or temperature factor is one of the most important parameters in addition to the atomic coordinates, and which is refined during the determination of the protein structure and stored in the Protein Data Bank. It reflects the uncertainty of the atomic [...] Read more.

The B-factor or temperature factor is one of the most important parameters in addition to the atomic coordinates, and which is refined during the determination of the protein structure and stored in the Protein Data Bank. It reflects the uncertainty of the atomic positions and is closely linked to atomic flexibility. By using graphlet degree vectors as feature descriptors in a linear model—together with appropriate data transformation and consideration of various experimental factors—the model provides better prediction results. For example, the inclusion of crystal contacts in the linear model significantly improves the prediction accuracy. Since the distributions of the B-factors typically follow an inverse gamma distribution, applying a logarithmic transformation further improves the performance of the model. It has also been shown that large ligands, such as those found in protein–DNA complexes, have a significant impact on the quality of the prediction. A linear model based on graphlet degree vectors proves to be effective not only for the prediction of B-factors and the validation of deposited protein structures but also for the qualitative estimation of root-mean-square fluctuations derived from molecular dynamics. Full article

(This article belongs to the Section Macromolecular Crystals)

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15 pages, 4851 KiB

Open AccessEditor’s ChoiceArticle

Shape-Engineering and Mechanism Investigation of AgCl Microcrystals

by Chunli Cai, Qian Wang, Changsheng Yin, Xuhuan Li, Rong Yang, Xiaodong Shen and Wenbo Xin

Crystals 2025, 15(5), 451; https://doi.org/10.3390/cryst15050451 - 10 May 2025

Cited by 1 | Viewed by 331

Abstract

AgCl microcrystals are used in visible light photocatalysis. However, their properties depend strongly on the morphology of the crystals and the degree of exposure of the crystal planes. Despite extensive research conducted on the synthesis of AgCl microcrystals, the majority of existing studies [...] Read more.

AgCl microcrystals are used in visible light photocatalysis. However, their properties depend strongly on the morphology of the crystals and the degree of exposure of the crystal planes. Despite extensive research conducted on the synthesis of AgCl microcrystals, the majority of existing studies have focused on the stable growth of crystals. The role of Cl⁻ ions concentration as a key factor controlling the microcrystals morphology has not been fully explored, which limits the precise tuning of the morphology of AgCl microcrystals. In this study, AgCl microcrystals with controllable morphology are successfully synthesized by a facile solvothermal method. During the preparation process, ethylene glycol (EG) is utilized as a solvent, while polyvinylpyrrolidone (PVP) is employed as a surfactant. We systematically investigate the etching mechanism of AgCl microcrystals by analyzing the effect of sodium chloride (NaCl) concentration on their morphology. This investigation involves the integration of diverse characterization methods, including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and geometrical struc-ture analysis. The results demonstrate that Cl⁻ functions as both a surfactant, thereby promoting the nucleation of cubic microcrystals, and as an etchant, selectively etching the crystal surface. The order of selective etching on the crystal surface follows (100) planes > (110) planes > (111) planes. Based on this new mechanism, AgCl microcrystals with various morphologies, such as cube, octopod and dendrite, are successfully prepared, which provides a new idea for the precise design of noble metal halide microcrystals. Full article

(This article belongs to the Section Crystal Engineering)

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15 pages, 4412 KiB

Open AccessEditor’s ChoiceArticle

Evolution of Phonon Spectral Energy Density in Superlattice Structures

by Milad Nasiri and Yan Wang

Crystals 2025, 15(5), 446; https://doi.org/10.3390/cryst15050446 - 9 May 2025

Cited by 1 | Viewed by 522

Abstract

Superlattices are a distinctive class of artificial nanostructures formed by the periodic stacking of two or more materials. The high density of interfaces in these structures often gives rise to exotic physical properties. In the context of thermal transport, it is well established [...] Read more.

Superlattices are a distinctive class of artificial nanostructures formed by the periodic stacking of two or more materials. The high density of interfaces in these structures often gives rise to exotic physical properties. In the context of thermal transport, it is well established that such interfaces can significantly scatter particle-like phonons while also inducing constructive or destructive interference in wave-like phonons, depending on the relationship between the phonons’ coherence lengths and the superlattice’s period thickness. In this work, we systematically investigate the effect of temperature on the spectral energy density of phonon modes in superlattices. Additionally, we examine how variations in superlattice period thickness influence phonon lifetimes and energy density. Our findings provide critical insights into the spectral phonon properties of superlattices, particularly in terms of their coherence and lifetimes. Full article

(This article belongs to the Special Issue Metamaterials and Their Devices, Second Edition)

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16 pages, 7322 KiB

Open AccessEditor’s ChoiceArticle

Structural Study of Thermostable Ginsenoside β-Glucosidase from Caldicellulosiruptor bescii

by Jung-Min Choi

Crystals 2025, 15(5), 447; https://doi.org/10.3390/cryst15050447 - 9 May 2025

Viewed by 474

Abstract

Protopanaxadiol-type ginsenosides, the major bioactive components of Panax ginseng, exhibit diverse pharmacological activities, but suffer from low oral bioavailability due to poor water solubility and membrane permeability. Enzymatic deglycosylation has emerged as an effective strategy to enhance their therapeutic potential; however, most [...] Read more.

Protopanaxadiol-type ginsenosides, the major bioactive components of Panax ginseng, exhibit diverse pharmacological activities, but suffer from low oral bioavailability due to poor water solubility and membrane permeability. Enzymatic deglycosylation has emerged as an effective strategy to enhance their therapeutic potential; however, most glucosidases lack sufficient thermostability for industrial applications. A β-glucosidase from the thermophilic bacterium Caldicellulosiruptor bescii (CbBGL) has demonstrated efficient conversion of major ginsenosides into compound K at elevated temperatures. In this study, the high-resolution crystal structure of CbBGL was determined at 1.9 Å. Structural analysis revealed that CbBGL adopts a classical (α/β)₈ TIM barrel fold and functions as a homodimer. Comparative studies with other glucosidases highlighted structural features contributing to its thermostability, including moderate B-factor distribution and a limited hydrogen bond network. Docking analyses revealed a narrow, inverted conical substrate-binding cleft, which imposes specific binding orientations and underlies the enzyme’s stepwise deglycosylation mechanism. These insights provide a structural basis for CbBGL’s thermal resilience and substrate specificity, offering a valuable platform for the rational engineering of glucosidases in ginsenoside bioconversion processes. Full article

(This article belongs to the Special Issue Crystallography of Enzymes)

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11 pages, 2623 KiB

Open AccessEditor’s ChoiceArticle

Structural Analysis of PlyKp104, a Novel Phage Endoysin

by Jung-Min Choi

Crystals 2025, 15(5), 448; https://doi.org/10.3390/cryst15050448 - 9 May 2025

Viewed by 345

Abstract

Antibiotic resistance has emerged as a critical global public health challenge, prompting increased interest in non-antibiotic antimicrobial strategies such as bacteriophage-derived endolysins. Although endolysins possess strong lytic potential, their application to Gram-negative bacteria remains limited due to the outer membrane barrier. PlyKp104 is [...] Read more.

Antibiotic resistance has emerged as a critical global public health challenge, prompting increased interest in non-antibiotic antimicrobial strategies such as bacteriophage-derived endolysins. Although endolysins possess strong lytic potential, their application to Gram-negative bacteria remains limited due to the outer membrane barrier. PlyKp104 is a recently identified phage-derived endolysin that exhibits lytic activity against Gram-negative bacteria without the aid of membrane permeabilizers. In this study, the crystal structure of PlyKp104 was determined at a resolution of 1.85 Å. PlyKp104 consists solely of a catalytic SLT domain, and structure-based analysis revealed a putative active site and key structural features associated with substrate binding. Comparative analysis with homologous structures suggested that PlyKp104 belongs to lytic transglycosylase family 1. B-factor analysis and hydrophobic interaction mapping indicated that the domain exhibits high structural stability, supported by conserved hydrophobic residues clustered in motifs I and II. During structure determination, an unidentified electron density was consistently observed near a neutral, hydrophobic surface region. Its shape and environment suggest the presence of a lipid-like molecule, implying a potential lipid-binding site. These findings provide structural insight into PlyKp104 and contribute to the understanding of endolysin mechanisms against Gram-negative bacteria, with implications for future protein engineering efforts. Full article

(This article belongs to the Special Issue Crystallography of Enzymes)

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22 pages, 6877 KiB

Open AccessEditor’s ChoiceArticle

Inspection of Bulk Crystals for Quality Control in Crystal Growth: Assessment of High-Energy X-Ray Transmission Topography and Back-Reflection Topography Pinpointed for Physical Vapor Transport-Grown Aluminum Nitride

by Roland Weingärtner, Boris Epelbaum, Andreas Lesnik, Gleb Lukin, Stephan Müller, Leon Schiller, Elke Meissner, Matthias Weisser and Sven Besendörfer

Crystals 2025, 15(5), 449; https://doi.org/10.3390/cryst15050449 - 9 May 2025

Viewed by 522

Abstract

A comprehensive X-ray topography analysis of two selected aluminum nitride (AlN) bulk crystals is presented. We compare surface inspection X-ray topography in back-reflection geometry with high-energy transmission topography in the Lang and Laue configuration using the monochromatic K_α1 excitation wavelength of copper, [...] Read more.

A comprehensive X-ray topography analysis of two selected aluminum nitride (AlN) bulk crystals is presented. We compare surface inspection X-ray topography in back-reflection geometry with high-energy transmission topography in the Lang and Laue configuration using the monochromatic K_α1 excitation wavelength of copper, silver, and tungsten, respectively. A detailed comparison of the results allows the assessment of both the high- and low-energy X-ray topography methods with respect to performance and structural information, giving essential feedback for crystal growth. This is demonstrated for two selected AlN freestanding faceted crystals up to 8 mm in thickness grown in all directions using the physical vapor transport (PVT) method. Structural defects of all facets of the crystals are determined using the X-ray topography in back-reflection geometry. The mean threading dislocation densities are 480 ± 30 cm⁻² for both crystals of either the Al- or N-face. Clustering of dislocations could be observed. The m-facets show the presence of basal plane dislocations and their accumulation as clusters. The integral transmission topographs of the

10 \bar{1} 0

(m-plane) reflection family show that basal plane dislocations of the screw type in

\frac{1}{3} ⟨\bar{1} 2 \bar{1} 0⟩

directions decorate threading dislocation clusters. Three-dimensional section transmission topography reveals that the basal plane dislocation clusters mainly originate at the seed boundary and propagate in the

\frac{1}{3} ⟨\bar{1} 2 \bar{1} 0⟩

direction along the growth front. In newly laterally grown material, the Borrmann effect has been observed for the first time in PVT-grown bulk AlN, indicating very high structural perfection of the crystalline material in this region. This agrees with a low mean FWHM of 10.6 arcsec of the

10 \bar{1} 0

reflection determined through focused high-energy Laue transmission mappings. The latter method also opens the analysis of the

∆ 2 θ

-shift correlated to the residual stress distribution inside the bulk crystal, which is dominated by dislocation clusters. Contrary to Lang transmission topography, the de-focused high-energy Laue transmission penetrates the 8 mm-thick crystal enabling a defect analysis in the bulk. Full article

(This article belongs to the Section Crystal Engineering)

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13 pages, 2056 KiB

Open AccessEditor’s ChoiceArticle

Finding Crystal Orientations in Uniplanar Textures

by Josef Simbrunner, Fabian Gasser, Sanjay John, Ingo Salzmann and Roland Resel

Crystals 2025, 15(5), 443; https://doi.org/10.3390/cryst15050443 - 8 May 2025

Viewed by 361

Abstract

The crystallization of molecular materials on isotropic substrates typically results in a so-called fiber or uniplanar texture that comprises crystallites that share a common fiber axis perpendicular to the substrate surface, but that are azimuthally randomly oriented. The crystallographic characterization of such films [...] Read more.

The crystallization of molecular materials on isotropic substrates typically results in a so-called fiber or uniplanar texture that comprises crystallites that share a common fiber axis perpendicular to the substrate surface, but that are azimuthally randomly oriented. The crystallographic characterization of such films is commonly performed by grazing-incidence X-ray diffraction. Thereby, two-dimensional reciprocal space maps are obtained that incorporate the in-plane component q_xy and the out-of-plane component q_z for each diffraction peak. The exact position of each diffraction peak depends on the crystallographic lattice and on the orientation of the unit cell relative to the substrate surface. The unit cell orientation can be characterized either by two rotation angles or by the Miller indices of the crystallographic plane (contact plane) parallel to the substrate surface. Equations are derived that allow the calculation of these orientation parameters and describe the relations between them. Depending on the crystallographic system of the underlying unit cell and its contact plane, manifold possible orientations may exist due to the multiplicity of planes contributing to the same reflections. Examples based on molecular crystals of pentacenequinone, diindenoperylene, and binaphthalene are discussed, which are illustrative examples comprising triclinic, monoclinic, and tetragonal unit cells having two, four, and sixteen possible crystal orientations, respectively. Full article

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15 pages, 4952 KiB

Open AccessEditor’s ChoiceArticle

Optimized Breakdown Strength and Crystal Structure for Boosting the Energy Storage Performance of Niobate-Based Glass Ceramics via a B-Site Substitution Strategy

by Kexin Gao, Fei Shang, Yaoyi Qin and Guohua Chen

Crystals 2025, 15(5), 444; https://doi.org/10.3390/cryst15050444 - 8 May 2025

Cited by 1 | Viewed by 464

Abstract

Based on the B-site modification strategy, excellent energy storage properties were achieved in this work by substituting Nb with Ta of the same valence in niobate-based glass ceramics. Ta substitution was found to lead to the transformation of crystal structures, and the space [...] Read more.

Based on the B-site modification strategy, excellent energy storage properties were achieved in this work by substituting Nb with Ta of the same valence in niobate-based glass ceramics. Ta substitution was found to lead to the transformation of crystal structures, and the space point group evolved from the non-centrosymmetric P4bm to the centrosymmetric P4/mbm, resulting in a transition from relaxor ferroelectric to paraelectric glass ceramics. Furthermore, the addition of Ta led to a significant decrease in grain size and interfacial activation energy, as well as an increase in the optical band gap, resulting in a dramatic increase in BDS from 800 kV/cm to 1300 kV/cm. The KBSN-4.0mol%Ta₂O₅ glass ceramic exhibited optimal energy storage properties, including a discharge energy density of ~5.62 J/cm³ and a superfast discharge rate of ~9.7 ns, resulting in an ultrahigh discharge power density of about ~1296.9 MW/cm³ at 1300 kV/cm. Furthermore, this KBSN-Ta glass ceramic also displayed good thermal stability over a temperature range of 20–120 °C, with the W_d decreasing by 9.0% at 600 kV/cm. B-site modification engineering in glass ceramics has proved to be an important way to effectively optimize energy storage performance. Full article

(This article belongs to the Special Issue Advances in Glass-Ceramics)

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12 pages, 2166 KiB

Open AccessEditor’s ChoiceArticle

¹¹⁹Sn Element-Specific Phonon Density of States of BaSnO₃

by Alexey Rulev, Hongxin Wang, Selma Erat, Murat Aycibin, Daniel Rentsch, Vladimir Pomjakushin, Stephen P. Cramer, Qianli Chen, Nobumoto Nagasawa, Yoshitaka Yoda and Artur Braun

Crystals 2025, 15(5), 440; https://doi.org/10.3390/cryst15050440 - 5 May 2025

Viewed by 342

Abstract

Vibration spectroscopy is routinely used in analytical chemistry for molecular speciation. Less common is its use in studying the dynamics of reaction and transport processes. A shortcoming of vibration spectroscopies is that they are not inherently specific to chemical elements. Progress in synchrotron [...] Read more.

Vibration spectroscopy is routinely used in analytical chemistry for molecular speciation. Less common is its use in studying the dynamics of reaction and transport processes. A shortcoming of vibration spectroscopies is that they are not inherently specific to chemical elements. Progress in synchrotron radiation-based X-ray technology has developed nuclear resonance vibration spectroscopy (NRVS), which can be used to produce element-specific vibration spectra and partial vibrational density of states (PVDOS), provided the material under investigation contains a Mössbauer-active element. While the method has been recently used successfully for protein spectroscopy, fewer studies have been conducted for condensed matter. We have employed NRVS on the BaSnO₃ perovskite structure, which is a model compound for ceramic proton conductors in intermediate temperature fuel cells. Since we used ¹¹⁹Sn as a Mössbauer isotope, the derived experimental PVDOS is specific to the element Sn in BaSnO₃. We show how this phonon DOS is used as an experimental anchor for the interpretation of the DFT-calculated PVDOS of BaSnO₃. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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10 pages, 4289 KiB

Open AccessEditor’s ChoiceArticle

Theoretical Investigation of Chromium Separation from Chromates Through Photon–Phonon Resonant Absorption

by Mingyan Xie, Haoxin Ren, Yuanda Huang, Peilin Li, Yining Li, Yawen Li, Yuqi Xia and Peng Zhang

Crystals 2025, 15(5), 437; https://doi.org/10.3390/cryst15050437 - 3 May 2025

Cited by 1 | Viewed by 536

Abstract

Chromium (Cr) is a vital metal utilized in materials physics, healthcare, and various other domains. In this study, we propose an eco-friendly method for separating Cr from potassium chromate (K₂CrO₄) based on photon–phonon resonance absorption theory. Using first-principles density [...] Read more.

Chromium (Cr) is a vital metal utilized in materials physics, healthcare, and various other domains. In this study, we propose an eco-friendly method for separating Cr from potassium chromate (K₂CrO₄) based on photon–phonon resonance absorption theory. Using first-principles density functional theory calculations, we obtained the Raman and infrared spectra of K₂CrO₄ and assigned the vibrational modes to the peaks observed in the experimental spectra. We confirmed that the strongest infrared absorption peak corresponds to the Cr-O bond stretching vibration theoretically located at 931 cm⁻¹. We propose employing a high-power terahertz laser at this resonant frequency for photothermal energy transfer. This approach is expected to enhance the efficiency of separating Cr from K₂CrO₄. Experimental investigations are expected in the future. Full article

(This article belongs to the Special Issue Laser–Material Interaction: Principles, Phenomena, and Applications)

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9 pages, 1803 KiB

Open AccessEditor’s ChoiceArticle

Inelastic Electron Tunneling Spectroscopy of Aryl Alkane Molecular Junction Devices with Graphene Electrodes

by Hyunwook Song

Crystals 2025, 15(5), 433; https://doi.org/10.3390/cryst15050433 - 1 May 2025

Viewed by 350

Abstract

We present a comprehensive vibrational spectroscopic analysis of vertical molecular junction devices constructed using single-layer graphene electrodes separated by an aryl alkane monolayer. In this work, inelastic electron tunneling spectroscopy (IETS) is employed to probe molecular vibrations within the junction, providing an in [...] Read more.

We present a comprehensive vibrational spectroscopic analysis of vertical molecular junction devices constructed using single-layer graphene electrodes separated by an aryl alkane monolayer. In this work, inelastic electron tunneling spectroscopy (IETS) is employed to probe molecular vibrations within the junction, providing an in situ fingerprint of the molecules. Graphene has emerged as a promising electrode material for molecular electronics due to its atomically thin, mechanically robust nature and ability to form stable contacts. However, prior to this study, the vibrational spectra of molecules in graphene-based molecular junctions had not been fully explored. Here, we demonstrate that vertically stacked graphene electrodes can be used to form stable and reproducible molecular junctions that yield well-resolved IETS signatures. The observed IETS spectra exhibit distinct peaks corresponding to the vibrational modes of the sandwiched aryl alkane molecules, and all major features are assigned through density functional theory calculations of molecular vibrational modes. Furthermore, by analyzing the broadening of IETS peaks with temperature and AC modulation amplitude, we extract intrinsic vibrational linewidths, confirming that the spectral features originate from the molecular junction itself rather than extrinsic noise or instrumental artifacts. These findings conclusively verify the presence of the molecular layer between graphene electrodes as the charge transport pathway and highlight the potential of graphene–molecule–graphene junctions for fundamental studies in molecular electronics. Full article

(This article belongs to the Special Issue Advances in Multifunctional Materials and Structures)

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19 pages, 9508 KiB

Open AccessEditor’s ChoiceArticle

Preparation, Microstructure, and Properties of Solar Energy-Absorbing and -Storing Integrated Forsterite-Based Ceramics

by Xiaohong Xu, Yuntian Li, Tiantian Cheng, Jianfeng Wu, Yaqiang Shen, Saixi Qiu and Jiaqi Yu

Crystals 2025, 15(5), 427; https://doi.org/10.3390/cryst15050427 - 30 Apr 2025

Viewed by 370

Abstract

Solar energy-absorbing and -storing integrated ceramics are a new type of material that absorbs sunlight and stores it as heat energy, with properties such as high absorptivity, high thermal storage density, and high temperature stability. In this study, forsterite ceramics were prepared from [...] Read more.

Solar energy-absorbing and -storing integrated ceramics are a new type of material that absorbs sunlight and stores it as heat energy, with properties such as high absorptivity, high thermal storage density, and high temperature stability. In this study, forsterite ceramics were prepared from fused magnesia, quartz, α-Al₂O₃, and Sm₂O₃, and concurrently, two additives of Fe₂O₃ and CuO were doped to improve the absorptivity, and the effects of the composite additives on the performance of forsterite ceramics were investigated. The results showed that the optimal Fe₂O₃/CuO content ratio was 8:2, at which time the apparent porosity, bulk density, and thermal storage density of the sample were 0.21%, 3.08 g/cm³, and 1516.71 kJ/kg (1000 °C), respectively. After 30 thermal shock cycles, the precipitation of samarium silicate in the samples resulted in a tighter grain bonding, increased the bending strength by 70.6%, and exhibited excellent thermal shock resistance. The solar absorptivity reached 93.80% in the 0.3–2.5 μm wavelength range. Fe₂O₃ doping replaced part of the positions of Al³⁺ in MgAl₂O₄ to form MgFe_0.6Al_1.4O₄ phase. This replacement caused lattice distortion, which triggered electronic transition and augmented the intrinsic absorption capacity, thereby enhancing the sample’s absorptivity. CuO’s low reflectivity across the spectrum further reduced sample reflectivity. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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14 pages, 5493 KiB

Open AccessEditor’s ChoiceArticle

Evolution of Microstructure, Tensile Mechanical and Corrosion Properties of a Novel Designed TRIP-Aided Economical 19Cr Duplex Stainless Steel After Aging Treatment

by Xi Shi, Shan Liu, Shuaiwei Chen, Qingxuan Ran, Bo Liang and Xiaoliang Yan

Crystals 2025, 15(5), 419; https://doi.org/10.3390/cryst15050419 - 29 Apr 2025

Viewed by 295

Abstract

In this experiment, a novel designed Mn-N-bearing, nearly Ni-free, TRIP-aided economical 19Cr (Fe-18.9Cr-10.1Mn-0.3Ni-0.26N-0.03C) duplex stainless steel (DSS) was prepared, and it exhibited a good combination of strength and toughness after suitable solution treatment, showing good application potential. The deformation mechanisms of ferrite and [...] Read more.

In this experiment, a novel designed Mn-N-bearing, nearly Ni-free, TRIP-aided economical 19Cr (Fe-18.9Cr-10.1Mn-0.3Ni-0.26N-0.03C) duplex stainless steel (DSS) was prepared, and it exhibited a good combination of strength and toughness after suitable solution treatment, showing good application potential. The deformation mechanisms of ferrite and austenite are different during tensile deformation at room temperature: the ferrite phase was deformed by a dislocation slip mechanism and formed a cell structure due to its higher stacking fault energy; the lower stacking fault energy of austenite resulted in a strain-induced martensite phase transformation mechanism. With an increase in aging time from 1 h to 7 h at 750 °C in air, the σ phase precipitates in the ferrite triple grain boundary junction, which leads to an increase in ultimate tensile strength, acts as an obstacle to the dislocation motion and decreases the ductility, deteriorating the pitting corrosion resistance in 3.5 wt.% NaCl solution at the same time. The σ phase precipitation behavior does not alter the deformation mechanism of the phases of the solution-treated TRIP-aided economical DSS. Full article

(This article belongs to the Special Issue Microstructure and Properties of Steels and Other Structural Alloys, Second Edition)

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20 pages, 2259 KiB

Open AccessEditor’s ChoiceArticle

Temperature-Controlled Defective Phononic Crystals with Shape Memory Alloys for Tunable Ultrasonic Sensors

by Soo-Ho Jo

Crystals 2025, 15(5), 412; https://doi.org/10.3390/cryst15050412 - 28 Apr 2025

Cited by 2 | Viewed by 464

Abstract

Phononic crystals (PnCs) have garnered significant interest owing to their ability to manipulate wave propagation, particularly through phononic band gaps and defect modes. However, conventional defective PnCs are limited by their fixed defect-band frequencies, which restricts their adaptability to dynamic environments. This study [...] Read more.

Phononic crystals (PnCs) have garnered significant interest owing to their ability to manipulate wave propagation, particularly through phononic band gaps and defect modes. However, conventional defective PnCs are limited by their fixed defect-band frequencies, which restricts their adaptability to dynamic environments. This study introduces a novel approach for temperature-controlled tunability of defective PnCs by integrating shape memory alloys (SMAs) into defect regions. The reversible phase transformations of SMAs, driven by temperature variations, induce significant changes in their mechanical properties, enabling real-time adjustment of defect-band frequencies. An analytical model is developed to predict the relationship between the temperature-modulated material properties and defect-band shifts, which is validated through numerical simulations. The results demonstrate that defect-band frequencies can be dynamically controlled within a specified range, thereby enhancing the operational bandwidth of the ultrasonic sensors. Additionally, sensing-performance analysis confirms that while defect-band frequencies shift with temperature, the output voltage of the sensors remains stable, ensuring reliable sensitivity across varying conditions. This study represents a significant advancement in tunable PnC technology, paving the way for next-generation ultrasonic sensors with enhanced adaptability and reliability in complex environments. Full article

(This article belongs to the Special Issue Research and Applications of Acoustic Metamaterials)

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15 pages, 2675 KiB

Open AccessEditor’s ChoiceArticle

Crystal Chemistry and Genetic Implications of Pink Tourmalines from Distinct Pegmatite Provinces

by Floriana Rizzo, Ferdinando Bosi, Gioacchino Tempesta, Federica Iommazzo and Giovanna Agrosì

Crystals 2025, 15(5), 415; https://doi.org/10.3390/cryst15050415 - 28 Apr 2025

Viewed by 391

Abstract

Borosilicate minerals of the tourmaline supergroup are valuable both for collectors and for geological research, as their chemical composition reflects the growth-medium conditions and their evolution. Tourmalines show a wide compositional variability, with pink tourmalines being particularly prized as gemstones. This study examines [...] Read more.

Borosilicate minerals of the tourmaline supergroup are valuable both for collectors and for geological research, as their chemical composition reflects the growth-medium conditions and their evolution. Tourmalines show a wide compositional variability, with pink tourmalines being particularly prized as gemstones. This study examines the crystal chemistry of pink tourmalines from Cruzeiro (Brazil), Nuristan (Afghanistan), and Malkhan (Russia) using Electron Microprobe Analysis, Micro Laser Induced Breakdown Spectroscopy (LIBS), and Single Crystal X-ray Diffraction. The results show that the pink tourmalines are Mn-rich elbaite, with the pink coloration linked to Mn at the Y site, indicating crystallization from Mn-rich pegmatitic fluids. LIBS spectra suggest a Li-rich pegmatite origin. The samples show differences: Cruzeiro exhibits strong chemical zoning, Nuristan has a uniform composition, and Malkhan shows slight zoning with high F content. A comparison with a pink tourmaline from Anjanabonoina (Madagascar) reveals that it is Ca-rich, belonging to the calcic group and crystallizing in an open system influenced by external Ca-rich fluids, contrasting with the closed system of the samples from Cruzeiro and Nuristan. The sample from Malkhan shows an anomalous chemical variation of Ca and requires further investigation. Full article

(This article belongs to the Section Mineralogical Crystallography and Biomineralization)

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11 pages, 1890 KiB

Open AccessEditor’s ChoiceArticle

First-Principles Study on the Migration and Release Properties of Xe on the Surface of Uranium Mononitride

by Tianhao Rui, Yulin Lan, Zhuangzhuang Ma, Linyuan Lu, Yunhao Wang, Yang Yu, Mingxuan Deng, Tianxing Lan, Zhekang Zhao, Junjie Wang, Congyi Li and Haibin Zhang

Crystals 2025, 15(5), 409; https://doi.org/10.3390/cryst15050409 - 27 Apr 2025

Viewed by 347

Abstract

The fission gas uranium mononitride (UN) causes swelling and affects the properties of fission fuel. Since surface behavior is closely related to the release of gases, it is crucial to study the properties of Xe on the UN surface. Density functional theory was [...] Read more.

The fission gas uranium mononitride (UN) causes swelling and affects the properties of fission fuel. Since surface behavior is closely related to the release of gases, it is crucial to study the properties of Xe on the UN surface. Density functional theory was used to study the properties of Xe gas on the UN(001) surface and subsurface layers. Different bulk and surface models of UN were established, and the formation energies of bulk and surface defects, as well as the incorporation energy of surface Xe, were calculated. Differential charge density maps were generated, and the analysis revealed that the migration of Xe atoms on the surface predominantly occurs through a vacancy mechanism. Furthermore, Xe atoms located in the subsurface and interstitial positions are less likely to escape from the surface due to the influence of surrounding atoms. Finally, the Climbing Image Nudged Elastic Band method was employed to calculate migration pathways and the associated migration energies. The modelling results indicated that surface Xe atoms’ migration exhibits a vacancy-assisted mechanism, while surface and subsurface U-vacancies on the UN surface may promote the diffusion of fission gas atoms. Full article

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19 pages, 6524 KiB

Open AccessEditor’s ChoiceArticle

Hydrogen-Bonded Ladder Motifs in Naphthalene Dicarboxamides: Influence of Linear vs. Angular Amide Orientation

by Abdulrahman Mohabbat, István Boldog, Takin Haj Hassani Sohi, Nils Reistel, Philipp Seiffert and Christoph Janiak

Crystals 2025, 15(5), 406; https://doi.org/10.3390/cryst15050406 - 26 Apr 2025

Viewed by 784

Abstract

The crystal structures of naphthalene dicarboxamides, namely 1,4-naphthalene dicarboxamide (1,4-NDA), 2,6-naphthalene dicarboxamide (2,6-NDA), and 2,7-naphthalene dicarboxamide (2,7-NDA), are presented for the first time, along with an analysis of their supramolecular organization. The compounds, obtained in single-crystalline form via solvothermal crystallization from methanol, are [...] Read more.

The crystal structures of naphthalene dicarboxamides, namely 1,4-naphthalene dicarboxamide (1,4-NDA), 2,6-naphthalene dicarboxamide (2,6-NDA), and 2,7-naphthalene dicarboxamide (2,7-NDA), are presented for the first time, along with an analysis of their supramolecular organization. The compounds, obtained in single-crystalline form via solvothermal crystallization from methanol, are stable in air to near 350 °C and have melting points above 300 °C. In their densely packed structures (ρ = 1.43–1.47 cm³g⁻¹) the combination of

C_{1}^{1}

(4) chains and

R_{2}^{2}

(8) rings generates one-dimensional hydrogen-bonded ladders, with an additional

R_{4}^{2}

(8) pattern. The amide groups and the naphthalene rings form dihedral angles between 22° and 40°. Neighboring H-bond ladders run parallel in 1,4-NDA and 2,6-NDA and are connected by means of the naphthalenedyil cores so that two-dimensional (2D) H-bonded sheets are obtained. Except for a weak intra-sheet π–π stacking in 1,4-NDA, there are no π–π stacking and C–H⋯π interactions. The

R_{2}^{2}

(8) rings act as four-connected nodes, leading to the formation of two-dimensional H-bonded planar sheets with sql topology for the nearly linear dicarboxamides 1,4-NDA and 2,6-NDA and cds topology for the angular 2,7-NDA. Hirshfeld surface analysis and NCI plots provide additional insight into the H-bonding interactions. Full article

(This article belongs to the Section Crystal Engineering)

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15 pages, 2187 KiB

Open AccessEditor’s ChoiceReview

Sustainable Strategies for Wine Colloidal Stability: Innovations in Potassium Bitartrate Crystallization Control

by Yuhan Zhang

Crystals 2025, 15(5), 401; https://doi.org/10.3390/cryst15050401 - 25 Apr 2025

Viewed by 657

Abstract

Potassium bitartrate (KHT) crystallization, as the dominant factor compromising wine colloidal stability, necessitates advanced control strategies beyond conventional thermodynamic approaches. The formation of tartrate crystals is influenced by various factors, including temperature, pH, and the concentration of tartrate salts. Traditional methods of tartrate [...] Read more.

Potassium bitartrate (KHT) crystallization, as the dominant factor compromising wine colloidal stability, necessitates advanced control strategies beyond conventional thermodynamic approaches. The formation of tartrate crystals is influenced by various factors, including temperature, pH, and the concentration of tartrate salts. Traditional methods of tartrate stabilization, such as cold stabilization and ion-exchange resins, while effective, are associated with high energy consumption and significant environmental impact. In recent years, with the growing emphasis on green and sustainable development, researchers have begun exploring more environmentally friendly innovative technologies. This review examines the factors affecting tartrate crystallization and their implications for wine quality, detailing traditional stabilization techniques as well as newer methods involving protective colloids and stabilizers. Special attention is given to recent advancements in green technologies, such as plasma surface modification, the use of zeolites as wine processing aids, and the synergistic application of algal polysaccharides. Finally, the paper outlines future directions for tartrate stabilization technology, underscoring the importance of green and sustainable practices in the wine industry. Full article

(This article belongs to the Section Liquid Crystals)

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14 pages, 6074 KiB

Open AccessEditor’s ChoiceArticle

Cu₂S Nanocrystals and Their Superlattices

by Samuel Fuentes, Ryan Hart, Juan Ramirez, Aditi Mulgaonkar, Rainie Luo, Brady Killham, Sashi Debnath, Yunfeng Wang, Xiankai Sun, Jiechao Jiang and Yaowu Hao

Crystals 2025, 15(5), 387; https://doi.org/10.3390/cryst15050387 - 23 Apr 2025

Viewed by 498

Abstract

We report the successful synthesis of monodispersed Cu₂S nanocrystals and the subsequent formation of highly ordered nanocrystal superlattices. The synthesis is performed under ambient air conditions using simple experimental setups, making the process both accessible and scalable. By systematically tuning the [...] Read more.

We report the successful synthesis of monodispersed Cu₂S nanocrystals and the subsequent formation of highly ordered nanocrystal superlattices. The synthesis is performed under ambient air conditions using simple experimental setups, making the process both accessible and scalable. By systematically tuning the reaction temperature and duration, we demonstrate precise control over the nanocrystal size, which is crucial in achieving uniformity and monodispersity. Furthermore, we uncover a previously unidentified nanocrystal growth mechanism that plays a key role in producing highly monodisperse Cu₂S nanocrystals. This insight into the growth process enhances our fundamental understanding of nanocrystal formation and could be extended to the synthesis of other semiconductor nanomaterials. The self-assembly of these nanocrystals into superlattices is carefully examined using electron diffraction techniques, revealing the presence of pseudo-crystalline structures. The ordered arrangement of nanocrystals within these superlattices suggests strong interparticle interactions and opens up new possibilities to tailor their collective optical, electronic, and mechanical properties for potential applications in optoelectronics, nanomedicine, and energy storage. Full article

(This article belongs to the Special Issue Celebrating the 10th Anniversary of International Crystallography)

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26 pages, 5096 KiB

Open AccessEditor’s ChoiceArticle

Chromone-Based Copper(II) Complexes as Potential Antitumour Agents: Synthesis, Chemical Characterisation and In Vitro Biological Evaluation

by Nikolina Filipović, Tomislav Balić, Martina Medvidović-Kosanović, Dominik Goman, Berislav Marković, Dalibor Tatar, Sunčica Roca and Katarina Mišković Špoljarić

Crystals 2025, 15(5), 389; https://doi.org/10.3390/cryst15050389 - 23 Apr 2025

Viewed by 561

Abstract

Three new complexes of copper(II) and chromone-2-carboxylic acid, a ligand from the group of hydroxypyrones, were synthesised according to the principles of green chemistry. The complexes were characterised by FT–IR and NMR spectroscopy, thermal and electrochemical analysis, and their structures are proposed. The [...] Read more.

Three new complexes of copper(II) and chromone-2-carboxylic acid, a ligand from the group of hydroxypyrones, were synthesised according to the principles of green chemistry. The complexes were characterised by FT–IR and NMR spectroscopy, thermal and electrochemical analysis, and their structures are proposed. The results show the formation of mononuclear (1) and dinuclear hydroxo-bridged dinuclear copper(II) complexes (2 and 3). The results of cyclic voltammetry show that the copper in all complexes is in the +2-oxidation state. The antiproliferative activity was determined by MTT assay on 2D cell models in vitro on seven cell lines. The activity spectrum of complexes 1–3 ranged from the highest to the lowest value in the tumour cell lines tested, in the following order: Hep G2 > NCI-H358 > HT-29 > KATO III > MDA-MB 231 > Caco-2. The most effective concentration was 10⁻⁵ mol dm⁻³, which suppressed the growth of Hep G2 cells as follows: 69.5% (1), 64.8% (2) and 64% (3). The calculated selectivity index clearly shows that Hep G2 is the most sensitive cell line to copper complexes (SI = 1.623 (1); 1.557 (2), 1.431 (3). Full article

(This article belongs to the Special Issue Green Approach in Synthesis of Bio-Inspired Materials (Second Edition))

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19 pages, 4638 KiB

Open AccessEditor’s ChoiceArticle

Structural and Optical Properties of Defected and Exotic Calcium Monochalcogenide Nanoparticles: Insights from DFT and TD-DFT Calculations

by Panagiotis G. Moustris, Alexandros G. Chronis, Fotios I. Michos, Nikos Aravantinos-Zafiris and Mihail M. Sigalas

Crystals 2025, 15(5), 392; https://doi.org/10.3390/cryst15050392 - 23 Apr 2025

Viewed by 615

Abstract

In this work, the structural and optical properties of calcium monochalcogenide nanoparticles were numerically examined by using Density Functional Theory and Time Dependent Density Functional Theory. The composition of the examined nanoparticles was obtained from an initial cubic-like building block of the form [...] Read more.

In this work, the structural and optical properties of calcium monochalcogenide nanoparticles were numerically examined by using Density Functional Theory and Time Dependent Density Functional Theory. The composition of the examined nanoparticles was obtained from an initial cubic-like building block of the form Ca₄Y₄, where Y could be one of the chalcogen elements sulfur, selenium, and tellurium, after its proper numerical examination to check their structural stability. The examined nanoparticles were then created from these initial cubic-like building blocks after their elongation along one, two, and three perpendicular directions. Τhe Absorption Spectrum, the Binding Energy, together with the highest occupied-lowest unoccupied molecular orbital (HOMO-LUMO) gap, were included in the calculations of the studied calcium monochalcogenides. The calculations provided numerical evidence regarding the existence of stable structures for a wide range of morphologies. In addition, the examination of the properties of such nanostructures after placing different kinds of defects was also included in the calculations, thus leading to new groups of nanoparticles with several potential uses in technological applications, such as hydrogen storage, CO₂ capture, and ultraviolet-responsive devices. Full article

(This article belongs to the Special Issue Celebrating the 10th Anniversary of International Crystallography)

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18 pages, 1358 KiB

Open AccessEditor’s ChoiceArticle

Learning Self-Supervised Representations of Powder-Diffraction Patterns

by Shubhayu Das, Markus Vorholt, Andreas Houben and Richard Dronskowski

Crystals 2025, 15(5), 393; https://doi.org/10.3390/cryst15050393 - 23 Apr 2025

Viewed by 855

Abstract

The potential of machine learning (ML) models for predicting crystallographic symmetry information from single-phase powder X-ray diffraction (XRD) patterns is investigated. Given the scarcity of large, labeled experimental datasets, we train our models using simulated XRD patterns generated from crystallographic databases. A key [...] Read more.

The potential of machine learning (ML) models for predicting crystallographic symmetry information from single-phase powder X-ray diffraction (XRD) patterns is investigated. Given the scarcity of large, labeled experimental datasets, we train our models using simulated XRD patterns generated from crystallographic databases. A key challenge in developing reliable diffraction-based structure-solution tools lies in the limited availability of training data and the presence of natural adversarial examples, which hinder model generalization. To address these issues, we explore multiple training pipelines and testing strategies, including evaluations on experimental XRD data. We introduce a contrastive representation learning approach that significantly outperforms previous supervised learning models in terms of robustness and generalizability, demonstrating improved invariance to experimental effects. These results highlight the potential of self-supervised learning in advancing ML-driven crystallographic analysis. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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18 pages, 7231 KiB

Open AccessEditor’s ChoiceArticle

Electron Beam Welding of Dissimilar Ti6Al4V and Al6082-T6 Alloys Using Magnetron-Sputtered Cu Interlayers

by Georgi Kotlarski, Darina Kaisheva, Maria Ormanova, Milka Atanasova, Angel Anchev, Vladimir Dunchev, Borislav Stoyanov and Stefan Valkov

Crystals 2025, 15(4), 373; https://doi.org/10.3390/cryst15040373 - 18 Apr 2025

Viewed by 451

Abstract

In the present work, the influence of a magnetron-sputtered copper interlayer on the process of electron beam welding of Ti6Al4V and Al6082-T6 plates was investigated. A sample without a filler was also prepared as a control. The microstructure, microhardness, and tensile properties of [...] Read more.

In the present work, the influence of a magnetron-sputtered copper interlayer on the process of electron beam welding of Ti6Al4V and Al6082-T6 plates was investigated. A sample without a filler was also prepared as a control. The microstructure, microhardness, and tensile properties of both samples were determined. Applying a copper interlayer resulted in the formation of an additional CuAl₂ intermetallic compound in the form of a eutectic structure along the boundary of the aluminum crystal grains. A noticeable shift in the preferred crystallographic orientation of the aluminum phase from the denser {111} family of crystallographic planes in the case of the sample prepared without a filler towards less-dense ones such as {110}, {100}, and {311} in the case of applying a copper filler was observed. This was most probably caused by the lower free surface energy of the crystals oriented towards the {111} family of crystal planes, which favored the chemical bonding between the aluminum solid solution and the CuAl₂ intermetallics. As a result of applying the copper interlayer, a noticeable increase in the microhardness of the weld seam was observed from 78 ± 2 HV0.05 to 136 ± 3 HV0.05. Applying a copper interlayer also led to an improved energy absorption capacity of the weld seam, as suggested by the increase in the UTS/YS ratio from 1.03 to 1.44. This could be explained by the smooth transition between the highly dissimilar Ti6Al4V and Al6082-T6 alloys. The UTS of the sample with the copper filler reached 208 MPa, which was about 60% of that of the base Al6082-T6 alloy. Full article

(This article belongs to the Special Issue Advanced Welding and Additive Manufacturing)

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18 pages, 7058 KiB

Open AccessEditor’s ChoiceArticle

Molecular Structure and GPR35 Receptor Docking of 1,3-Phenylene Bis-Oxalamide Derivatives

by Juan Saulo González-González, José Martín Santiago-Quintana, José Luis Madrigal-Angulo, Lina Barragán-Mendoza, Nancy E. Magaña-Vergara, Efrén V. García-Báez, Itzia Irene Padilla-Martínez and Francisco Javier Martínez-Martínez

Crystals 2025, 15(4), 371; https://doi.org/10.3390/cryst15040371 - 17 Apr 2025

Viewed by 454

Abstract

A series of three 1,3-phenylene bis-oxamides 3a–c, structurally related to the GPR35 receptor-agonist drug lodoxamide, has been synthesized by reacting the 1,3-phenylene bis-oxalamates 2a and 2b with amines. The obtained compounds were characterized by ¹H and ¹³C NMR, [...] Read more.

A series of three 1,3-phenylene bis-oxamides 3a–c, structurally related to the GPR35 receptor-agonist drug lodoxamide, has been synthesized by reacting the 1,3-phenylene bis-oxalamates 2a and 2b with amines. The obtained compounds were characterized by ¹H and ¹³C NMR, and IR spectroscopy, they showed characteristic signals for the aromatic, N―H, and C=O groups. Molecular structure was determined using single-crystal X-ray diffraction. The supramolecular architecture is driven by N―H···O=C, N―H···N, C—H···π, and O=C···O=C interactions depicting a supramolecular helix (3a) and tapes (3b–c). Intermolecular interactions were studied using Hirshfeld surface analysis, where N―H∙∙∙X (X = N, O) hydrogen bonding represents 30.2% to the surface of 3a and 17.8–18.8% to the surface of 3b–c. The most energetic interactions involve the amide N—H∙∙∙O hydrogen bonding, contributing in the −113.9 to −97.0 kJ mol⁻¹ range to the crystal energy, being more dispersive than electrostatic in nature. The molecular docking study was performed to evaluate the binding ability of 3a–c compounds to the GPR35 receptor, showing a favorable binding in a similar way to lodoxamide. Full article

(This article belongs to the Section Biomolecular Crystals)

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20 pages, 3934 KiB

Open AccessEditor’s ChoiceArticle

Microstructure and High-Temperature Compressive Properties of a Core-Shell Structure Dual-MAX-Phases-Reinforced TiAl Matrix Composite

by Shiqiu Liu and Huijun Guo

Crystals 2025, 15(4), 363; https://doi.org/10.3390/cryst15040363 - 16 Apr 2025

Viewed by 380

Abstract

As an advanced high-temperature structural material, TiAl alloy, is often used in the manufacturing of hot-end components of aviation and aerospace engines. However, it is difficult to increase the strength at high temperature, which limits its wider application. Adopting composite material technology is [...] Read more.

As an advanced high-temperature structural material, TiAl alloy, is often used in the manufacturing of hot-end components of aviation and aerospace engines. However, it is difficult to increase the strength at high temperature, which limits its wider application. Adopting composite material technology is one of the effective ways to improve the comprehensive mechanical properties of TiAl alloy. In this work, by adding 3 wt.% SiC micro-particles to Ti-47.5Al-7Nb-0.4W-0.1B (at.%) pre-alloyed powder, a core-shell structure dual-MAX-phase high-temperature strengthened TiAl matrix composite (also known as TiAl-SiC composite) was prepared by combining powder metallurgy and hot forging. The microstructure and high-temperature compressive properties of the prepared TiAl-SiC composites were studied and compared with TiAl alloy prepared by the same process, and the microstructural characteristics of the TiAl-SiC composite and its microstructure evolution during processing were revealed. The results show that the matrix of as-sintered TiAl-SiC composites was mainly composed of γ phase and a small amount of Ti₂AlC particles, while the reinforcement phase was a dual-MAX-phase core-shell structure, which was mainly composed of core Ti₂AlC phase, shell Ti₃SiC₂ phase, and small Ti₂AlC particles distributed in the outer layer. After hot forging, the microstructure of TiAl-SiC composite became more compact, finer, and more uniform; the phase composition was almost not changed, but the content of Ti₂AlC, Ti₃SiC₂, and TiB₂ phases increased significantly; the content of C in each constituent phase decreased obviously, and a granular Si-rich phase was generated in the core of the reinforcement phase. The yield strength of the as-forged TiAl-SiC composite was significantly higher than that of the as-forged TiAl alloy at temperature higher than 859 °C. This is because the core-shell structure dual MAX phases can effectively reduce the softening rate of TiAl alloy in the range of 800–900 °C, thus playing a strengthening role and increasing the service temperature of TiAl alloy. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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21 pages, 13359 KiB

Open AccessEditor’s ChoiceArticle

A Novel Zinc-Based MOF Featuring 2,4,6-Tris-(4-carboxyphenoxy)-1,3,5-triazine: Structure, Adsorption, and Photocatalytic Activity

by Magdalena Angelova, Hristina Lazarova, Vanya Kurteva, Rositsa Nikolova, Rusi Rusew and Boris Shivachev

Crystals 2025, 15(4), 348; https://doi.org/10.3390/cryst15040348 - 8 Apr 2025

Viewed by 578

Abstract

A metal–organic framework, MOF-S1, was synthesized via a solvothermal reaction between 2,4,6-tris-(4-carboxyphenoxy)-1,3,5-triazine (TCPT) and zinc nitrate hexahydrate. Single-crystal and powder X-ray diffraction analyses confirmed the formation of hexagonal rod-shaped crystals with a trigonal (P-31c) structure featuring a two-fold interpenetrated 3D framework. [...] Read more.

A metal–organic framework, MOF-S1, was synthesized via a solvothermal reaction between 2,4,6-tris-(4-carboxyphenoxy)-1,3,5-triazine (TCPT) and zinc nitrate hexahydrate. Single-crystal and powder X-ray diffraction analyses confirmed the formation of hexagonal rod-shaped crystals with a trigonal (P-31c) structure featuring a two-fold interpenetrated 3D framework. A comprehensive characterization—including NMR spectroscopy, thermogravimetric analysis, and surface area measurements (using Langmuir, t-plot, Horváth–Kawazoe, and Dubinin–Radushkevich models)—revealed an ultramicroporous material with a Langmuir surface area of 711 m²/g and a median pore width of ~6.5 Å. Adsorption studies using Congo Red, Methylene Blue, Methyl Orange, and Rhodamine B demonstrated the rapid uptake and effective removal from aqueous solutions, with kinetic modeling indicating a dominant chemisorption mechanism. Photocatalytic tests under UV irradiation yielded degradation efficiencies of ~93% for Methyl Orange and ~74% for Rhodamine B. These findings suggest that MOF-S1 is a promising candidate for wastewater treatment applications and UV-related processes, offering a strong adsorption capacity and thermal stability. Full article

(This article belongs to the Special Issue Feature Papers on “Hybrid and Composite Crystalline Materials” 2025)

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34 pages, 10030 KiB

Open AccessEditor’s ChoiceArticle

Seven New Irbesartan Salts: Significantly Improved Dissolution, Excellent Hygrothermal Stability, and Characteristic Supramolecular Synthons

by Junxiao Wang, Chuanhua Wu, Menglong Zhang, Lingli Hou, Wei Chen, Dingding Jing and Ying Bao

Crystals 2025, 15(4), 342; https://doi.org/10.3390/cryst15040342 - 4 Apr 2025

Viewed by 408

Abstract

Irbesartan (IRB) is a commonly used BCS Class II antihypertensive drug requiring dissolving capacity enhancement to address oral bioavailability limitations. In this work, seven new IRB salts were successfully synthesized, including one carboxylate (IRB-MAL) and six sulfonate salts (IRB-TOSA, IRB-BSA, IRB-4-CBSA, IRB-2, 5-CBSA, [...] Read more.

Irbesartan (IRB) is a commonly used BCS Class II antihypertensive drug requiring dissolving capacity enhancement to address oral bioavailability limitations. In this work, seven new IRB salts were successfully synthesized, including one carboxylate (IRB-MAL) and six sulfonate salts (IRB-TOSA, IRB-BSA, IRB-4-CBSA, IRB-2, 5-CBSA, IRB-MSA, and IRB-CPSA). Their vitro dissolution, intrinsic dissolution rates (IDRs), thermal/hygroscopic stability (via thermal analysis, dynamic vapor sorption, and accelerated stability tests), and phase transition process (monitored by in situ Raman spectroscopy) were evaluated. The results revealed that IRB-TOSA, IRB-MAL, IRB-BSA, IRB-4-CBSA, and IRB-MSA salts exhibited IDRs of 0.3194–0.7383 mg/(cm²·min), all significantly higher than IRB, with dissolution concentrations increased by 14.9–113.6%. IRB-TOSA and IRB-4-CBSA salts demonstrated excellent hydrothermal stability. Single crystal structure analysis confirmed proton transfer from coformers’ sulfonic/carboxylic acids (deprotonation site, H-out) to IRB’s diazaheterocycles (protonation site, H-in) in IRB salts. Six sulfonate salts exhibited N_H-in–H···O_H-out and N_non-H-in–H···O_H-out hydrogen bonds, with the former absent in IRB-MAL. Furthermore, supramolecular synthon studies revealed distinct hydrogen-bonding patterns (e.g., bifurcated bonds in 2,5-CBSA and CPSA salts) that correlate with moisture resistance. Quantitative analysis of IRB salts suggested hydrogen bond strengths may influence their melting points (decomposition temperatures). This study demonstrates that IRB salts hold promise for advanced pharmaceutical applications. Full article

(This article belongs to the Section Crystal Engineering)

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12 pages, 7852 KiB

Open AccessEditor’s ChoiceArticle

Remineralization Effects of Zinc-Containing Glass Ionomer Cement Restoratives on Demineralized Enamel Under pH Cycling Conditions

by Khin Myanmar, Go Inoue, Xuefei Chen and Yasushi Shimada

Crystals 2025, 15(4), 329; https://doi.org/10.3390/cryst15040329 - 29 Mar 2025

Viewed by 495

Abstract

(1) Background: White spot lesions (WSLs) on enamel result from demineralization and are an early sign of dental caries. Glass ionomer cement (GIC) has been widely used for its remineralization potential, and zinc-containing GIC (zGIC) has been introduced to enhance this effect. However, [...] Read more.

(1) Background: White spot lesions (WSLs) on enamel result from demineralization and are an early sign of dental caries. Glass ionomer cement (GIC) has been widely used for its remineralization potential, and zinc-containing GIC (zGIC) has been introduced to enhance this effect. However, its efficacy compared to conventional GIC (cGIC) remains unclear. This study aimed to evaluate and compare the remineralization effects of cGIC and zGIC on WSLs. (2) Methods: Thirty-six bovine enamel specimens were prepared, demineralized for four days, and divided into three groups: control, cGIC, and zGIC. Half of each specimen’s treated window was covered with varnish, and a two-week pH cycling protocol was conducted. Mineral density (MD) changes were assessed using microcomputed tomography (Micro-CT) at five time points: pre-demineralization, after demineralization, immediately after treatment, and 1- and 2-weeks post-treatment. Scanning electron microscopy (SEM) was also performed. (3) Results: MD values in the zGIC and cGIC groups were significantly higher than in the control group throughout every post-treatment assessment (p < 0.05). zGIC demonstrated significantly higher MD than cGIC (p < 0.05), and SEM images revealed inferior mineral deposition. (4) Conclusions: These findings suggest that zGIC is more effective in remineralizing WSLs than cGIC over two weeks. Full article

(This article belongs to the Special Issue Bioinspired Mineralization of Dental Tissues)

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13 pages, 4136 KiB

Open AccessEditor’s ChoiceArticle

Biphasic WO₃ Nanostructures via Controlled Crystallization: Achieving High-Performance Electrochromism Through Amorphous/Crystalline Heterointerface Design

by Xuefeng Chu, Kunjie Lin, Haiyang Zhao, Zonghui Yao, Yaodan Chi, Chao Wang and Xiaotian Yang

Crystals 2025, 15(4), 324; https://doi.org/10.3390/cryst15040324 - 28 Mar 2025

Viewed by 428

Abstract

WO₃ electrochromic films have emerged as potential candidates for smart windows due to their cost-effectiveness, fast switching speed, and strong chemical stability. However, the inherent contradiction between the high coloring efficiency of amorphous WO₃ and the cycling durability of crystalline WO [...] Read more.

WO₃ electrochromic films have emerged as potential candidates for smart windows due to their cost-effectiveness, fast switching speed, and strong chemical stability. However, the inherent contradiction between the high coloring efficiency of amorphous WO₃ and the cycling durability of crystalline WO₃ remains a critical challenge in practical applications. This study proposes an innovative heterostructure engineering strategy, achieving precise control of the amorphous/crystalline bilayer WO₃ heterointerface (148 nm a-WO₃/115 nm c-WO₃) for the first time through phase boundary regulation, using well-controlled magnetron sputtering and post-deposition thermal annealing processes. Multimodal characterization using XRD, XPS, and SEM indicates that the heterointerface optimizes performance through a dynamic charge transfer mechanism and structural synergistic effects: the optimized bilayer structure achieves 76.57% optical modulation (at 630 nm) under −1.0 V and maintains a ΔT retention rate of 45.02% after 600 cycles, significantly outperforming single amorphous (8.34%) and crystalline films (14.34%). XPS analysis reveals a dynamic equilibrium mechanism involving W⁵⁺/Li⁺ at the interface, and the Li⁺ diffusion coefficient (D₀ = 4.29 × 10⁻¹⁰ cm²/s) confirms that the amorphous layer dominates rapid ion transport, while the crystalline matrix enhances structural stability through its ordered crystalline structure. This study offers a new paradigm for balancing the efficiency and longevity of electrochromic devices, with the compatibility of magnetic sputtering promoting the industrialization process of large-area smart windows. Full article

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13 pages, 2095 KiB

Open AccessEditor’s ChoiceArticle

Two-Dimensional Silver Bismuth Oxide/Bismuth Molybdate Z-Scheme Heterojunctions with Rich Oxygen Vacancies for Improved Pollutant Degradation and Bacterial Inactivation

by Yanhong Wang, Huijie Zhu, Pengli He, Mingyu Li, Yinhuan Cao, Yanqiang Du, Yun Wen, Yixiang Zhao, Xiaowen Liu and Yonglong Song

Crystals 2025, 15(4), 318; https://doi.org/10.3390/cryst15040318 - 27 Mar 2025

Viewed by 284

Abstract

The effective removal of organic pollutants and bacteria are of great significance considering the hazards to the environment and human health. The two-dimensional AgBiO₃/Bi₂MoO₆ heterojunction with rich oxygen vacancies was successfully fabricated via a hydrothermal method and systematically [...] Read more.

The effective removal of organic pollutants and bacteria are of great significance considering the hazards to the environment and human health. The two-dimensional AgBiO₃/Bi₂MoO₆ heterojunction with rich oxygen vacancies was successfully fabricated via a hydrothermal method and systematically characterized by various analytical techniques. The photocatalytic experimental results revealed that the addition of AgBiO₃ improved the photocatalytic performance of Bi₂MoO₆, and the AgBiO₃/Bi₂MoO₆-10 heterojunction possessed the best degradation effect toward RhB (72%) within 100 min, with 1.38 and 1.44 times higher activity than pure Bi₂MoO₆ and AgBiO₃, respectively. The bacteria were completely inactivated within 90 min by AgBiO₃/Bi₂MoO₆-10 heterojunction. The reason for the enhancement of photocatalytic activity was the synergistic effect between AgBiO₃ and Bi₂MoO₆. The constructed Z-scheme heterojunction with oxygen vacancies improved the separation efficiency of photo-induced electrons and holes and broadened the range of visible-light absorption. The trapping experiments and ESR indicated that superoxide radical and holes were the main reactive species. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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8 pages, 1936 KiB

Open AccessEditor’s ChoiceArticle

Thermally Induced Ion Magnetic Moment in H₄O Superionic State

by Xiao Liang, Junhao Peng, Fugen Wu, Renhai Wang, Yujue Yang, Xingyun Li and Huafeng Dong

Crystals 2025, 15(4), 304; https://doi.org/10.3390/cryst15040304 - 26 Mar 2025

Viewed by 354

Abstract

The hydrogen ions in superionic ice can move freely, playing the role of electrons in metals. Its electromagnetic behavior is the key to explaining the anomalous magnetic fields of Uranus and Neptune. Based on an ab initio evolutionary algorithm, we searched for the [...] Read more.

The hydrogen ions in superionic ice can move freely, playing the role of electrons in metals. Its electromagnetic behavior is the key to explaining the anomalous magnetic fields of Uranus and Neptune. Based on an ab initio evolutionary algorithm, we searched for the stable H₄O crystal structure under pressures of 500–5000 GPa and discovered a new layered-chain Pmn2₁-H₄O structure with H₃ ion clusters. Interestingly, H₃ ion clusters rotate above 900 K (with an instantaneous speed of 3000 m/s at 900 K), generating an instantaneous magnetic moment (~10⁻²⁶ A·m² ≈ 0.001

μ_{B}

). Moreover, H ions diffuse in a direction perpendicular to the H-O atomic layer at 960–1000 K. This is because the hydrogen–oxygen covalent bonds within the hydrogen–oxygen plane hinder the diffusion behavior of H₃ ion clusters within the plane, resulting in the diffusion of H₃ ion clusters between the hydrogen–oxygen planes and the formation of a one-dimensional conductive superionic state. One-dimensional diffusion of ions may generate magnetic fields. We refer to these two types of magnetic moments as “thermally induced ion magnetic moments”. When the temperature exceeds 1000 K, H ions diffuse in three directions. When the temperature exceeds 6900 K, oxygen atoms diffuse and the system becomes fluid. These findings provide important references for people to re-recognize the physical and chemical properties of hydrogen and oxygen under high pressure, as well as the sources of abnormal magnetic fields in Uranus and Neptune. Full article

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14 pages, 12903 KiB

Open AccessEditor’s ChoiceArticle

Biochemical and Structural Characterization of Glyoxylate Reductase/Hydroxypyruvate Reductase from Bacillus subtilis

by Thang Quyet Nguyen, Thai Huu Duong, Jin Kuk Yang and Wonchull Kang

Crystals 2025, 15(4), 298; https://doi.org/10.3390/cryst15040298 - 25 Mar 2025

Viewed by 468

Abstract

D-2-hydroxyacid dehydrogenases (2HADHs) catalyze the reversible reaction of 2-ketocarboxylic acid to the corresponding (R)-2-hydroxycarboxylic acids using NAD(P)H cofactor. As the preference of the cofactor and substrate varies among homologs, biochemical characterization is required to understand this enzyme. Here, we analyzed the biochemical properties [...] Read more.

D-2-hydroxyacid dehydrogenases (2HADHs) catalyze the reversible reaction of 2-ketocarboxylic acid to the corresponding (R)-2-hydroxycarboxylic acids using NAD(P)H cofactor. As the preference of the cofactor and substrate varies among homologs, biochemical characterization is required to understand this enzyme. Here, we analyzed the biochemical properties of Bacillus subtilis glyoxylate reductase/hydroxypyruvate reductase (BsGRHPR), which catalyzes the reduction of both glyoxylate (EC 1.1.1.26) and hydroxypyruvate (EC 1.1.1.81). Enzyme kinetics showed a preference for hydroxypyruvate over glyoxylate, with a seven-fold higher specificity constant. In addition, BsGRHPR displayed a strict preference for NADPH over NADH as a cofactor. The crystal structures of BsGRHPR in complex with formate were determined in the presence and absence of the cofactor at near-atomic resolution. Structural comparisons revealed conformational changes upon cofactor binding and key residues, such as Asp80, R157, R179, R239, Asp263, and Arg296. In addition, substrate-binding analysis highlighted conserved residues, including Val77, Gly78, His287, and S290. Our structures suggest that Glu137, His287, Ser290, and Arg296 serve as gatekeepers at the entrance of the tunnel. This comprehensive characterization of BsGRHPR elucidates its substrate specificity, cofactor preference, and catalytic mechanism, contributing to a broader understanding of GRHPR family enzymes, with potential implications for metabolic engineering applications. Full article

(This article belongs to the Special Issue Crystallography of Enzymes)

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13 pages, 3390 KiB

Open AccessEditor’s ChoiceArticle

Mössbauer and Optical Investigations on Sr Doped M-Type BaFe₁₂O₁₉ Hexaferrites Produced via Autocombustion

by Benilde F. O. Costa, Adel Benali, Bruno J. C. Vieira, João C. Waerenborgh, João Pina, Yousra Marouani and Essebti Dhahri

Crystals 2025, 15(4), 291; https://doi.org/10.3390/cryst15040291 - 24 Mar 2025

Viewed by 465

Abstract

Ba_1−xSr_xFe₁₂O₁₉ (x = 0.0, 0.5 and 1.0) hard-magnetic nanohexaferrites prepared by autocombustion were primarily investigated using Mössbauer spectroscopy and optical studies. Morphological examination by electron scanning microscopy revealed that the particles agglomerated into grains with a [...] Read more.

Ba_1−xSr_xFe₁₂O₁₉ (x = 0.0, 0.5 and 1.0) hard-magnetic nanohexaferrites prepared by autocombustion were primarily investigated using Mössbauer spectroscopy and optical studies. Morphological examination by electron scanning microscopy revealed that the particles agglomerated into grains with a hexagonal shape. The grain size increases with the amount of Sr content, from ca. 490 nm (x = 0.0) to ca. 700 nm (x = 1.0). Room-temperature Mössbauer spectroscopy showed that the mean hyperfine field increased with the substitution of Ba²⁺ by Sr²⁺, consistent with magnetization results. The preferential sites occupied by Fe ions in the hexaferrite structure were determined. Optical studies revealed that all compounds absorb up to ca. 1000 nm, and that the bandgap energy decreases with increasing Sr content. Full article

(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition))

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20 pages, 4199 KiB

Open AccessEditor’s ChoiceArticle

The Stirring Effect on the Crystal Morphology of p-Acetamidobenzoic Acid Solution Crystallization

by Rui Dong, Fan Wang, Dingding Jing, Yong Liu and Ying Bao

Crystals 2025, 15(3), 284; https://doi.org/10.3390/cryst15030284 - 20 Mar 2025

Viewed by 670

Abstract

This work investigates the stirring effect on p-Acetamidobenzoic Acid (p -AABA) crystal morphology through single crystal cultivation, crystal face growth rate, and nucleation supersaturation measurements, molecular simulation (MS), and computational fluid dynamics (CFD). Results show that stirring rate influences nucleation supersaturation, [...] Read more.

This work investigates the stirring effect on p-Acetamidobenzoic Acid (p -AABA) crystal morphology through single crystal cultivation, crystal face growth rate, and nucleation supersaturation measurements, molecular simulation (MS), and computational fluid dynamics (CFD). Results show that stirring rate influences nucleation supersaturation, boundary layer thickness on the {101} and {010} faces, and shear stress applied on these two faces. This leads to changes in nucleation rate, nucleus size, and relative growth rates between the {101} and {010} faces, thus affecting crystal morphology. Under low-rate stirring (150 rpm), crystals exhibit a small size, a low aspect ratio, and a clear aggregation phenomenon. Appropriately increasing stirring rate can prevent aggregation and improve particle size and crystal aspect ratio. High-rate stirring leads to a higher shear stress at the corner points of the {101} face, causing crystal fragmentation, which leads to a significant decrease in crystal size and a slow decrease in aspect ratio. Moreover, the growth rates of the {101} and {010} faces exhibit an exponential dependence on supersaturation. The {101} face grows faster than the {010} face, and this growth rate difference widens with the increasing supersaturation. This study provides a theoretical basis and practical guidance for optimizing crystal morphology in stirred solution crystallization. Full article

(This article belongs to the Section Crystal Engineering)

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26 pages, 6566 KiB

Open AccessEditor’s ChoiceReview

The B30.2/SPRY-Domain: A Versatile Binding Scaffold in Supramolecular Assemblies of Eukaryotes

by Peer R. E. Mittl and Hans-Dietmar Beer

Crystals 2025, 15(3), 281; https://doi.org/10.3390/cryst15030281 - 19 Mar 2025

Viewed by 764

Abstract

B30.2 domains, sometimes referred to as PRY/SPRY domains, were originally identified by sequence profiling methods at the gene level. The B30.2 domain comprises a concanavalin A-like fold consisting of two twisted seven-stranded anti-parallel β-sheets. B30.2 domains are present in about 150 human and [...] Read more.

B30.2 domains, sometimes referred to as PRY/SPRY domains, were originally identified by sequence profiling methods at the gene level. The B30.2 domain comprises a concanavalin A-like fold consisting of two twisted seven-stranded anti-parallel β-sheets. B30.2 domains are present in about 150 human and 700 eukaryotic proteins, usually fused to other domains. The B30.2 domain represents a scaffold, which, through six variable loops, binds different unrelated peptides or endogenous low-molecular-weight compounds. At the cellular level, B30.2 proteins engage in supramolecular assemblies with important signaling functions. In humans, B30.2 domains are often found in E3-ligases, such as tripartite motif (Trim) proteins, SPRY domain-containing SOCS box proteins, Ran binding protein 9 and −10, Ret-finger protein-like, and Ring-finger proteins. The B30.2 protein recognizes the target and recruits the E2-conjugase by means of the fused domains, often involving specific adaptor proteins. Further well-studied B30.2 proteins are the methyltransferase adaptor protein Ash2L, some butyrophilins, and Ryanodine Receptors. Although the affinity of an isolated B30.2 domain to its ligand might be weak, it can increase strongly due to avidity effects upon recognition of oligomeric targets or in the context of macromolecular machines. Full article

(This article belongs to the Special Issue Protein Crystallography: The State of the Art)

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18 pages, 15306 KiB

Open AccessEditor’s ChoiceReview

Emission Wavelength Control via Molecular Structure Design of Dinuclear Pt(II) Complexes: Optimizing Optical Properties for Red- and Near-Infrared Emissions

by Hea Jung Park

Crystals 2025, 15(3), 273; https://doi.org/10.3390/cryst15030273 - 15 Mar 2025

Viewed by 752

Abstract

Phosphorescent Pt(II) complexes have garnered significant attention as key components in luminescence-based systems due to their highly efficient emission properties. A notable characteristic of these complexes is their ability to form excimers through strong molecular stacking in concentrated solutions or solid film states. [...] Read more.

Phosphorescent Pt(II) complexes have garnered significant attention as key components in luminescence-based systems due to their highly efficient emission properties. A notable characteristic of these complexes is their ability to form excimers through strong molecular stacking in concentrated solutions or solid film states. This aggregation-driven emission, primarily arising from metal–metal to ligand charge transfer (MMLCT), is influenced by overlapping d-orbitals oriented perpendicular to the square planar structure of the Pt(II) complexes. Although this property hinders the development of pure blue-emitting Pt(II) complexes, it facilitates the design of materials that emit red- and near-infrared (NIR) light. By employing advanced molecular design techniques, dinuclear Pt(II) complexes have been optimized to significantly enhance red and NIR emissions through the modulation of Pt-Pt interactions and adjustments in ligand electron densities. This review elucidates how the control of Pt-Pt distances and strategic ligand modifications can directly influence the emission spectra toward red and NIR regions. A comparative analysis of recent studies underscores the novelty and effectiveness of double-decker-type dinuclear Pt(II) complexes in achieving efficient emission characteristics in the long-wavelength range. These insights may guide the design of molecular structures for next-generation organometallic phosphorescent materials. Full article

(This article belongs to the Special Issue Feature Papers on “Hybrid and Composite Crystalline Materials” 2025)

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17 pages, 4834 KiB

Open AccessEditor’s ChoiceReview

Advancements in the Research on the Preparation and Growth Mechanisms of Various Polymorphs of Calcium Carbonate: A Comprehensive Review

by Cheng-Gong Lu, Chu-Jie Jiao, Xiu-Cheng Zhang, Jian-Sheng Zheng and Xue-Fei Chen

Crystals 2025, 15(3), 265; https://doi.org/10.3390/cryst15030265 - 13 Mar 2025

Viewed by 1005

Abstract

Calcium Carbonate (CC) exhibits broad application prospects and significant market demand due to its diverse polymorphs, each with distinct potential for application in various fields. Consequently, the preparation of CC with specific polymorphs has emerged as a research hotspot. This paper commences with [...] Read more.

Calcium Carbonate (CC) exhibits broad application prospects and significant market demand due to its diverse polymorphs, each with distinct potential for application in various fields. Consequently, the preparation of CC with specific polymorphs has emerged as a research hotspot. This paper commences with an overview of the structure of CC, followed by an analysis of the advantages and disadvantages, as well as the mechanisms, of common preparation methods such as physical methods, chemical carbonation processes, and double displacement reactions. Special emphasis is placed on elucidating the influence of polymorph control agents (including inorganic ions, sugars, alcohols, and acids), process conditions (temperature, stirring rate, pH, and solution mixing rate), and reactor configurations (rotating packed beds and high-gravity reactors) on the polymorph regulation of CC. This paper points out how these factors alter the crystal formation process. Furthermore, it introduces the nucleation and growth control of CC crystallization, analyzing the mechanisms underlying these two processes. Research indicates that the carbonation process is currently a relatively mature preparation technique, with multiple factors synergistically influencing the polymorph and particle size of CC. Future efforts should focus on further improving production processes, exploring novel polymorph control agents, and delving deeper into the intrinsic mechanisms of polymorph control to achieve efficient preparation of diverse CC types. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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11 pages, 4438 KiB

Open AccessEditor’s ChoiceArticle

Effects of Zr Alloying on Microstructure Evolution and Mechanical Properties of CoCrNi Medium Entropy Alloy

by Ao Li, Zurong Gong, Dong Li, Xiaohong Wang, Yunting Su, Tengfei Ma, Bin Liu and Baochen Zhang

Crystals 2025, 15(3), 258; https://doi.org/10.3390/cryst15030258 - 10 Mar 2025

Viewed by 594

Abstract

Alloying provides an effective approach to designing metallic materials with unique microstructures and enhanced performance. In this work, we developed a series of (CoCrNi)_100−xZr_x (where x = 1, 2, 3, 4, and 5) medium entropy alloys (MEAs) by vacuum arc-melting [...] Read more.

Alloying provides an effective approach to designing metallic materials with unique microstructures and enhanced performance. In this work, we developed a series of (CoCrNi)_100−xZr_x (where x = 1, 2, 3, 4, and 5) medium entropy alloys (MEAs) by vacuum arc-melting method. The effects of Zr addition on the microstructures and mechanical properties of (CoCrNi)_100−xZr_x MEAs were systematically investigated. Due to the negative mixing enthalpy of Zr with Co, Cr, and Ni, lamellar C15 Laves-phase precipitates formed within the ductile FCC matrix. As the Zr content increases, the alloys exhibit higher strength but become more brittle at room temperature. Among the (CoCrNi)_100−xZr_x MEAs series, the CoCrNiZr₃ MEA shows an excellent balance between strength and ductility, achieving a compressive yield strength of 610 MPa and a hardness of 249 HV, respectively, while maintaining a good ductility beyond 45%. Microstructural analysis using scanning electron microscope and transmission electron microscope suggests that this outstanding strength-ductility balance of CoCrNiZr₃ MEA arises from the synergistic effect of precipitation strengthening and solid solution strengthening. These findings not only provide deeper insight into the interaction between different strengthening mechanisms but also offer valuable guidance for designing high-performance multi-component alloys through strategic alloying. Full article

(This article belongs to the Special Issue Microstructure and Deformation of Advanced Alloys)

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16 pages, 986 KiB

Open AccessEditor’s ChoiceArticle

Formation of Ice I_h Clusters in Solid-Phase Glacial Water with Low Concentrations of Ca²⁺ and Mg²⁺ Ions

by Ignat Ignatov, Yordan G. Marinov, Paunka Vassileva, Teodora P. Popova, Georgi Gluhchev, Mario T. Iliev, Fabio Huether, Zhechko Dimitrov and Irina Gotova

Crystals 2025, 15(3), 254; https://doi.org/10.3390/cryst15030254 - 9 Mar 2025

Cited by 3 | Viewed by 855

Abstract

This study explores the structural and chemical interactions between glacial water, ice I_h, and hydration clusters of divalent cations (Ca²⁺ and Mg²⁺). Ice I_h, with its hexagonal lattice and tetrahedral bonding network, is incompatible with [...] Read more.

This study explores the structural and chemical interactions between glacial water, ice I_h, and hydration clusters of divalent cations (Ca²⁺ and Mg²⁺). Ice I_h, with its hexagonal lattice and tetrahedral bonding network, is incompatible with the hydration shells of Ca²⁺ and Mg²⁺, which adopt octahedral geometries in aqueous solutions. During freezing, these hydration clusters become disordered, causing distortions in the ice structure. Slow freezing reduces these distortions, while rapid freezing traps ions in amorphous regions, preventing proper alignment of hydration clusters. Through advanced techniques such as chemical and isotopic analysis, computational modeling, and electrical impedance spectroscopy, this study examines ion exclusion mechanisms and water-clustering behaviors. The results show that both ions are largely excluded from the solid phase during freezing, with Mg²⁺ exhibiting stronger exclusion due to its smaller ionic radius and greater hydration energy. This study also highlights the role of sediments in modulating ion patterns in glacial ice. This work deepens our understanding of ion–ice interactions, offering insights for cryochemistry, hydrology, and environmental science. The integration of experimental and computational methods provides new perspectives on divalent cations’ role in modifying ice’s crystalline structure and explains isotopic variability in glacial waters. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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11 pages, 3987 KiB

Open AccessEditor’s ChoiceArticle

Induced Chirality in CuO Nanostructures Using Amino Acid-Mediated Chemical Bath Deposition

by Lama Jabreen and Yitzhak Mastai

Crystals 2025, 15(3), 236; https://doi.org/10.3390/cryst15030236 - 28 Feb 2025

Viewed by 568

Abstract

This study explored the controlled formation of chiral copper(II) oxide (CuO) crystals using chiral amino acids as chirality-inducing agents. Utilizing chemical bath deposition (CBD) as the fabrication method, we achieved simple, reproducible synthesis suitable for industrial-scale applications. Our characterization of the induced chirality [...] Read more.

This study explored the controlled formation of chiral copper(II) oxide (CuO) crystals using chiral amino acids as chirality-inducing agents. Utilizing chemical bath deposition (CBD) as the fabrication method, we achieved simple, reproducible synthesis suitable for industrial-scale applications. Our characterization of the induced chirality through high-performance liquid chromatography (HPLC), circular dichroism (CD), and isothermal titration calorimetry (ITC) revealed distinctive chiral features. These findings not only advance our understanding of chirality control in inorganic nanostructures but also establish CBD as a viable technique for the large-scale production of chiral materials. Full article

(This article belongs to the Topic Advances in Molecular Symmetry and Chirality Research)

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20 pages, 6430 KiB

Open AccessEditor’s ChoiceArticle

Multi-Scale Numerical Simulation of Short Tungsten Fiber Reinforced Tungsten–Copper Composites: Influence Mechanisms of Fiber Parameters

by Longchao Zhuo, Yixing Xie, Hang Xu, Bin Luo, Nan Liu, Bingqing Chen and Hao Wang

Crystals 2025, 15(3), 209; https://doi.org/10.3390/cryst15030209 - 22 Feb 2025

Viewed by 567

Abstract

Tungsten fiber reinforced tungsten–copper (W_f/W-Cu) composites have broad application prospects in fields such as electronic packaging due to their excellent comprehensive properties. However, the correlation between fiber parameters (content, aspect ratio, orientation) and the mechanical behavior of the materials is not [...] Read more.

Tungsten fiber reinforced tungsten–copper (W_f/W-Cu) composites have broad application prospects in fields such as electronic packaging due to their excellent comprehensive properties. However, the correlation between fiber parameters (content, aspect ratio, orientation) and the mechanical behavior of the materials is not yet clear. In this study, a combination of numerical simulation and experimental research was employed to construct a three-dimensional microstructural mechanic model and systematically investigate the influence of fiber parameters on the tensile properties and mechanisms of W_f/W-Cu composites. The results show that: (1) The critical fiber aspect ratio is 7.6. When below this value, fiber pullout dominates, and when above this value, fiber tensile fracture is the main mechanism. (2) As the fiber content increases from 1% to 6%, the tensile strength of the composite increases by 9.6%, the yield strength increases by 10.2%, while the elongation after fracture decreases by 18.6%. (3) As the fiber orientation angle increases from 0° to 90°, the material strength first increases and then decreases, while the toughness first decreases and then increases. (4) Short fibers achieve interface toughening through fiber pullout, crack deflection, and fiber bridging, while long fibers improve the strength and toughness of the composite through load transfer and fiber bridging effects. (5) The damage evolution mechanism reveals the regulation effect of fiber parameters on the multi-scale mechanical behavior of the material. The research results can guide the composition and structure optimization design of W_f/W-Cu composites, provide new ideas for the research of high-performance fiber composites, and have important significance for their engineering applications in extreme environments. Full article

(This article belongs to the Special Issue Advances in Metal Matrix Composites: Structure, Properties and Applications)

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10 pages, 2660 KiB

Open AccessEditor’s ChoiceArticle

Crystal Growth and Energy Transfer Study in Ce³⁺ and Pr³⁺ Co-Doped Lu₂Si₂O₇

by Yuka Abe, Takahiko Horiai, Yuui Yokota, Masao Yoshino, Rikito Murakami, Takashi Hanada, Akihiro Yamaji, Hiroki Sato, Yuji Ohashi, Shunsuke Kurosawa, Kei Kamada and Akira Yoshikawa

Crystals 2025, 15(3), 202; https://doi.org/10.3390/cryst15030202 - 20 Feb 2025

Viewed by 523

Abstract

Ce-doped Lu₂Si₂O₇ has a high density, high luminescence efficiency even at high temperatures, and a high effective atomic number, making it a promising candidate for use as a radiation detector in medical devices and resource exploration equipment. In [...] Read more.

Ce-doped Lu₂Si₂O₇ has a high density, high luminescence efficiency even at high temperatures, and a high effective atomic number, making it a promising candidate for use as a radiation detector in medical devices and resource exploration equipment. In this study, we grow and characterize Pr³⁺ and Ce³⁺-doped Lu₂Si₂O₇ single crystals by systematically varying the Ce³⁺ to Pr³⁺ ratio to further improve scintillation properties. The optical characterization results show a bidirectional energy transfer: from the Pr³⁺ 5d levels to the Ce³⁺ 5d levels and from the Ce³⁺ 5d levels to the Pr³⁺ 4f levels. Consistently with this result, the PL decay time of emission from the Pr³⁺ 5d–4f transition tends to become faster as the Ce³⁺/Pr³⁺ ratio increases, due to the energy transfer from the Pr³⁺ 5d levels to the Ce³⁺ 5d levels. Additionally, (Ce_0.0022 Pr_0.0016 Lu_0.9962)₂Si₂O₇ exhibits a high light yield comparable to Ce-doped Lu₂Si₂O₇ and a slightly faster decay time than Ce-doped Lu₂Si₂O₇. Full article

(This article belongs to the Special Issue Growth and Properties of Novel Scintillator Crystals)

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29 pages, 8842 KiB

Open AccessEditor’s ChoiceReview

Development and Research Status of Wear-Resistant Coatings on Copper and Its Alloys: Review

by Fei Meng, Yifan Zhou, Hongliang Zhang, Zhilan Wang, Dehao Liu, Shuhe Cao, Xue Cui, Zhisheng Nong, Tiannan Man and Teng Liu

Crystals 2025, 15(3), 204; https://doi.org/10.3390/cryst15030204 - 20 Feb 2025

Cited by 1 | Viewed by 1532

Abstract

Wear-resistant coatings applied to the surface of copper and copper alloys through diverse advanced technologies can substantially enhance their wear resistance and broaden their application spectrum. This paper provides a comprehensive review of the development and current research status of wear-resistant coatings fabricated [...] Read more.

Wear-resistant coatings applied to the surface of copper and copper alloys through diverse advanced technologies can substantially enhance their wear resistance and broaden their application spectrum. This paper provides a comprehensive review of the development and current research status of wear-resistant coatings fabricated on copper and its alloys. It presents the research findings on the preparation of wear-resistant coatings using both one-step methods (such as laser cladding, electroplating, thermal spraying, cold spraying, electro-spark deposition, etc.) and two-step methods (chemical plating and heat treatment, electrodeposition and laser cladding, laser cladding and in situ synthesis, etc.). This paper provides an in-depth examination of the characteristics, operating principles, and effects of various coating techniques on enhancing the wear resistance of copper and copper alloys. The advantages and disadvantages of different coating preparation methods are compared and analyzed; meanwhile, a prospective outlook on the future development trends is also offered. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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57 pages, 13524 KiB

Open AccessEditor’s ChoiceReview

Recent Developments in Transmission Electron Microscopy for Crystallographic Characterization of Strained Semiconductor Heterostructures

by Tao Gong, Longqing Chen, Xiaoyi Wang, Yang Qiu, Huiyun Liu, Zixing Yang and Thomas Walther

Crystals 2025, 15(2), 192; https://doi.org/10.3390/cryst15020192 - 17 Feb 2025

Viewed by 2026

Abstract

With recent electronic devices relying on sub-nanometer features, the understanding of device performance requires a direct probe of the atomic arrangement. As an ideal tool for crystallographic analysis at the nanoscale, aberration-corrected transmission electron microscopy (ACTEM) has the ability to provide atomically resolved [...] Read more.

With recent electronic devices relying on sub-nanometer features, the understanding of device performance requires a direct probe of the atomic arrangement. As an ideal tool for crystallographic analysis at the nanoscale, aberration-corrected transmission electron microscopy (ACTEM) has the ability to provide atomically resolved images and core-loss spectra. Herein, the techniques for crystallographic structure analysis based on ACTEM are reviewed and discussed, particularly ACTEM techniques for measuring strain, dislocations, phase transition, and lattice in-plane misorientation. In situ observations of crystal evolution during the application of external forces or electrical fields are also introduced, so a correlation between crystal quality and device performance can be obtained. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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20 pages, 4387 KiB

Open AccessEditor’s ChoiceArticle

Polymorphism of the Transition Metal Oxidotellurates NiTeO₄ and CuTe₂O₅

by Matthias Weil and Enrique J. Baran

Crystals 2025, 15(2), 183; https://doi.org/10.3390/cryst15020183 - 14 Feb 2025

Viewed by 725

Abstract

As part of crystal growth experiments on transition metal oxidotellurates using chemical vapor transport reactions or hydrothermal conditions, single crystals of Ni^IITe^VIO₄ and Cu^IITe^IV₂O₅ were obtained for the first time in the [...] Read more.

As part of crystal growth experiments on transition metal oxidotellurates using chemical vapor transport reactions or hydrothermal conditions, single crystals of Ni^IITe^VIO₄ and Cu^IITe^IV₂O₅ were obtained for the first time in the form of new modifications, as revealed by crystal structure determinations from X-ray data. In the course of these investigations, the crystal structure model of the only phase of Ni^IITe^VIO₄ reported so far (from now on named α-) was corrected. Both α-(space group P2₁/c, Z = 2) and the new β-polymorph of Ni^IITe^VIO₄ (space group I4₁/a, Z = 8) can be considered derivatives (hettotypes) of the rutile structure (aristotype), as shown by detailed symmetry relationships. For CuTe₂O₅ also, only one crystalline phase has been described so far (from now on named α-) that corresponds to the mineral rajite (space group P2₁/c, Z = 2). Its anion comprises two different trigonal-pyramidal TeO₃ groups linked through corner-sharing into a ditellurite unit. The anion part of the new β-CuTe₂O₅ modification (space group P2₁/c, Z = 2), likewise, comprises two Te^IV atoms but is more complex. Here, one Te^IV atom exhibits a coordination number of 4 and is part of a

{}_{\propto}^{1}[

TeO_2/2O_2/1] chain, and the other has a coordination number of 5 and is part of a

{}_{\propto}^{1}[

TeO_2/2O_3/1]₂ dimer. The two types of anions are linked into a tri-periodic framework where both Te^IV atoms are stereochemically active. The α- and β-CuTe₂O₅ modifications show no closer structural relationship, which is also reflected in their clearly different Raman spectra. Data mining for knowledge discovery in a structure database reveals that polymorphism is a rather common phenomenon for the family of inorganic oxidotellurates. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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15 pages, 3338 KiB

Open AccessEditor’s ChoiceArticle

One-Pot Strategies for Lithium Recovery from Beta-Spodumene and LTA-Type Zeolite Synthesis

by Leonardo Leandro dos Santos, Rubens Maribondo do Nascimento and Sibele Berenice Castellã Pergher

Crystals 2025, 15(2), 161; https://doi.org/10.3390/cryst15020161 - 8 Feb 2025

Viewed by 766

Abstract

This study presents a groundbreaking method for extracting lithium from beta-spodumene while simultaneously achieving the sustainable synthesis of LTA-type zeolite, designated as LPM-15, without relying on organic solvents or calcination. Lithium extraction was efficiently performed using sodium salts, accompanied by the recycling of [...] Read more.

This study presents a groundbreaking method for extracting lithium from beta-spodumene while simultaneously achieving the sustainable synthesis of LTA-type zeolite, designated as LPM-15, without relying on organic solvents or calcination. Lithium extraction was efficiently performed using sodium salts, accompanied by the recycling of the mother liquor, with lithium content in the supernatant precisely quantified via atomic absorption spectroscopy (AAS). The optimized synthesis route enables the concurrent production of Li₂CO₃ and LPM-15, distinguished by a powdered appearance without a well-defined geometric framework and a unique cubic morphology with spherical facets, respectively. To gain deeper insights into the process, density functional theory (DFT) simulations were conducted to analyze how different cation exchanges (Na⁺ replacing Al³⁺, NH₄⁺ replacing Al³⁺, and Ca²⁺ replacing Al³⁺) influence the structural stability and diffusion dynamics within the zeolitic pores of LPM-15. Additionally, cation-exchange capacity (CEC) measurements further assessed ion mobility within the LPM-15 framework. This integrative approach not only sheds light on the fundamental mechanisms underpinning LTA-type zeolite synthesis but also demonstrates their versatile applications, with particular emphasis on water purification technologies. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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21 pages, 17365 KiB

Open AccessEditor’s ChoiceArticle

Regulating the Mechanical and Corrosion Properties of Mg-2Zn-0.1Y Alloy by Trace SiC with Different Morphologies

by Furong Guo, Kaibo Nie, Kunkun Deng and Yanan Li

Crystals 2025, 15(2), 166; https://doi.org/10.3390/cryst15020166 - 8 Feb 2025

Viewed by 550

Abstract

Traditional magnesium structural materials are used widely due to their light weight; however, their corrosion resistance is poor. In order to address this problem and improve the strength simultaneously, SiCp-, SiCnp-, and SiCnw-reinforced Mg-2Zn-0.1Y (wt. %, MZY alloy) matrix composites (SiC/MZY composites) with [...] Read more.

Traditional magnesium structural materials are used widely due to their light weight; however, their corrosion resistance is poor. In order to address this problem and improve the strength simultaneously, SiCp-, SiCnp-, and SiCnw-reinforced Mg-2Zn-0.1Y (wt. %, MZY alloy) matrix composites (SiC/MZY composites) with the same contents (0.3 wt. %) were prepared and extruded at low temperature in this paper. The effects of SiC morphology on the microstructure, mechanical properties and corrosion resistance of MZY alloy were studied. The results show that the grain size can be refined by adding SiC reinforcement. Compared with the unreinforced MZY alloy, the strengths of the SiC/MZY composites were all improved, with a yield strength of more than 440 MPa and an ultimate tensile strength of more than 450 MPa. However, only the corrosion rate of the composites reinforced by submicron SiCp was improved significantly. The hydrogen evolution corrosion rate (P_H) was reduced by 81% relative to the MZY alloy. This can be attributed to the decreased galvanic corrosion pairs, as well as the decreased potential difference between the second phase and the matrix in the SiCp/MZY composite. Additionally, a compact product film on the surface of the SiCp/MZY composite can also protect the matrix. The materials prepared in this study showed excellent strength and high corrosion resistance at relatively low cost, providing valuable insights and design ideas for the development and application of those materials in marine and offshore engineering applications. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Alloys and Composites)

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15 pages, 4738 KiB

Open AccessEditor’s ChoiceArticle

Estimation of Hardness of Single-Phase Metallic Alloys

by Ottó K. Temesi, Nguyen Q. Chinh, Levente Vitos and Lajos K. Varga

Crystals 2025, 15(2), 156; https://doi.org/10.3390/cryst15020156 - 2 Feb 2025

Cited by 1 | Viewed by 882

Abstract

First, we discuss a common feature of single-phase pure metals and amorphous and high-entropy alloys: the maximum value of hardness corresponding to a valence electron count (VEC) value of around 6.5–7. This correlation is explained by the coincidence that by subtracting the number [...] Read more.

First, we discuss a common feature of single-phase pure metals and amorphous and high-entropy alloys: the maximum value of hardness corresponding to a valence electron count (VEC) value of around 6.5–7. This correlation is explained by the coincidence that by subtracting the number of sp valence electrons (Nsp = 2) from the VEC we obtain the maximal number of unpaired d electrons, N_d = 4.5–5 in the 3d, 4d, and 5d rows of transition elements. These unpaired d electrons form orbital overlap bonding, which is stronger than the isotropic metallic bonds of a delocalized electron cloud. The more unpaired d electrons there are, the higher the bonding strength. Second, we will discuss the hardness formulas derived from cohesion energy and shear modulus. We will demonstrate that both types of formulas originate in the electrostatic energy density of metallic bonds, expressing a 1/R⁴ dependence. Finally, we show that only two parameters are sufficient to estimate hardness: the atomic radius and the cohesion-based valence. In the case of alloys, our formula gives a lower bound on the hardness only. It is not suitable for calculation of the hardness increase caused by solid solution, grain size, precipitation, and phase mixture. Full article

(This article belongs to the Special Issue Microstructure and Deformation of Advanced Alloys)

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17 pages, 8260 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Selected Crystal Structures of Rod-like Molecules with Acid and Ester Terminal Groups

by Peter Zugenmaier

Crystals 2025, 15(2), 102; https://doi.org/10.3390/cryst15020102 - 21 Jan 2025

Viewed by 723

Abstract

The crystal structures of rod-like molecules with nitro-biphenyl or nitro-phenyl end groups and attached n-alkyl units with terminal acid or ester groups are determined by single crystal analysis and their arrangements are compared. The molecules are linked by head-to-tail arrangements and form strings. [...] Read more.

The crystal structures of rod-like molecules with nitro-biphenyl or nitro-phenyl end groups and attached n-alkyl units with terminal acid or ester groups are determined by single crystal analysis and their arrangements are compared. The molecules are linked by head-to-tail arrangements and form strings. They point in a single or two different directions and are placed side by side to create the crystal structure. Some of the space groups of the structures can only be determined by a statistical routine because strongly disordered structures prevent the use of extinction methods, since many extinction violations occur for monoclinic and orthorhombic unit cells. An agreement between experimental and calculated X-ray reflection intensities serves as proof of the correctness of the method as well as a test of the existence of an inversion center. The single crystals are grown in solution with ethanol, isopropanol, DMAc, and toluene as solvents. Cocrystals are formed in DMAc solutions by the dissolved acid compounds. The two-molecule asymmetric unit of the acid compound is reduced to a one-molecule asymmetric unit with one DMAc included which forms a hydrogen bond with the acid group of the biphenyl molecule. These changes alter the hydrogen bonding scheme along a string. Some structural similarities as the head-to-tail arrangement in the strings are maintained between the terminal acid and ester compounds despite disordered ester groups in the compounds and the ester molecules themselves at ambient temperature. Full article

(This article belongs to the Section Crystal Engineering)

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16 pages, 16085 KiB

Open AccessEditor’s ChoiceArticle

Impact of Diffraction Data Volume on Data Quality in Serial Crystallography

by Ki Hyun Nam

Crystals 2025, 15(2), 104; https://doi.org/10.3390/cryst15020104 - 21 Jan 2025

Cited by 2 | Viewed by 1208

Abstract

Serial crystallography (SX) enables macromolecular structure determination at biologically relevant temperatures while minimizing radiation damage. This technique relies on processing numerous diffraction images from multiple crystals to construct a complete dataset for three-dimensional structure determination. Although increasing the volume of SX diffraction data [...] Read more.

Serial crystallography (SX) enables macromolecular structure determination at biologically relevant temperatures while minimizing radiation damage. This technique relies on processing numerous diffraction images from multiple crystals to construct a complete dataset for three-dimensional structure determination. Although increasing the volume of SX diffraction data improves data quality, excessive data collection reduces beamtime efficiency. Therefore, understanding the relationship between data volume and data quality is crucial for the efficient use of SX beamtime. In this study, serial synchrotron crystallography datasets from lysozyme and glucose isomerase were analyzed to assess the impact of varying diffraction data volumes on processing statistics and structural determination outcomes. Data processing statistics and structure refinement metrics improved as the volume of integrated diffraction data increased; however, the rate of improvement in data quality was not proportional to the number of integrated diffraction patterns. Furthermore, the rate of improvement in data processing statistics decreased beyond a certain threshold volume. These findings expand our understanding of SX data processing and provide insights into optimizing the efficiency of data processing. Full article

(This article belongs to the Section Biomolecular Crystals)

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12 pages, 2358 KiB

Open AccessEditor’s ChoiceArticle

Exploring Brannerite-Type Mg_1−xM_xV₂O₆ (M = Mn, Cu, Co, or Ni) Oxides: Crystal Structure and Optical Properties

by Hua-Chien Hsu, Narayanan Lakshminarasimhan, Jun Li, Arthur P. Ramirez and Mas A. Subramanian

Crystals 2025, 15(1), 86; https://doi.org/10.3390/cryst15010086 - 16 Jan 2025

Viewed by 1487

Abstract

Environmentally benign, highly stable oxides exhibiting desirable optical properties and high near-IR reflectance are being researched for their potential application as pigments. Mg_1−xM_xV₂O₆ (M = Mn, Cu, Co, or Ni) oxides with brannerite-type structures [...] Read more.

Environmentally benign, highly stable oxides exhibiting desirable optical properties and high near-IR reflectance are being researched for their potential application as pigments. Mg_1−xM_xV₂O₆ (M = Mn, Cu, Co, or Ni) oxides with brannerite-type structures were synthesized by the conventional solid-state reaction method to study their optical properties. These series exhibit structural transitions from brannerite (C2/m) to distorted brannerite (P

\bar{1}

) and NiV₂O₆-type (P

\bar{1}

) structures. The average color of Mg_1−xM_xV₂O₆ compounds varies from reddish-yellow to brown to dark brown. The L*a*b* color coordinates reveal that Mg_1−xCu_xV₂O₆ and Mg_1−xNi_xV₂O₆ show more red hues in color with x = 0.4 and x = 0.5, respectively. The UV–Vis diffuse reflectance spectra indicate a possible origin for these results include the ligand-to-metal charge transfer (O²⁻ 2p-V⁵⁺ 3d), metal-to-metal charge transfer (from Mn²⁺ 3d/Cu²⁺ 3d/Co²⁺ 3d/Ni²⁺ 3d to V⁵⁺ 3d), band gap transitions, and d–d transitions. Magnetic property measurements revealed antiferromagnetic behavior for the compounds Mg_1−xM_xV₂O₆ (M = Mn, Cu, Co, and Ni), and an oxidation state of +2 for the M ions was deduced from their Curie–Weiss behavior. The system Mg_1−xMn_xV₂O₆ has a NIR reflectance in the range between 40% and 70%, indicating its potential to be utilized in the pigment industry. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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13 pages, 1857 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Gradient Cooling Behavior on the Microstructure and Mechanical Properties of Al-2at.% Nd Alloy in a Vacuum Environment

by Xiangjie Wang, Xinyu Zhang, Wenjie Wu and Shuchen Sun

Crystals 2025, 15(1), 81; https://doi.org/10.3390/cryst15010081 - 15 Jan 2025

Cited by 1 | Viewed by 764

Abstract

Al-2at.% Nd alloy with a gradient cooling rate was prepared using a wedge-shaped mold in a vacuum environment. The relationship between gradient cooling behavior and the microstructure and properties of the Al-2at.% Nd alloy was investigated. The stability of the Al₁₁Nd [...] Read more.

Al-2at.% Nd alloy with a gradient cooling rate was prepared using a wedge-shaped mold in a vacuum environment. The relationship between gradient cooling behavior and the microstructure and properties of the Al-2at.% Nd alloy was investigated. The stability of the Al₁₁Nd₃ phase and the mechanical properties were confirmed through first-principles calculations. The results indicated that as the cooling rate decreased, the transformation of grain morphology in Al-2at.% Nd occurred as follows: a mixture of columnar grains and equiaxed grains→equiaxed grains. The grain size of the alloy increased. Discontinuous skeletal eutectic phases, α-Al and Al₁₁Nd₃, formed within the alloy, resulting in a reduction in the number of phase boundaries and grain boundaries. The hardness of the alloy decreased by 25.53%, and this pattern of change closely aligned with the calculated results. Full article

(This article belongs to the Special Issue Development of Light Alloys and Their Applications)

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22 pages, 11041 KiB

Open AccessEditor’s ChoiceArticle

Effect of Dynamic Corrosion and Degradation on Fatigue Life of an AA2024-T3 Aircraft Profile: Experimental, Statistical, and Numerical Analyses

by Gilberto Daniel Conejo Magaña, Víctor García García, Daniel Cahue Díaz, Nicolás Herrera-Sandoval and Orlando Hernández Cristóbal

Crystals 2025, 15(1), 66; https://doi.org/10.3390/cryst15010066 - 11 Jan 2025

Viewed by 889

Abstract

The effect of parameters such as angle of attack, flow velocity, and electrolyte concentration (saline solution) on the extent of material degradation, as well as the morphology and depth of corrosion pits in an airfoil made of 2024-T3 aluminum alloy, was studied in [...] Read more.

The effect of parameters such as angle of attack, flow velocity, and electrolyte concentration (saline solution) on the extent of material degradation, as well as the morphology and depth of corrosion pits in an airfoil made of 2024-T3 aluminum alloy, was studied in detail. An orthogonal L9 design of experiments (Taguchi method) was applied to promote high pitting corrosion through the quality characteristic “the higher the better”. Potentiodynamic curves of the three experiments with low, medium, and high saline concentration were obtained through the CorrTest CS350 equipment. The above allowed the determination of the electrochemical corrosion parameters under static test conditions. The corroded airfoils were analyzed using light optical microscopy (LOM). In addition, the roughness measurements correlated with the extent of the degraded surface. A complete pit shape and depth characterization was obtained by applying mechanical ground, surface wear level monitoring (every 0.01 mm), and LOM observations. Pitting defects (depth and morphology) and mechanical strength reduction were considered by a finite element (FE) model to simulate the airfoil fatigue behavior. Numerical results helped to determine the contribution of pitting and the extent of degradation on sudden airfoil failure. Full article

(This article belongs to the Special Issue Corrosion Phenomena in Metals)

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14 pages, 9251 KiB

Open AccessEditor’s ChoiceArticle

Synergistic Integration of Mesocarbon Microbeads, Graphitic Nanofibers, and Mesoporous Carbon for Advanced Supercapacitor Electrodes

by Palanisamy Rajkumar, Vediyappan Thirumal, Kisoo Yoo and Jinho Kim

Crystals 2025, 15(1), 64; https://doi.org/10.3390/cryst15010064 - 10 Jan 2025

Viewed by 654

Abstract

In this study, a novel multiscale carbon architecture was developed by integrating mesocarbon microbeads (MCMBs), graphitic nanofibers (GNFs), and mesoporous carbon, aimed at enhancing the performance of symmetric supercapacitors. The unique combination of spherical MCMB particles, conductive GNF nanofibers, and mesoporous carbon sheets [...] Read more.

In this study, a novel multiscale carbon architecture was developed by integrating mesocarbon microbeads (MCMBs), graphitic nanofibers (GNFs), and mesoporous carbon, aimed at enhancing the performance of symmetric supercapacitors. The unique combination of spherical MCMB particles, conductive GNF nanofibers, and mesoporous carbon sheets resulted in a highly effective electrode material, offering improved conductivity, increased active sites for charge storage, and enhanced structural stability. The fabricated MCMB/GNF/MC architecture demonstrated a remarkable specific capacitance of 393 F g⁻¹ at 1 A g⁻¹ in a three-electrode system, significantly surpassing the performance of individual MCMBs and MCMB/GNF electrodes. Furthermore, the architecture was incorporated into a symmetric supercapacitor (SSC) device, where it achieved a capacitance of 86 F g⁻¹ at 1 A g⁻¹. The device exhibited excellent cycling stability, retaining 92% of its initial capacitance after 10,000 charge–discharge cycles, with an outstanding coulombic efficiency of 99%. At optimal operating conditions, the SSC device delivered an energy density of 11 Wh kg⁻¹ at a power density of 500 W kg⁻¹, making it a promising candidate for high-performance energy-storage applications. This multiscale carbon architecture represents a significant advancement in the design of electrode materials for symmetric supercapacitors, offering a balance of high energy and power density, long-term stability, and excellent scalability for practical applications. This work not only contributes to the development of high-performance electrode materials but also paves the way for scalable, long-lasting supercapacitors for future energy-storage technologies. Full article

(This article belongs to the Special Issue Feature Papers on "Hybrid and Composite Crystalline Materials" 2023–2024)

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38 pages, 23114 KiB

Open AccessEditor’s ChoiceReview

Mathematical Modeling of Properties and Structures of Crystals: From Quantum Approach to Machine Learning

by Grzegorz Matyszczak, Christopher Jasiak, Gabriela Rusinkiewicz, Kinga Domian, Michał Brzozowski and Krzysztof Krawczyk

Crystals 2025, 15(1), 61; https://doi.org/10.3390/cryst15010061 - 9 Jan 2025

Viewed by 2121

Abstract

The crystalline state of matter serves as a reference point in the context of studies of properties of a variety of chemical compounds. This is due to the fact that prepared crystalline solids of practically useful materials (inorganic or organic) may be utilized [...] Read more.

The crystalline state of matter serves as a reference point in the context of studies of properties of a variety of chemical compounds. This is due to the fact that prepared crystalline solids of practically useful materials (inorganic or organic) may be utilized for the thorough characterization of important properties such as (among others) energy bandgap, light absorption, thermal and electric conductivity, and magnetic properties. For that reason it is important to develop mathematical descriptions (models) of properties and structures of crystals. They may be used for the interpretation of experimental data and, as well, for predictions of properties of novel, unknown compounds (i.e., the design of novel compounds for practical applications such as photovoltaics, catalysis, electronic devices, etc.). The aim of this article is to review the most important mathematical models of crystal structures and properties that vary, among others, from quantum models (e.g., density functional theory, DFT), through models of discrete mathematics (e.g., cellular automata, CA), to machine learning (e.g., artificial neural networks, ANNs). Full article

(This article belongs to the Special Issue Crystallization Process and Simulation Calculation, Third Edition)

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21 pages, 8328 KiB

Open AccessEditor’s ChoiceArticle

Impact of Buffer Layer on Electrical Properties of Bow-Tie Microwave Diodes on the Base of MBE-Grown Modulation-Doped Semiconductor Structure

by Algirdas Sužiedėlis, Steponas Ašmontas, Jonas Gradauskas, Aurimas Čerškus, Aldis Šilėnas and Andžej Lučun

Crystals 2025, 15(1), 50; https://doi.org/10.3390/cryst15010050 - 3 Jan 2025

Cited by 2 | Viewed by 732

Abstract

Bow-tie diodes on the base of modulation-doped semiconductor structures are often used to detect radiation in GHz to THz frequency range. The operation of the bow-tie microwave diodes is based on carrier heating phenomena in an epitaxial semiconductor structure with broken geometrical symmetry. [...] Read more.

Bow-tie diodes on the base of modulation-doped semiconductor structures are often used to detect radiation in GHz to THz frequency range. The operation of the bow-tie microwave diodes is based on carrier heating phenomena in an epitaxial semiconductor structure with broken geometrical symmetry. However, the electrical properties of bow-tie diodes are highly dependent on the purity of the grown epitaxial layer—specifically, the minimal number of defects—and the quality of the ohmic contacts. The quality of MBE-grown semiconductor structure depends on the presence of a buffer layer between a semiconductor substrate and an epitaxial layer. In this paper, we present an investigation of the electrical and optical properties of planar bow-tie microwave diodes fabricated using modulation-doped semiconductor structures grown via the MBE technique, incorporating either a GaAs buffer layer or a GaAs–AlGaAs super-lattice buffer between the semi-insulating substrate and the active epitaxial layer. These properties include voltage sensitivity, electrical resistance, I–V characteristic asymmetry, nonlinearity coefficient, and photoluminescence. The investigation revealed that the buffer layer, as well as the illumination with visible light, strongly influences the properties of the bow-tie diodes. Full article

(This article belongs to the Special Issue Growth, Structural Identification, and Characterization of Semiconductor Alloys and Low-Dimensional Heterostructures)

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12 pages, 7472 KiB

Open AccessEditor’s ChoiceArticle

The Effect of the Film Thickness, Cooling Rate, and Solvent Evaporation on the Formation of L-Menthol Ring-Banded Spherulites

by Tamás Kovács, Tamás Kovács, Jr., Márton Detrich, Ferenc Gazdag, Masaki Itatani and István Lagzi

Crystals 2025, 15(1), 17; https://doi.org/10.3390/cryst15010017 - 27 Dec 2024

Viewed by 1071

Abstract

Periodic pattern formation is a prominent phenomenon in chemical, physical, and geochemical systems. This phenomenon can arise from various processes, such as the reaction and mass transport of chemical species, solidification, or solvent evaporation. We investigated the formation of ring-banded spherulites of l [...] Read more.

Periodic pattern formation is a prominent phenomenon in chemical, physical, and geochemical systems. This phenomenon can arise from various processes, such as the reaction and mass transport of chemical species, solidification, or solvent evaporation. We investigated the formation of ring-banded spherulites of l-menthol using a thin liquid film in a Petri dish. We found that the film thickness and cooling rate strongly influence the generation of crystallization patterns. We performed two-dimensional numerical simulations using the Cahn–Hilliard model to support the experimentally observed trend on the dependence of the layer thickness on the periodicity of the generated macroscopic patterns. In a specific scenario, we observed the formation of rings consisting of needle-like crystals on the cover of the Petri dish. This phenomenon was due to the evaporation of the menthol and its subsequent crystallization. In addition to these findings, we created crystallization patterns by solvent evaporation (using tert-butyl alcohol, methyl alcohol, and acetone). Full article

(This article belongs to the Special Issue Crystallisation Advances)

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21 pages, 31902 KiB

Open AccessEditor’s ChoiceArticle

Analysis of Human Kidney Stones Using Advanced Characterization Techniques

by Jelena Brdarić Kosanović, Kristijan Živković, Vatroslav Šerić, Berislav Marković, Imre Szenti, Ákos Kukovecz, Nives Matijaković Mlinarić and Anamarija Stanković

Crystals 2025, 15(1), 6; https://doi.org/10.3390/cryst15010006 - 25 Dec 2024

Viewed by 1343

Abstract

A comprehensive analysis of kidney stones is essential for the future treatment of patients. Almost all of the methods available for kidney stone analysis were used in this study. The chemical analysis included powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), and [...] Read more.

A comprehensive analysis of kidney stones is essential for the future treatment of patients. Almost all of the methods available for kidney stone analysis were used in this study. The chemical analysis included powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA-DSC). Following the chemical analysis, a detailed morphological analysis was carried out using stereoscopic microscopy, scanning electron microscopy (SEM-EDX), and micro-computed tomography (micro-CT). These investigations showed that the sixteen kidney stones analyzed in detail had a heterogeneous mineralogical structure, consisting of at least two different minerals. Kidney stones consist mainly of calcium oxalate (whewellite or weddellite) but also contain significant amounts of phosphate (mainly apatite and struvite). A thorough analysis of kidney stones can determine the cause of their formation and investigate possible treatments. Full article

(This article belongs to the Section Biomolecular Crystals)

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17 pages, 3033 KiB

Open AccessEditor’s ChoiceArticle

Advanced Copper Oxide Chemical and Green Synthesis: Characterization and Antibacterial Evaluation

by Ecaterina Magdalena Modan, Adriana-Gabriela Schiopu, Sorin Georgian Moga, Denis Aurelian Negrea, Daniela Istrate, Ion Ciuca and Mihai Oproescu

Crystals 2025, 15(1), 7; https://doi.org/10.3390/cryst15010007 - 25 Dec 2024

Cited by 3 | Viewed by 1574

Abstract

Recent advancements in nanotechnology have improved the application of copper oxide (CuO) nanostructures, known for their diverse antibacterial, electrical, catalytic, optical, and pharmacological properties, which depend on nanoparticle morphology. This study investigated two synthesis methods for structured CuO: microwave-assisted hydrolysis and ultrasound using [...] Read more.

Recent advancements in nanotechnology have improved the application of copper oxide (CuO) nanostructures, known for their diverse antibacterial, electrical, catalytic, optical, and pharmacological properties, which depend on nanoparticle morphology. This study investigated two synthesis methods for structured CuO: microwave-assisted hydrolysis and ultrasound using copper acetate and KOH, and an eco-friendly method involving cholesterol-free egg white albumin and Solanum lycopersicum extract. Characterization techniques, including XRD, FTIR, and SEM-EDS, were utilized to analyze the produced CuO. XRD confirmed high-purity monoclinic CuO structures in the sample obtained via the chemical method, while characteristic peaks of tenorite and dolerophanite were observed in the albumin-synthesized sample. ATR-FTIR analysis revealed O-H stretching bands around 3400 cm⁻¹, indicating adsorbed H-OH or -OH and strong Cu-O bond peaks at 434 cm⁻¹. The CuO synthesized via microwave and ultrasound methods displayed superior crystallinity compared to commercial CuO. SEM illustrated various morphologies, such as flakes, microspheres, and irregular polyhedra, influenced by the presence of proteins and organic acids. Antibacterial tests demonstrated the effective inhibition of Escherichia coli and Enterococcus faecalis, confirming the potential of CuO as a promising antibacterial agent. Overall, the findings highlight the effectiveness of green chemistry in developing crystalline CuO for various applications. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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30 pages, 11520 KiB

Open AccessEditor’s ChoiceReview

Progress in Tungsten Trioxide-Based Materials for Energy Storage and Smart Window Applications

by Khursheed Ahmad and Tae Hwan Oh

Crystals 2025, 15(1), 10; https://doi.org/10.3390/cryst15010010 - 25 Dec 2024

Cited by 1 | Viewed by 1072

Abstract

Previous years have witnessed a rapid surge in WO₃-based experimental reports for the construction of energy storage devices (ESDs) and electrochromic devices (ECDs). WO₃ is a highly electrochromic (EC) material with a wide band gap that has been extensively used [...] Read more.

Previous years have witnessed a rapid surge in WO₃-based experimental reports for the construction of energy storage devices (ESDs) and electrochromic devices (ECDs). WO₃ is a highly electrochromic (EC) material with a wide band gap that has been extensively used for the construction of working electrodes for supercapacitor (SC) and ECD applications. Previously, WO₃-based hybrid composites were explored for SC and ECD applications. In this review report, we have compiled the WO₃-based hybrid electrode materials for SC and ECD applications. It is believed that the present review would benefit the researchers working on the fabrication of electrode materials for SC and ECD applications. In this review article, challenges and future perspectives have been discussed for the development of WO₃-based SCs and ECDs. Full article

(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization (2nd Edition))

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12 pages, 3272 KiB

Open AccessEditor’s ChoiceArticle

Microstructural Evolution and Thermal Stability of Long Period Stacking Ordered Phases in Mg₉₇Er₂Ni₁ and Mg₉₇Er₂Zn₁ Alloys

by Jian Yin, Yushun Liu and Guo-Zhen Zhu

Crystals 2024, 14(12), 1092; https://doi.org/10.3390/cryst14121092 - 19 Dec 2024

Viewed by 938

Abstract

The influence of transition metals (Ni and Zn) on the formation, morphology, and thermal stability of long-period stacking ordered (LPSO) phases in Mg₉₇Er₂N_i1 and Mg₉₇Er₂Zn₁ alloys was investigated. In the as-cast state, both [...] Read more.

The influence of transition metals (Ni and Zn) on the formation, morphology, and thermal stability of long-period stacking ordered (LPSO) phases in Mg₉₇Er₂N_i1 and Mg₉₇Er₂Zn₁ alloys was investigated. In the as-cast state, both alloys consist of α-Mg and LPSO phases. Heat treatment at 540 °C for 20 h dissolves block-like and lamellar LPSO phases into the α-Mg matrix in the Mg₉₇Er₂Zn₁ alloy, with lamellar LPSO phases reprecipitating during subsequent cooling from 540 °C to 400 °C. Comparative analysis shows that Ni significantly enhances the thermal stability of the LPSO phase compared to Zn. Ni favors the formation of block-shaped LPSO phases, while Zn facilitates lamellar LPSO precipitation within the α-Mg matrix. The LPSO phase in the Mg₉₇Er₂Ni₁ alloy exhibits an exceptionally high melting temperature of 605 °C, the highest reported for an LPSO phase. Additionally, heat treatment at 500 °C for 100 h preserves the area fraction of the LPSO phase in the Mg₉₇Er₂Ni₁ alloy, and at 540 °C for 100 h, the LPSO grains grow without phase dissolution or structural transformation of their 18R-type configuration. These findings provide valuable insights into the role of alloying transition metal elements in controlling the stability and morphology of LPSO phases, offering pathways for tailoring the morphology of the LPSO phase in the Mg-based alloys. Full article

(This article belongs to the Special Issue Advances in Metal Matrix Composites: Structure, Properties and Applications)

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16 pages, 8895 KiB

Open AccessEditor’s ChoiceArticle

Study on the Alleviation of Performance Degradation and Voltage Stability of PEMFC by Adding Silica Under Low-Temperature and Low-Humidity Conditions

by Qiang Bai, Chuangyu Hsieh, Zhenghong Liu, Qipeng Chen and Fangbor Weng

Crystals 2024, 14(12), 1089; https://doi.org/10.3390/cryst14121089 - 18 Dec 2024

Cited by 1 | Viewed by 865

Abstract

This study enhances PEMFC performance at low temperature and low humidity by incorporating hydrophilic inorganic silica materials inside the PEMFC. Firstly, the polarization performance of the cell under varying humidity levels was investigated using a controlled variable method. Secondly, the power stability of [...] Read more.

This study enhances PEMFC performance at low temperature and low humidity by incorporating hydrophilic inorganic silica materials inside the PEMFC. Firstly, the polarization performance of the cell under varying humidity levels was investigated using a controlled variable method. Secondly, the power stability of the PEMFC was examined by observing voltage stability under constant current. Finally, the cell’s transient response at startup was studied. Experimental results indicate that the addition of silica partially mitigates the significant performance decline of the cell under a high humidity range (100% RH–50% RH). However, the effect is relatively average in a low humidity range (50% RH–20% RH). Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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31 pages, 15017 KiB

Open AccessEditor’s ChoiceArticle

Green Synthesized Composite AB-Polybenzimidazole/TiO₂ Membranes with Photocatalytic and Antibacterial Activity

by Hristo Penchev, Katerina Zaharieva, Silvia Dimova, Ivelina Tsacheva, Rumyana Eneva, Stephan Engibarov, Irina Lazarkevich, Tsvetelina Paunova-Krasteva, Maria Shipochka, Ralitsa Mladenova, Ognian Dimitrov, Daniela Stoyanova and Irina Stambolova

Crystals 2024, 14(12), 1081; https://doi.org/10.3390/cryst14121081 - 16 Dec 2024

Viewed by 1324

Abstract

Novel AB-Polybenzimidazole (AB-PBI)/TiO₂ nanocomposite membranes have been prepared using a synthetic green chemistry approach. Modified Eaton’s reagent (methansulfonic acid/P₂O₅) was used as both reaction media for microwave-assisted synthesis of AB-PBI and as an efficient dispersant of partially agglomerated [...] Read more.

Novel AB-Polybenzimidazole (AB-PBI)/TiO₂ nanocomposite membranes have been prepared using a synthetic green chemistry approach. Modified Eaton’s reagent (methansulfonic acid/P₂O₅) was used as both reaction media for microwave-assisted synthesis of AB-PBI and as an efficient dispersant of partially agglomerated titanium dioxide powders. Composite membranes of 80 µm thickness have been prepared by a film casting approach involving subsequent anti-solvent inversion in order to obtain porous composite membranes possessing high sorption capacity. The maximal TiO₂ filler content achieved was 20 wt.% TiO₂ nanoparticles (NPs). Titania particles were green synthesized (using a different content of Mentha Spicata (MS) aqueous extract) by hydrothermal activation (150 °C), followed by thermal treatment at 400 °C. The various methods such as powder X-ray diffraction and Thermogravimetric analyses, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and Energy-dispersive X-ray spectroscopy, Electronic paramagnetic resonance, Scanning Electron Microscopy and Transmission Electron Microscopy have been used to study the phase and surface composition, structure, morphology, and thermal behavior of the synthesized nanocomposite membranes. The photocatalytic ability of the so-prepared AB-Polybenzimidazole/bio-TiO₂ membranes was studied for decolorization of Reactive Black 5 (RB5) as a model azo dye pollutant under UV light illumination. The polymer membrane in basic form, containing TiO₂ particles, was obtained with a 40 mL quantity of the MS extract, exhibiting the highest decolorization rate (96%) after 180 min of UV irradiation. The so-prepared AB-Polybenzimidazole/TiO₂ samples have a powerful antibacterial effect on E. coli when irradiated by UV light. Full article

(This article belongs to the Special Issue Photocatalysis and Targeted Sorbent Activity of Advanced Polymer-Based Composites)

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12 pages, 4142 KiB

Open AccessEditor’s ChoiceArticle

Batch Cooling Crystallization of a Model System Using Direct Nucleation Control and High-Performance In Situ Microscopy

by Josip Budimir Sacher, Nenad Bolf and Marko Sejdić

Crystals 2024, 14(12), 1079; https://doi.org/10.3390/cryst14121079 - 13 Dec 2024

Cited by 1 | Viewed by 1378

Abstract

The aim of this study was to investigate the use of automated high performance in situ microscopy (HPM) for monitoring and direct nucleation control (DNC) during cooling crystallization. Compared to other techniques, HPM enables the detection of small crystals in the range of [...] Read more.

The aim of this study was to investigate the use of automated high performance in situ microscopy (HPM) for monitoring and direct nucleation control (DNC) during cooling crystallization. Compared to other techniques, HPM enables the detection of small crystals in the range of 1 to 10 μm. Therefore, a novel DNC-controlled variable was investigated to determine the potential improvement of the method. The laboratory system and process control software were developed in-house. A well-studied crystallization model system, the seeded batch cooling crystallization of α-glycine from water, was investigated under normal conditions and temperatures below 60 °C. It was postulated that length-weighted edge-to-edge counts in the range of 1 to 10 μm would be most sensitive to the onset of secondary nucleation and are therefore, used as a control variable. Linear cooling experiments were conducted to determine the initial setpoint for the DNC experiments. Three DNC experiments were then performed with different setpoints and an upper and lower counts limit. It was found that the DNC method can be destabilized with a low setpoint and narrow counts limits. In addition, the new controlled variable is highly sensitive to the formation of bubbles at the microscope window and requires careful evaluation. To address the advantages of the DNC method, an additional linear cooling experiment of the same duration was performed, and it was found that the DNC method resulted in a larger average crystal size. Overall, it can be concluded that the HPM method is suitable for DNC control and could be improved by modifying the image processing algorithm. Full article

(This article belongs to the Special Issue Crystallization Process and Simulation Calculation, Third Edition)

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17 pages, 11260 KiB

Open AccessEditor’s ChoiceArticle

Surface Cladding of Mild Steel Coated with Ni Containing TiO₂ Nanoparticles Using a High-Temperature Arc from TIG Welding

by Kavian O. Cooke, Ayesha Mirza, Junlin Chen and Alaa Al Hausone

Crystals 2024, 14(12), 1048; https://doi.org/10.3390/cryst14121048 - 30 Nov 2024

Viewed by 988

Abstract

This study explores the use of a high-temperature arc generated during tungsten inert gas (TIG) welding to enhance the mechanical properties of the surface of AISI 1020 steel. An innovative two-step process involves using the high-temperature arc as an energy source to fuse [...] Read more.

This study explores the use of a high-temperature arc generated during tungsten inert gas (TIG) welding to enhance the mechanical properties of the surface of AISI 1020 steel. An innovative two-step process involves using the high-temperature arc as an energy source to fuse a previously electrodeposited Ni/TiO₂ coating to the surface of the substrate. The cladded surface is characterised by a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), an optical microscope (O.M.) equipped with laser-induced breakdown spectroscopy (LIBS), Vicker’s microhardness testing, and pin-on-plate wear testing. The treated surface exhibits a unique amalgamation of hardening mechanisms, including nanoparticle dispersion strengthening, grain size reduction, and solid solution strengthening. The thickness of the electrodeposited layer appears to strongly influence the hardness variation across the width of the treated layer. The hardness of the treated layer when the Ni coating contains 30 nm TiO₂ particles was found to be 451 VHN, validating an impressive 2.7-fold increase in material hardness compared to the untreated substrate (165 VHN). Similarly, the treated surface exhibits a twofold improvement in wear resistance (9.0 × 10² µm³/s), making it substantially more durable in abrasive environments than the untreated surface. Microstructural and EDS analysis reveal a significant reduction in grain size and the presence of high concentrations of Ni and TiO₂ within the treated region, providing clear evidence for the activation of several strengthening mechanisms. Full article

(This article belongs to the Special Issue Advances in Surface Modifications of Metallic Materials)

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15 pages, 290 KiB

Open AccessEditor’s ChoiceReview

A Survey of Crystals for SPECT Imaging

by Shuyu Xu, Zijun Yan and Qingyang Wei

Crystals 2024, 14(12), 1039; https://doi.org/10.3390/cryst14121039 - 29 Nov 2024

Cited by 2 | Viewed by 1468

Abstract

Single-photon emission computed tomography (SPECT) is an important nuclear medicine imaging tool for diagnosis and drug research. The gamma-ray detector is the core component of the SPECT system and influences the overall system performance. The detector crystals, which can be divided into scintillation [...] Read more.

Single-photon emission computed tomography (SPECT) is an important nuclear medicine imaging tool for diagnosis and drug research. The gamma-ray detector is the core component of the SPECT system and influences the overall system performance. The detector crystals, which can be divided into scintillation crystals and semiconductor crystals, are among the main determinants of the detector’s performance. The development of these crystal materials plays an important role in improving SPECT imaging. This paper provides a survey of the technological development and applications of several crystals currently used in SPECT detectors. Furthermore, it explores future research directions for the development of detector crystals. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

17 pages, 2970 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of New Organoammonium, Thiazolium, and Pyridinium Triiodide Salts: Crystal Structures, Polymorphism, and Thermal Stability

by Madhushi Bandara, Khadijatul Kobra, Spencer R. Watts, Logan Grady, Connor Hudson, Claudina Veas, Timothy W. Hanks, Rakesh Sachdeva, Jorge Barroso, Colin D. McMillen and William T. Pennington

Crystals 2024, 14(12), 1020; https://doi.org/10.3390/cryst14121020 - 25 Nov 2024

Viewed by 1286

Abstract

Triiodide salts are of interest for a variety of applications, including but not limited to electrochemical and photochemical devices, as antimicrobials and disinfectants, in supramolecular chemistry and crystal engineering, and in ionic liquids and deep eutectic solvents. Our work has focused on the [...] Read more.

Triiodide salts are of interest for a variety of applications, including but not limited to electrochemical and photochemical devices, as antimicrobials and disinfectants, in supramolecular chemistry and crystal engineering, and in ionic liquids and deep eutectic solvents. Our work has focused on the design of salt–solvate cocrystals and deep eutectic solvents in which the triiodide anion interacts as a halogen bond acceptor with organoiodine molecules. To understand structure–property relationships in these hybrid materials, it is essential to have benchmark structural and physical data for the parent triiodide salt component. Herein, we report the structure and thermal properties of eight new triiodide salts, three of which exhibit polymorphism: tetrapentylammonium triiodide (1a and 1b), tetrahexylammonium triiodide (2), trimethylphenylammonium triiodide (3), trimethylbenzylammonium triiodide (4), triethylbenzylammonium triiodide (5), tri-n-butylbenzylammonium triiodide (6), 3-methylbenzothizolium triiodide (7a and 7b), and 2-chloro-1-methylpyridinium triiodide (8a and 8b). The structural features of the triiodide anion, Raman spectroscopic analysis, and melting and thermal decomposition behavior of the salts, as well as a computational analysis of the polymorphs, are discussed. The polymorphic pairs here are distinguished by symmetric versus asymmetric triiodide anions, as well as different packing patterns. Computational analyses revealed more subtle differences in their isosurface plots. Importantly, this study provides reference data for these new triiodide salts for comparison to hybrid cocrystals and deep eutectic solvents formed from their combination with various organoiodines. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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16 pages, 4032 KiB

Open AccessEditor’s ChoiceArticle

In Situ Microscopy with Real-Time Image Analysis Enables Online Monitoring of Technical Protein Crystallization Kinetics in Stirred Crystallizers

by Julian Mentges, Daniel Bischoff, Brigitte Walla and Dirk Weuster-Botz

Crystals 2024, 14(12), 1009; https://doi.org/10.3390/cryst14121009 - 21 Nov 2024

Cited by 2 | Viewed by 1715

Abstract

Controlling protein crystallization processes is essential for improving downstream processing in biotechnology. This study investigates the combination of machine learning-based image analysis and in situ microscopy for real-time monitoring of protein crystallization kinetics. The experimental research is focused on the batch crystallization of [...] Read more.

Controlling protein crystallization processes is essential for improving downstream processing in biotechnology. This study investigates the combination of machine learning-based image analysis and in situ microscopy for real-time monitoring of protein crystallization kinetics. The experimental research is focused on the batch crystallization of an alcohol dehydrogenase from Lactobacillus brevis (LbADH) and two selected rational crystal contact mutants. Technical protein crystallization experiments were performed in a 1 L stirred crystallizer by adding polyethyleneglycol 550 monomethyl ether (PEG 550 MME). The estimated crystal volumes from online microscopy correlated well with the offline measured protein concentrations in solution. In addition, in situ microscopy was superior to offline data if amorphous protein precipitation occurred. Real-time image analysis provides the data basis for online estimation of important batch crystallization performance indicators like yield, crystallization kinetics, crystal size distributions, and number of protein crystals. Surprisingly, one of the LbADH mutants, which should theoretically crystallize more slowly than the wild type based on molecular dynamics (MD) simulations, showed better crystallization performance except for the yield. Thus, online monitoring of scalable protein crystallization processes with in situ microscopy and real-time image analysis improves the precision of crystallization studies for industrial settings by providing comprehensive data, reducing the limitations of traditional analytical techniques, and enabling new insights into protein crystallization process dynamics. Full article

(This article belongs to the Section Biomolecular Crystals)

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14 pages, 4748 KiB

Open AccessEditor’s ChoiceArticle

Growth and Characterization of High-Quality YTiO₃ Single Crystals: Minimizing Ti⁴⁺ Containing Impurities and TiN Formation

by Yong Liu, David Wenhua Bi and Arnaud Magrez

Crystals 2024, 14(11), 989; https://doi.org/10.3390/cryst14110989 - 16 Nov 2024

Cited by 1 | Viewed by 986

Abstract

We report the growth of YTiO₃ single crystals using different starting materials with the nominal compositions, (1) stoichiometric YTiO₃; (2) oxygen deficient YTiO_2.925; (3) oxygen deficient YTiO_2.85, and different atmospheres, (1) 97%Ar/3%H₂; (2) Ar; [...] Read more.

We report the growth of YTiO₃ single crystals using different starting materials with the nominal compositions, (1) stoichiometric YTiO₃; (2) oxygen deficient YTiO_2.925; (3) oxygen deficient YTiO_2.85, and different atmospheres, (1) 97%Ar/3%H₂; (2) Ar; (3) forming gas 95%N₂/5%H₂, using the laser floating zone growth technique. The oxygen-deficient starting materials were prepared by mixing Y₂O₃, Ti₂O₃, and Ti powder according to the YTiO_3-δ stoichiometry. The addition of Ti powder to the starting materials effectively reacts with the oxygen in the floating zone furnace chamber, reducing Ti⁴⁺ ion-containing impurities. High-quality YTiO₃ single crystals with (2 0 0) facet were grown from the starting materials corresponding to the nominal composition YTiO_2.925. YTiO₃ single crystals grown from different starting materials are characteristic of oxygen content of 3 in both pure crystals and crystals containing impurities, revealed by the same oxygen occupancy in single crystal X-ray diffraction measurements. When forming gas was used, a golden TiN coating formed on the surface of rod. Full article

(This article belongs to the Special Issue Advances in Crystal Growth: Pioneering Materials for Tomorrow's Technologies)

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17 pages, 10195 KiB

Open AccessEditor’s ChoiceArticle

In Situ Synthesis of NPC-Cu₂O/CuO/rGO Composite via Dealloying and Microwave-Assisted Hydrothermal Technique

by Mircea Nicolaescu, Sebastian Ambrus, Petru Hididis, Mina Morariu (Popescu), Iosif Hulka, Corina Orha, Carmen Lazau, Cosmin Codrean and Cornelia Bandas

Crystals 2024, 14(11), 968; https://doi.org/10.3390/cryst14110968 - 8 Nov 2024

Cited by 1 | Viewed by 1570

Abstract

The nanoporous copper (NPC)-copper oxides (Cu₂O/CuO)/reduced graphene oxide (rGO) composite structure was synthesized by combining the dealloying process of Cu₄₈Zr₄₇Al₅ amorphous ribbons with a microwave-assisted hydrothermal technique at a temperature of 200 °C. The main advantage [...] Read more.

The nanoporous copper (NPC)-copper oxides (Cu₂O/CuO)/reduced graphene oxide (rGO) composite structure was synthesized by combining the dealloying process of Cu₄₈Zr₄₇Al₅ amorphous ribbons with a microwave-assisted hydrothermal technique at a temperature of 200 °C. The main advantage of the microwave-assisted hydrothermal process is the oxidation of nanoporous copper together with the in situ reduction of graphene oxide to form rGO. The integration of rGO with NPC improves electrical conductivity and streamlines the process of electron transfer. This composite exhibit considerable potential in electrochemical catalysis application, due to the combined catalytic activity of NPC and the chemical reactivity of rGO. Our study relates the transition to n-type rGO in microwave-assisted hydrothermal reactions, and also the development of an electrode material suitable for electrochemical applications based on the p-p-n junction NPC-Cu₂O/CuO/rGO heterostructure. To confirm the formation of the composite structure, structural, morphological, and optical techniques as XRD, SEM/EDX, UV-Vis and Raman spectroscopy were used. The composite’s electrochemical properties were measured by EIS and Mott-Schottky analyses, showing a charge transfer resistance (Rp) of 250 Ω and indicating the type of the semiconductor properties. The calculated carrier densities of 4.2 × 10¹⁸ cm⁻³ confirms n-type semiconductor characteristic for rGO, and 7.22 × 10¹⁸ cm⁻³ for Cu₂O/CuO indicating p-type characteristic. Full article

(This article belongs to the Section Hybrid and Composite Crystalline Materials)

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14 pages, 3865 KiB

Open AccessEditor’s ChoiceArticle

Assessment of Classical Force-Fields for Graphene Mechanics

by Zhiwei Ma, Yongkang Tan, Xintian Cai, Xue Chen, Tan Shi, Jianfeng Jin, Yifang Ouyang and Qing Peng

Crystals 2024, 14(11), 960; https://doi.org/10.3390/cryst14110960 - 2 Nov 2024

Cited by 2 | Viewed by 1458

Abstract

The unique properties of graphene have attracted the interest of researchers from various fields, and the discovery of graphene has sparked a revolution in materials science, specifically in the field of two-dimensional materials. However, graphene synthesis’s costly and complex process significantly impairs researchers’ [...] Read more.

The unique properties of graphene have attracted the interest of researchers from various fields, and the discovery of graphene has sparked a revolution in materials science, specifically in the field of two-dimensional materials. However, graphene synthesis’s costly and complex process significantly impairs researchers’ endeavors to explore its properties and structure experimentally. Molecular dynamics simulation is a well-established and useful tool for investigating graphene’s atomic structure and dynamic behavior at the nanoscale without requiring expensive and complex experiments. The accuracy of the molecular dynamics simulation depends on the potential functions. This work assesses the performance of various potential functions available for graphene in mechanical properties prediction. The following two cases are considered: pristine graphene and pre-cracked graphene. The most popular fifteen potentials have been assessed. Our results suggest that diverse potentials are suitable for various applications. REBO and Tersoff potentials are the best for simulating monolayer pristine graphene, and the MEAM and the AIREBO-m potentials are recommended for those with crack defects because of their respective utilization of the electron density and inclusion of the long-range interaction. We recommend the AIREBO-m potential for a general case of classical molecular dynamics study. This work might help to guide the selection of potentials for graphene simulations and the development of further advanced interatomic potentials. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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17 pages, 9453 KiB

Open AccessEditor’s ChoiceReview

Progress and Prospect of Liquid Crystal Droplets

by Le Zhou, Tingjun Zhong, Huihui Wang, Ke Xu, Pouya Nosratkhah and Kristiaan Neyts

Crystals 2024, 14(11), 934; https://doi.org/10.3390/cryst14110934 - 29 Oct 2024

Cited by 1 | Viewed by 2304

Abstract

Liquid crystal (LC) droplets are highly attractive for applications in privacy windows, optical switches, optical vortices, optical microresonators, microlenses, and biosensors due to their ease of fabrication and easy alignment at surfaces. This review presents the latest advancements in LC droplets, which have [...] Read more.

Liquid crystal (LC) droplets are highly attractive for applications in privacy windows, optical switches, optical vortices, optical microresonators, microlenses, and biosensors due to their ease of fabrication and easy alignment at surfaces. This review presents the latest advancements in LC droplets, which have nematic, chiral nematic, and twist–bend nematic and ferroelectric nematic phases, or blue phases. Finally, it discusses the challenges and opportunities for applications based on LC droplets. The main challenges encompass the precise control of internal structures and defects to meet diverse application requirements, enhancing stability and durability across various environments, reducing large-scale production costs to improve commercial feasibility, increasing response speeds to external stimuli to adapt to rapidly changing scenarios, and developing tunable LC droplets to achieve broader functionalities. Full article

(This article belongs to the Special Issue Liquid Crystal Materials and Devices)

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9 pages, 2324 KiB

Open AccessEditor’s ChoiceArticle

Electrochemical Properties of Ultrathin LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111) Slurry-Cast Li-Ion Battery

by Byoung-Nam Park

Crystals 2024, 14(10), 882; https://doi.org/10.3390/cryst14100882 - 10 Oct 2024

Cited by 2 | Viewed by 1730

Abstract

In thin LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111) electrodes, pseudocapacitive behavior is notably enhanced due to their increased surface-to-volume ratio, which intensifies the role of the electrode–electrolyte interface. This behavior is driven by fast, reversible redox reactions and ion intercalation [...] Read more.

In thin LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111) electrodes, pseudocapacitive behavior is notably enhanced due to their increased surface-to-volume ratio, which intensifies the role of the electrode–electrolyte interface. This behavior is driven by fast, reversible redox reactions and ion intercalation occurring near the surface, where the shorter diffusion path allows for more efficient ionic transport. The reduced thickness of the electrodes shortens the Li-ion diffusion distance, improving the diffusion coefficient by a factor of 40 compared to thicker electrodes, where ion transport is hindered by longer diffusion paths. The increased surface area and shorter diffusion paths promote faster electrochemical kinetics, allowing for quicker ion intercalation and deintercalation processes. The thin-film configuration enhances pseudocapacitive charge storage, which is essential for applications requiring rapid charge and discharge cycles. As a result, the combination of improved Li-ion diffusion and enhanced surface activity contributes to superior electrochemical performance, offering higher power densities, faster energy delivery, and better rate capability. This improvement in performance makes thin NMC111 electrodes particularly advantageous for applications such as high-power energy storage systems, where fast kinetics and high power densities are critical. These findings highlight the importance of interface engineering and material morphology in optimizing the performance of Li-ion batteries and similar electrochemical energy storage devices. Full article

(This article belongs to the Section Materials for Energy Applications)

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17 pages, 9494 KiB

Open AccessEditor’s ChoiceArticle

Influences of Zr and V Addition on the Crystal Chemistry of θ-Al₁₃Fe₄ and the Grain Refinement of α-Al in an Al-4Fe Alloy Based on Experiment and First-Principle Calculations

by Zhongping Que, Changming Fang, Junhai Xia and Zhongyun Fan

Crystals 2024, 14(10), 879; https://doi.org/10.3390/cryst14100879 - 9 Oct 2024

Cited by 1 | Viewed by 1282

Abstract

Fe-containing intermetallic compounds (IMCs) are among the most detrimental second phases in aluminum alloys. One particularly harmful type is θ-Al₁₃Fe₄, which exhibits a needle- or plate-like morphology, leading to greater degradation of mechanical properties compared to other Fe-IMCs with [...] Read more.

Fe-containing intermetallic compounds (IMCs) are among the most detrimental second phases in aluminum alloys. One particularly harmful type is θ-Al₁₃Fe₄, which exhibits a needle- or plate-like morphology, leading to greater degradation of mechanical properties compared to other Fe-IMCs with more compact structures, such as α-Al₁₅(Fe,Mn)₃Si₂. The addition of alloying elements is a crucial strategy for modifying the microstructure during the solidification process of aluminum alloys. This study investigates the effects of adding vanadium (V) and zirconium (Zr) on the morphology and crystal chemistry of θ-Al₁₃Fe₄ in an Al-4Fe alloy, employing a combination of experimental observations, first-principle calculations, and thermodynamic analysis. Our findings indicate that zirconium significantly refines both the primary θ-Al₁₃Fe₄ particles and the α-Al grains. Additionally, a small amount of vanadium can be incorporated into one of the Wyckoff 4i Al sites in θ-Al₁₃Fe₄, rather than occupying any Fe sites, under casting conditions, in addition to the formation of binary Al-V phases. Full article

(This article belongs to the Special Issue Microstructure and Properties of Intermetallic Compounds)

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15 pages, 11097 KiB

Open AccessEditor’s ChoiceArticle

Structural Analysis of Coordination Cage/Guest Complexes Prepared with the ‘Crystalline Sponge’ Methodology

by Christopher G. P. Taylor, James R. Williams, Stephen P. Argent and Michael D. Ward

Crystals 2024, 14(10), 873; https://doi.org/10.3390/cryst14100873 - 2 Oct 2024

Cited by 1 | Viewed by 1534

Abstract

The crystalline sponge method has proven invaluable in the preparation and analysis of supramolecular host/guest complexes if the host can be obtained in a suitable crystalline form, allowing the analysis of guest binding modes inside host cavities which can inform other studies into [...] Read more.

The crystalline sponge method has proven invaluable in the preparation and analysis of supramolecular host/guest complexes if the host can be obtained in a suitable crystalline form, allowing the analysis of guest binding modes inside host cavities which can inform other studies into processes such as catalysis. Here, we report the structures of a set of ten host/guest complexes using an octanuclear coordination cage host with a range of small-molecule neutral organic guests including four aromatic aldehydes and ketones, three cyclic lactams, and three epoxides. In all cases, the cavity-bound guests are anchored by a collection of CH•••O hydrogen-bonding interactions between an O atom on the guest and a convergent set of CH protons at a pocket on the cage interior surface. Depending on guest size and the presence of solvent molecules as additional guests, there may be one or two cavity-bound guests, with small aromatic guests forming π-stacked pairs. Some guests (the lactams) participate in additional NH•••F H-bonding interactions with surface-bound fluoroborate anions, which indicate the type of anion/guest interactions thought to be responsible for solution-phase catalytic reactions of bound guests. Full article

(This article belongs to the Section Macromolecular Crystals)

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24 pages, 31908 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Textured 0.685(Na_0.5Bi_0.5)TiO₃-0.065BaTiO₃-0.25SrTiO₃ Electrostrictive Ceramics by Templated Grain Growth Using NaNbO₃ Templates and Characterization of Their Electrical Properties

by Kiran Andleeb, Doan Thanh Trung, John G. Fisher, Tran Thi Huyen Tran, Jong-Sook Lee, Woo-Jin Choi and Wook Jo

Crystals 2024, 14(10), 861; https://doi.org/10.3390/cryst14100861 - 30 Sep 2024

Viewed by 1546

Abstract

Electrostrictive materials based on (Na_0.5Bi_0.5)TiO₃ are promising lead-free candidates for high-precision actuation applications, yet their properties require further improvement. This study aims to enhance the electromechanical properties of a predominantly electrostrictive composition, 0.685(Na_0.5Bi_0.5)TiO₃ [...] Read more.

Electrostrictive materials based on (Na_0.5Bi_0.5)TiO₃ are promising lead-free candidates for high-precision actuation applications, yet their properties require further improvement. This study aims to enhance the electromechanical properties of a predominantly electrostrictive composition, 0.685(Na_0.5Bi_0.5)TiO₃-0.065BaTiO₃-0.25SrTiO₃, by using templated grain growth. Textured ceramics were prepared with 1~9 wt% NaNbO₃ templates. A high Lotgering factor of 95% was achieved with 3 wt% templates and sintering at 1200 °C for 12 h. Polarization and strain hysteresis loops confirmed the ergodic nature of the system at room temperature, with unipolar strain significantly improving from 0.09% for untextured ceramics to 0.23% post-texturing. A maximum normalized strain, S_max/E_max (d₃₃*), of 581 pm/V was achieved at an electric field of 4 kV/mm for textured ceramics. Textured ceramics also showed enhanced performance over untextured ceramics at lower electric fields. The electrostrictive coefficient Q₃₃ increased from 0.017 m⁴C⁻² for untextured ceramics to 0.043 m⁴C⁻² for textured ceramics, accompanied by reduced strain hysteresis, making the textured 0.685(Na_0.5Bi_0.5)TiO₃-0.065BaTiO₃-0.25SrTiO₃ composition suitable for high-precision actuation applications. Dielectric properties measured between −193 °C and 550 °C distinguished the depolarization, Curie–Weiss and Burns temperatures, and activation energies for polar nanoregion transitions and dc conduction. Dispersive dielectric constants were found to observe the “two” law exhibiting a temperature dependence double the value of the Curie–Weiss constant, with shifts of about 10 °C per frequency decade where the non-dispersive THz limit was identified. Full article

(This article belongs to the Special Issue Advanced Ferroelectric, Piezoelectric and Dielectric Ceramics)

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18 pages, 3414 KiB

Open AccessEditor’s ChoiceArticle

Crystallographic Studies on Non-Covalent Interactions in Aryl-Substituted Antimony Organometallics

by Ana Torvisco, Melanie Wolf, Roland C. Fischer and Frank Uhlig

Crystals 2024, 14(10), 860; https://doi.org/10.3390/cryst14100860 - 29 Sep 2024

Viewed by 1337

Abstract

A series of novel and previously published organoantimony compounds (R_nSbX_3−n, X = Cl, Br; R = o-tolyl, 2,6-xylyl, 1-naphthyl, and 9-anthracenyl), were synthesized and characterized. In addition, single-crystal X-ray diffraction was employed to elucidate the molecular structures of [...] Read more.

A series of novel and previously published organoantimony compounds (R_nSbX_3−n, X = Cl, Br; R = o-tolyl, 2,6-xylyl, 1-naphthyl, and 9-anthracenyl), were synthesized and characterized. In addition, single-crystal X-ray diffraction was employed to elucidate the molecular structures of all solid species. These compounds display non-covalent intermolecular interactions in the form of edge-to-face, π···π stacking, and CH₃···π interactions, and the effects of the substituent type and substituent bulk on the nature of these interactions present will be highlighted and discussed. Full article

(This article belongs to the Section Crystal Engineering)

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29 pages, 9007 KiB

Open AccessEditor’s ChoiceReview

The Role of Liquid Crystal Elastomers in Pioneering Biological Applications

by Faeze Shiralipour, Yeganeh Nik Akhtar, Ashley Gilmor, Gisele Pegorin, Abraham Valerio-Aguilar and Elda Hegmann

Crystals 2024, 14(10), 859; https://doi.org/10.3390/cryst14100859 - 29 Sep 2024

Cited by 2 | Viewed by 3652

Abstract

Liquid crystal elastomers have shown an attractive potential for various biological applications due to their unique combination of mechanical flexibility and responsiveness to external stimuli. In this review, we will focus on a few examples of LCEs used with specific applications for biological/biomedical/environmental [...] Read more.

Liquid crystal elastomers have shown an attractive potential for various biological applications due to their unique combination of mechanical flexibility and responsiveness to external stimuli. In this review, we will focus on a few examples of LCEs used with specific applications for biological/biomedical/environmental systems. So far, areas of innovation have been concentrating on the integration of LCEs to enhance stability under physiological conditions, ensure precise integration with biological systems, and address challenges related to optical properties and spatial control of deformation. However, several challenges and limitations must still be addressed to fully realize their potential in biomedical and environmental fields, and future research should focus on continuing to improve biocompatibility, response to the environment and chemical cues, mechanical properties, ensuring long-term stability, and establishing cost-effective production processes. So far, 3D/4D printing appears as a great promise to develop materials of high complexity, almost any shape, and high production output. However, researchers need to find ways to reduce synthesis costs to ensure that LCEs are developed using cost-effective production methods at a scale necessary for their specific applications’ needs. Full article

(This article belongs to the Special Issue Liquid Crystal Research and Novel Applications in the 21st Century)

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19 pages, 3747 KiB

Open AccessEditor’s ChoiceArticle

Ductility Index for Refractory High Entropy Alloys

by Ottó K. Temesi, Lajos K. Varga, Nguyen Quang Chinh and Levente Vitos

Crystals 2024, 14(10), 838; https://doi.org/10.3390/cryst14100838 - 27 Sep 2024

Cited by 2 | Viewed by 1646

Abstract

The big advantage of refractory high entropy alloys (RHEAs) is their strength at high temperatures, but their big disadvantage is their brittleness at room temperature, which prevents their machining. There is a great need to classify the alloys in terms of brittle-ductile (B-D) [...] Read more.

The big advantage of refractory high entropy alloys (RHEAs) is their strength at high temperatures, but their big disadvantage is their brittleness at room temperature, which prevents their machining. There is a great need to classify the alloys in terms of brittle-ductile (B-D) properties, with easily obtainable ductility indices (DIs) ready to help design these refractory alloys. Usually, the DIs are checked by representing them as a function of fraction strain, ε. The critical values of DI and ε divide the DI—ε area into four squares. In the case of a successful DI, the points representing the alloys are located in the two diagonal opposite squares, well separating the alloys with (B-D) properties. However, due to the scatter of the data, the B-D separation is not perfect, and it is difficult to establish the critical value of DI. In this paper, we solve this problem by replacing the fracture strain parameter with new DIs that scale with the old DIs. These new DIs are based on the force constant and amplitude of thermal vibration around the Debye temperature. All of them are easily available and can be calculated from tabulated data. Full article

(This article belongs to the Special Issue Advances in Processing, Simulation and Characterization of Alloys)

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16 pages, 323 KiB

Open AccessEditor’s ChoiceArticle

Three-Dimensional and Two-Dimensional Green Tensors of Piezoelectric Quasicrystals

by Markus Lazar and Eleni Agiasofitou

Crystals 2024, 14(10), 835; https://doi.org/10.3390/cryst14100835 - 26 Sep 2024

Cited by 3 | Viewed by 1619

Abstract

In this work, within the framework of the linear piezoelectricity theory of quasicrystals, the three-dimensional and two-dimensional Green tensors for arbitrary piezoelectric quasicrystals are derived. In the piezoelectricity of quasicrystals, where phonon, phason and electric fields exist, we introduce the corresponding multifields by [...] Read more.

In this work, within the framework of the linear piezoelectricity theory of quasicrystals, the three-dimensional and two-dimensional Green tensors for arbitrary piezoelectric quasicrystals are derived. In the piezoelectricity of quasicrystals, where phonon, phason and electric fields exist, we introduce the corresponding multifields by developing a hyperspace notation for piezoelectric quasicrystals. Using Fourier transform and the multifield formalism, the three-dimensional Green tensor for piezoelectric quasicrystals as well as its spatial gradient necessary for applications, are derived. The solutions for the “displacement”, “distortion” and “stress” multifields in the presence of a “force” multifield in a piezoelectric quasicrystal as well as the solution of the generalised Kelvin problem, are given. In addition, the two-dimensional Green tensors of piezoelectric quasicrystals as well as of quasicrystals, are determined. Full article

(This article belongs to the Special Issue Structures, Properties and Applications of Quasicrystals)

12 pages, 3037 KiB

Open AccessEditor’s ChoiceArticle

Density Functional Theory Study of Lanthanide Monoxides under High Pressure: Pressure-Induced B1–B2 Transition

by Sergio Ferrari and Daniel Errandonea

Crystals 2024, 14(10), 831; https://doi.org/10.3390/cryst14100831 - 25 Sep 2024

Cited by 3 | Viewed by 1341

Abstract

Using density functional theory, we study the influence of hydrostatic pressure on the crystal structure of lanthanide monoxides, focusing on the monoxides formed by the fifteen elements of the lanthanide series, from La to Lu. Calculations are performed using two methods for the [...] Read more.

Using density functional theory, we study the influence of hydrostatic pressure on the crystal structure of lanthanide monoxides, focusing on the monoxides formed by the fifteen elements of the lanthanide series, from La to Lu. Calculations are performed using two methods for the ambient pressure B1 (NaCl type) structure, the general gradient approximation (GGA) and the local density approximation (LDA). Through a systematic comparison with existent experimental data, we find that the first method agrees better with the experiments. In addition, considering other cubic structures previously reported for lanthanide monoxides, as B2 (CsCl type) and B3 (ZnS type), we explore the possibility of the occurrence of pressure-induced phase transitions. Based on the better accuracy of GGA to describe the B1 phase at ambient conditions, we exclusively use GGA for the high pressure study. We find, for the fifteen studied compounds, that, at ambient pressure, the B1 structure is the one with the lowest enthalpy, being therefore the most thermodynamically stable structure. We also determine that, at elevated pressures, all the studied compounds undergo a structural phase transition to the B2 phase. We finally establish the relationship between pressure and volume of the unit cell, along with the associated isothermal equation of state, determining the bulk modulus. Full article

(This article belongs to the Special Issue Pressure-Induced Phase Transformations (Third Edition))

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16 pages, 6665 KiB

Open AccessEditor’s ChoiceReview

Doped, Two-Dimensional, Semiconducting Transition Metal Dichalcogenides in Low-Concentration Regime

by Mallesh Baithi and Dinh Loc Duong

Crystals 2024, 14(10), 832; https://doi.org/10.3390/cryst14100832 - 25 Sep 2024

Cited by 4 | Viewed by 3081

Abstract

Doping semiconductors is crucial for controlling their carrier concentration and enabling their application in devices such as diodes and transistors. Furthermore, incorporating magnetic dopants can induce magnetic properties in semiconductors, paving the way for spintronic devices without an external magnetic field. This review [...] Read more.

Doping semiconductors is crucial for controlling their carrier concentration and enabling their application in devices such as diodes and transistors. Furthermore, incorporating magnetic dopants can induce magnetic properties in semiconductors, paving the way for spintronic devices without an external magnetic field. This review highlights recent advances in growing doped, two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors through various methods, like chemical vapor deposition, molecular beam epitaxy, chemical vapor transport, and flux methods. It also discusses approaches for achieving n- and p-type doping in 2D TMDC semiconductors. Notably, recent progress in doping 2D TMDC semiconductors to induce ferromagnetism and the development of quantum emitters is covered. Experimental techniques for achieving uniform doping in chemical vapor deposition and chemical vapor transport methods are discussed, along with the challenges, opportunities, and potential solutions for growing uniformly doped 2D TMDC semiconductors. Full article

(This article belongs to the Section Crystal Engineering)

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27 pages, 6432 KiB

Open AccessEditor’s ChoiceReview

Supramolecular Arrangement and Conformational and Dynamic Properties of Chiral Smectic Liquid Crystals Obtained through Nuclear Magnetic Resonance: A Brief Review

by Valentina Domenici

Crystals 2024, 14(9), 823; https://doi.org/10.3390/cryst14090823 - 20 Sep 2024

Cited by 2 | Viewed by 1175

Abstract

Ferroelectric and antiferroelectric smectic liquid crystalline (LC) phases are still at the center of investigations and interests for both their fundamental properties and variety of technological applications. This review aims to report the main contributions based on different nuclear magnetic resonance (NMR) techniques [...] Read more.

Ferroelectric and antiferroelectric smectic liquid crystalline (LC) phases are still at the center of investigations and interests for both their fundamental properties and variety of technological applications. This review aims to report the main contributions based on different nuclear magnetic resonance (NMR) techniques to the study of chiral liquid crystalline calamitic mesogens forming smectic phases, such as the SmA, the SmC* (ferroelectric), and the SmC*_A (antiferroelectric) phases. ²H NMR and ¹³C NMR techniques and their combination were of help in clarifying the local orientational properties (i.e., the molecular and fragments’ main orientational order parameters) at the transition between the SmA and the SmC* phases, and in the particular case of de Vries liquid crystals, NMR studies gave important clues regarding the actual models describing the molecular arrangement in these two phases formed by de Vries LCs. Moreover, this review describes how the combination of ²H NMR relaxation times’ analysis, ¹H NMR relaxometry, and ¹H NMR diffusometry was successfully applied to the study of chiral smectogens forming the SmC* and SmC*_A phases, with the determination of relevant parameters describing both rotational molecular and internal motions, collective dynamics, and translational self-diffusion motions. Several cases will be reported concerning NMR investigations of chiral ferroelectric and antiferroelectric phases, underlining the great potential of combined NMR approaches to the study of supramolecular, conformational, and dynamic properties of liquid crystals. Full article

(This article belongs to the Section Liquid Crystals)

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9 pages, 4348 KiB

Open AccessEditor’s ChoiceArticle

Surface Electronic Structure of Cr Doped Bi₂Se₃ Single Crystals

by Turgut Yilmaz, Xiao Tong, Zhongwei Dai, Jerzy T. Sadowski, Genda Gu, Kenya Shimada, Sooyeon Hwang, Kim Kisslinger, Elio Vescovo and Boris Sinkovic

Crystals 2024, 14(9), 812; https://doi.org/10.3390/cryst14090812 - 14 Sep 2024

Viewed by 1688

Abstract

Here, by using angle-resolved photoemission spectroscopy, we showed that Bi_2−xCr_xSe₃ single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms [...] Read more.

Here, by using angle-resolved photoemission spectroscopy, we showed that Bi_2−xCr_xSe₃ single crystals have a distinctly well-defined band structure with a large bulk band gap and undistorted topological surface states. These spectral features are unlike their thin film forms in which a large nonmagnetic gap with a distorted band structure was reported. We further provide laser-based high resolution photoemission data which reveal a Dirac point gap even in the pristine sample. The gap becomes more pronounced with Cr doping into the bulk of Bi₂Se₃. These observations show that the Dirac point can be modified by the magnetic impurities as well as the light source. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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48 pages, 7039 KiB

Open AccessEditor’s ChoiceReview

A Review of Nanocarbon-Based Anode Materials for Lithium-Ion Batteries

by Nagaraj Nandihalli

Crystals 2024, 14(9), 800; https://doi.org/10.3390/cryst14090800 - 10 Sep 2024

Cited by 7 | Viewed by 5199

Abstract

Renewable and non-renewable energy harvesting and its storage are important components of our everyday economic processes. Lithium-ion batteries (LIBs), with their rechargeable features, high open-circuit voltage, and potential large energy capacities, are one of the ideal alternatives for addressing that endeavor. Despite their [...] Read more.

Renewable and non-renewable energy harvesting and its storage are important components of our everyday economic processes. Lithium-ion batteries (LIBs), with their rechargeable features, high open-circuit voltage, and potential large energy capacities, are one of the ideal alternatives for addressing that endeavor. Despite their widespread use, improving LIBs’ performance, such as increasing energy density demand, stability, and safety, remains a significant problem. The anode is an important component in LIBs and determines battery performance. To achieve high-performance batteries, anode subsystems must have a high capacity for ion intercalation/adsorption, high efficiency during charging and discharging operations, minimal reactivity to the electrolyte, excellent cyclability, and non-toxic operation. Group IV elements (Si, Ge, and Sn), transition-metal oxides, nitrides, sulfides, and transition-metal carbonates have all been tested as LIB anode materials. However, these materials have low rate capability due to weak conductivity, dismal cyclability, and fast capacity fading owing to large volume expansion and severe electrode collapse during the cycle operations. Contrarily, carbon nanostructures (1D, 2D, and 3D) have the potential to be employed as anode materials for LIBs due to their large buffer space and Li-ion conductivity. However, their capacity is limited. Blending these two material types to create a conductive and flexible carbon supporting nanocomposite framework as an anode material for LIBs is regarded as one of the most beneficial techniques for improving stability, conductivity, and capacity. This review begins with a quick overview of LIB operations and performance measurement indexes. It then examines the recently reported synthesis methods of carbon-based nanostructured materials and the effects of their properties on high-performance anode materials for LIBs. These include composites made of 1D, 2D, and 3D nanocarbon structures and much higher Li storage-capacity nanostructured compounds (metals, transitional metal oxides, transition-metal sulfides, and other inorganic materials). The strategies employed to improve anode performance by leveraging the intrinsic features of individual constituents and their structural designs are examined. The review concludes with a summary and an outlook for future advancements in this research field. Full article

(This article belongs to the Special Issue The Development of Advanced Materials for Electrochemical Energy Conversion and Storage)

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22 pages, 25791 KiB

Open AccessEditor’s ChoiceArticle

In Situ Synthesis and Characterization of Graphitic Carbon Nitride/Metakaolin Composite Photocatalysts Using a Commercial Kaolin

by Balázs Zsirka, Orsolya Fónagy, Veronika Vágvölgyi, Tatjána Juzsakova, Lajos Fodor and Csilla Őze

Crystals 2024, 14(9), 793; https://doi.org/10.3390/cryst14090793 - 7 Sep 2024

Viewed by 1446

Abstract

Kaolin-based graphitic carbon nitride (g-CNx) composite photocatalysts were synthesized from a urea precursor using a commercial kaolin. Structural characterization by X-ray diffraction and infrared spectroscopy (FTIR) verified the successful thermal polycondensation of g-CNx along the thermal dehydroxylation of kaolinite to metakaolin at 550 [...] Read more.

Kaolin-based graphitic carbon nitride (g-CNx) composite photocatalysts were synthesized from a urea precursor using a commercial kaolin. Structural characterization by X-ray diffraction and infrared spectroscopy (FTIR) verified the successful thermal polycondensation of g-CNx along the thermal dehydroxylation of kaolinite to metakaolin at 550 °C. The g-CNx content of the composites were estimated by thermogravimetry and CHN analysis, ranging from ca. 87 m/m% to ca. 2 m/m% of dry mass. The addition of kaolin during the composite synthesis was found to have a significant effect: the yield of in situ formed g-CNx drastically decreased (from ca. 4.9 m/m% to 3.8–0.1 m/m%) with increasing kaolin content. CHN and FTIR indicated the presence of nitrogen-rich g-CNx, having a specific surface area of 50 m²/g, which synergistically increased after composite synthesis to 67–82 m²/g. Estimated optical band gaps indicated the affinity to absorb in the visible light spectrum (λ < 413 nm). Photocatalytic activity upon both UV and artificial sunlight irradiation was observed by hydroxyl radical evolution, however, without the synergistic effect expected from the favorable porosity. Full article

(This article belongs to the Section Hybrid and Composite Crystalline Materials)

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13 pages, 5828 KiB

Open AccessEditor’s ChoiceArticle

Influence of the Acetylene Flow Rate and Process Pressure on the Carbon Deposition Behavior by Thermal Chemical Vapor Deposition Process

by Gi-Hoon Kwon, Byoungho Choi, Young-Kook Lee and Kyoungil Moon

Crystals 2024, 14(9), 782; https://doi.org/10.3390/cryst14090782 - 31 Aug 2024

Cited by 1 | Viewed by 1858

Abstract

We used the chemical vapor deposition process to deposit carbon film at a high temperature (900 °C). The carbon films were deposited on AISI 1006 foils using an acetylene gas. We analyzed the carbon film deposited on the surface using Raman spectroscopy, scanning [...] Read more.

We used the chemical vapor deposition process to deposit carbon film at a high temperature (900 °C). The carbon films were deposited on AISI 1006 foils using an acetylene gas. We analyzed the carbon film deposited on the surface using Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy to define changes in the bonding structure of the carbon film. The results of Raman spectroscopy and high-resolution transmission electron microscopy revealed that as the acetylene flow rate increased, the shape of the deposited carbon film changed from graphene to graphite. In addition, in order to compare the quality of the carbon film in terms of mechanical and electrical properties, carbon films treated under various conditions were closely analyzed using nano-indenter and a sheet resistance meter. Therefore, the optimal condition (1 Torr-50 sccm) was selected in which graphene was uniformly deposited and had the lowest electrical resistance (500 Ω/sq) and highest hardness (12 GPa). Full article

(This article belongs to the Section Crystal Engineering)

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13 pages, 6423 KiB

Open AccessEditor’s ChoiceArticle

A Cost-Effective Strategy to Modify the Electrical Properties of PEDOT:PSS via Femtosecond Laser Irradiation

by Chi Zhang, Jiayue Zhou, Rui Han, Cheng Chen, Han Jiang, Xiaopeng Li, Yong Peng, Dasen Wang and Kehong Wang

Crystals 2024, 14(9), 775; https://doi.org/10.3390/cryst14090775 - 30 Aug 2024

Cited by 1 | Viewed by 1357

Abstract

Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is a commonly used conductive polymer in organic optoelectronic devices. The conductivity and work function of the PEDOT:PSS are two important parameters that significantly determine the performance of the associated optoelectronic device. Traditionally, some solvents were doped in PEDOT:PSS solution or [...] Read more.

Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is a commonly used conductive polymer in organic optoelectronic devices. The conductivity and work function of the PEDOT:PSS are two important parameters that significantly determine the performance of the associated optoelectronic device. Traditionally, some solvents were doped in PEDOT:PSS solution or soaked in PEDOT:PSS film to improve its electrical conductivity, but they damaged the integrity of PEDOT:PSS and reduce the film’s work function. Herein, for the first time, we use femtosecond laser irradiation to modify the electrical conductivity and work function of PEDOT:PSS film. We proposed that the femtosecond laser irradiation could selectively remove the superficial insulative PSS, thereby improving the electrical conductivity of the film. The femtosecond laser-irradiated PEDOT:PSS film was further employed as a hole injection layer within cutting-edge perovskite light-emitting diodes (PeLEDs). A maximum luminosity of 950 cd/m² was obtained in PeLEDs irradiated by femtosecond laser light in thin films, which is five times higher than that of the controlled device. Moreover, the external quantum efficiency of the devices was also increased from 4.6% to 6.3%. This work paved a cost-effective way to regulate the electrical properties of the PEDOT:PSS film. Full article

(This article belongs to the Section Organic Crystalline Materials)

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15 pages, 9936 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effect of Methylxanthines on Urate Crystallization: In Vitro Models of Gout and Renal Calculi

by Jaume Dietrich, Felix Grases and Antonia Costa-Bauza

Crystals 2024, 14(9), 768; https://doi.org/10.3390/cryst14090768 - 29 Aug 2024

Cited by 2 | Viewed by 1645

Abstract

Background: Common forms of pathological crystals are uric acid or urates, which are responsible for gout, urolithiasis, and other conditions. Methods: We used a kinetic–turbidimetric crystallization assay to evaluate the effect of ten specific methylxanthines on the crystallization of monosodium urate, potassium urate, [...] Read more.

Background: Common forms of pathological crystals are uric acid or urates, which are responsible for gout, urolithiasis, and other conditions. Methods: We used a kinetic–turbidimetric crystallization assay to evaluate the effect of ten specific methylxanthines on the crystallization of monosodium urate, potassium urate, and ammonium urate in conditions that mimicked urine. We also studied the effect of different levels of 7-methylxanthine in the presence of other biological compounds (albumin and hyaluronic acid) on the solubility of monosodium urate in conditions that mimicked synovial fluid. Results: The results showed that 7-methylxanthine in the range of 16.61–49.84 mg/L inhibited the crystallization of each urate when the initial urate concentration was 3 × 10⁻³ M (500 mg/L) and the conditions mimicked urine, and that the greatest inhibitory effect was for monosodium urate. In addition, 7-methylxanthine at a concentration of 25 mg/L totally prevented the crystallization of monosodium urate at an initial urate concentration of 2.38 × 10⁻³ M (400 mg/L) in conditions that mimicked synovial fluid. Moreover, at a low concentration of 7-methylxanthine, albumin and hyaluronic acid increased this inhibitory effect. Conclusions: Our in vitro results demonstrate that 7-methylxanthine inhibits the crystallization of urates in conditions that mimic synovial fluid and urine. Full article

(This article belongs to the Special Issue Pathological Biomineralization: Recent Advances and Perspectives)

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13 pages, 5500 KiB

Open AccessEditor’s ChoiceArticle

Predicting X-ray Diffraction Quality of Protein Crystals Using a Deep-Learning Method

by Yujian Shen, Zhongjie Zhu, Qingjie Xiao, Kanglei Ye, Qisheng Wang, Yue Wang and Bo Sun

Crystals 2024, 14(9), 771; https://doi.org/10.3390/cryst14090771 - 29 Aug 2024

Viewed by 1923

Abstract

Over the past few decades, significant advancements in protein crystallography have led to a steady increase in the number of determined protein structures. The X-ray diffraction experiment remains one of the primary methods for investigating protein crystal structures. To obtain information about crystal [...] Read more.

Over the past few decades, significant advancements in protein crystallography have led to a steady increase in the number of determined protein structures. The X-ray diffraction experiment remains one of the primary methods for investigating protein crystal structures. To obtain information about crystal structures, a sufficient number of high-quality crystals are typically required. At present, X-ray diffraction experiments on protein crystals primarily rely on manual selection by experimenters. However, each experiment is not only costly but also time-consuming. To address the urgent need for automatic selection of the proper protein crystal candidates for X-ray diffraction experiments, a protein-crystal-quality classification network, leveraging the ConvNeXt network architecture, is proposed. Subsequently, a new database is created, which includes protein crystal images and their corresponding X-ray diffraction images. Additionally, a novel method for categorizing protein quality based on the number of diffraction spots and the resolution is introduced. To further enhance the network’s focus on essential features of protein crystal images, a CBAM (Convolutional Block Attention Module) attention mechanism is incorporated between convolution layers. The experimental results demonstrate that the network achieves significant improvement in performing the prediction task, thereby effectively enhancing the probability of high-quality crystals being selected by experimenters. Full article

(This article belongs to the Special Issue Protein Crystallography: The State of the Art)

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30 pages, 33889 KiB

Open AccessEditor’s ChoiceReview

A Review of Additively Manufactured Iron-Based Shape Memory Alloys

by Qian Sun, Xiaojun Tan, Mingjun Ding, Bo Cao and Takeshi Iwamoto

Crystals 2024, 14(9), 773; https://doi.org/10.3390/cryst14090773 - 29 Aug 2024

Cited by 4 | Viewed by 3355

Abstract

Iron-based shape memory alloys (Fe-SMAs), traditionally manufactured, are favored in engineering applications owing to their cost-effectiveness and ease of fabrication. However, the conventional manufacturing process of Fe-SMAs is time-consuming and raw-material-wasting. In contrast, additive manufacturing (AM) technology offers a streamlined approach to the [...] Read more.

Iron-based shape memory alloys (Fe-SMAs), traditionally manufactured, are favored in engineering applications owing to their cost-effectiveness and ease of fabrication. However, the conventional manufacturing process of Fe-SMAs is time-consuming and raw-material-wasting. In contrast, additive manufacturing (AM) technology offers a streamlined approach to the integral molding of materials, significantly reducing raw material usage and fabrication time. Despite its potential, research on AMed Fe-SMAs remains in its early stages. This review provides updated information on current AM technologies utilized for Fe-SMAs and their applications. It provides an in-depth discussion on how printing parameters, defects, and post-printing microstructure control affect the mechanical properties and shape memory effect (SME) of AMed Fe-SMAs. Furthermore, this review identifies existing challenges in the AMed Fe-SMA approach and proposes future research directions, highlighting potential areas for development. The insights presented aim to guide improvements in the material properties of AMed Fe-SMAs by optimizing printing parameters and enhancing the SME through microstructure adjustment. Full article

(This article belongs to the Special Issue Shape Memory Alloys: Recent Advances and Future Perspectives)

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13 pages, 3083 KiB

Open AccessEditor’s ChoiceArticle

Effect of Lattice Misfit on the Stability of the Misfit Layer Compound (SnS)_1+xNbS₂

by Changming Fang

Crystals 2024, 14(9), 756; https://doi.org/10.3390/cryst14090756 - 26 Aug 2024

Cited by 1 | Viewed by 1288

Abstract

The prototype misfit layer compound (SnS)_1.17NbS₂ consists alternatingly of a metallic triatomic NbS₂ layer, in which Nb atoms are sandwiched by S atoms, and an insulating SnS double layer featuring a NaCl-type structure. Here we investigate the effect of [...] Read more.

The prototype misfit layer compound (SnS)_1.17NbS₂ consists alternatingly of a metallic triatomic NbS₂ layer, in which Nb atoms are sandwiched by S atoms, and an insulating SnS double layer featuring a NaCl-type structure. Here we investigate the effect of lattice misfit on the stability and chemical bonding in the misfit layer compound using a first-principles density functional theory approach. The calculations show that for the (SnS)_1+xNbS₂ approximants, the most stable one has x = 0.167, close to the experimental observations. Charge analysis finds a moderate charge transfer from SnS to NbS₂. Sn or S vacancies in the SnS part affect the electronic properties and interlayer interactions. The obtained information here helps in understanding the mechanism of formation and stability of misfit layer compounds and ferecrystals and further contributes to the design of novel multilayer compounds and emerging van der Waals heterostructures. Full article

(This article belongs to the Special Issue Microstructure and Properties of Intermetallic Compounds)

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18 pages, 4999 KiB

Open AccessEditor’s ChoiceArticle

Screening, Growing, and Validation by Catalog: Using Synthetic Intermediates from Natural Product Libraries to Discover Fragments for an Aspartic Protease Through Crystallography

by Franziska U. Huschmann, Janis Mueller, Alexander Metz, Moritz Ruf, Johanna Senst, Serghei Glinca, Johannes Schiebel, Andreas Heine and Gerhard Klebe

Crystals 2024, 14(9), 755; https://doi.org/10.3390/cryst14090755 - 25 Aug 2024

Viewed by 1437

Abstract

Fragment screening directly on protein crystals has been applied using AnalytiCon’s collection of intermediates that have been utilized to generate libraries of larger synthetic natural product-like molecules. The fragments with well-balanced physicochemical properties show an impressively high hit rate for a screen using [...] Read more.

Fragment screening directly on protein crystals has been applied using AnalytiCon’s collection of intermediates that have been utilized to generate libraries of larger synthetic natural product-like molecules. The fragments with well-balanced physicochemical properties show an impressively high hit rate for a screen using the aspartic protease endothiapepsin. The subsequent validation and expansion of the discovered fragment hits benefits from AnalytiCon’s comprehensive library design. Since the screened fragments are intermediates that share a common core with larger and closely related analogs with modulated substitution patterns, they allow for the retrieval of off-the-shelf follow-up compounds, which enable the development of design strategies for fragment optimization. A promising bicyclic core scaffold found in several fragment hits could be validated by selecting a set of enlarged follow-up compounds. Due to unexpected changes in binding mode and no significant improvement in ligand efficiency, this series was quickly deemed unsuitable and therefore discontinued. The structures of follow-up compounds of two other fragments helped to evaluate a putative fusion of two overlapping fragment hits. A design concept on how to fuse the two fragments could be proposed and helps to plan a suitable substitution pattern and promising central bridging element. Full article

(This article belongs to the Special Issue Structural Studies in Drug Discovery and Development: From the Lead to the Pharmaceutical Form)

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14 pages, 2477 KiB

Open AccessEditor’s ChoiceArticle

Technology and Dielectric Properties of BLT4 Ceramics Modified with Special Glass

by Beata Wodecka-Dus, Jolanta Makowska, Tomasz Pikula, Rafał Panek, Małgorzata Adamczyk-Habrajska and Katarzyna Osińska

Crystals 2024, 14(8), 739; https://doi.org/10.3390/cryst14080739 - 20 Aug 2024

Cited by 1 | Viewed by 1035

Abstract

Lead-boron special glass was doped into Ba_0.996La_0.004Ti_0.999O₃ (BLT4) ceramics in order to control the sintering process and grain growth, consequently obtaining materials with a well-developed microstructure. Changes in the microstructure resulted in a significant decrease in [...] Read more.

Lead-boron special glass was doped into Ba_0.996La_0.004Ti_0.999O₃ (BLT4) ceramics in order to control the sintering process and grain growth, consequently obtaining materials with a well-developed microstructure. Changes in the microstructure resulted in a significant decrease in electrical permittivity along with a substantial increase in its frequency dispersion. Glass-doped ceramics, similar to pure BLT4, are characterized by a first-order phase transition from the ferroelectric phase to the paraelectric phase. The temperature of this transition shifts slightly towards higher values with the increase in glass dopant concentration. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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14 pages, 4227 KiB

Open AccessEditor’s ChoiceArticle

Boosted Electrochemical Activity with SnO₂ Nanostructures Anchored on α-Fe₂O₃ for Improved Charge Transfer and Current Density

by Itheereddi Neelakanta Reddy, Bhargav Akkinepally, Jaesool Shim and Cheolho Bai

Crystals 2024, 14(8), 734; https://doi.org/10.3390/cryst14080734 - 18 Aug 2024

Cited by 1 | Viewed by 1275

Abstract

This study presents a straightforward and cost-effective method to enhance the photoelectrochemical (PEC) water-splitting performance of α-Fe₂O₃ (F), SnO₂ (S), and α-Fe₂O₃ decorated with SnO₂ quantum dots (FS) photoanodes in a NaOH electrolyte. The FS [...] Read more.

This study presents a straightforward and cost-effective method to enhance the photoelectrochemical (PEC) water-splitting performance of α-Fe₂O₃ (F), SnO₂ (S), and α-Fe₂O₃ decorated with SnO₂ quantum dots (FS) photoanodes in a NaOH electrolyte. The FS electrode demonstrated a notable improvement in PEC efficiency within the electrolyte. In particular, the generated charges of the FS anode in the NaOH electrolyte reached approximately 12.01 mA cm⁻² under illumination, indicating that the developed heterostructures effectively enhanced kinetics, leading to improved separation of induced carrier pairs. This active carrier-pair separation mechanism contributed considerably to the increased PEC activity in the 0.1 M NaOH electrolyte. The reduction in the bandgap of FS increased its absorption capability in visible light, which further enhanced the current density. Furthermore, the reduction in electrolyte resistance (9.71 Ω), internal resistance (20.19 Ω), charge transfer resistance (3.21 kΩ), Tafel slope (45.5 mV dec-1), limiting current density (−2.09 mA cm⁻²), and exchange current density (−3.68 mA cm⁻²) under illumination at the interface enhanced the charge density of FS. Further, a strong interaction among photoanode nanostructures significantly enhances PEC activity by improving efficient charge separation and transport, reducing recombination rates, and enabling quicker movement of charge carriers to the electrode/electrolyte interface. Thus, this study provides an effective approach to increasing the PEC activity of heterostructures. Full article

(This article belongs to the Special Issue Hybrid Materials for Energy Storage and Conversion)

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12 pages, 5019 KiB

Open AccessEditor’s ChoiceArticle

High-Quality Single-Step Growth of GaAs on C-Plane Sapphire by Molecular Beam

by Emmanuel Wangila, Calbi Gunder, Mohammad Zamani-Alavijeh, Fernando Maia de Oliveira, Serhii Kryvyi, Aida Sheibani, Yuriy I. Mazur, Shui-Qing Yu and Gregory J. Salamo

Crystals 2024, 14(8), 724; https://doi.org/10.3390/cryst14080724 - 14 Aug 2024

Cited by 1 | Viewed by 1808

Abstract

We report on the growth of high-quality GaAs semiconductor materials on an AlAs/sapphire substrate by molecular beam epitaxy. The growth of GaAs on sapphire centers on a new single-step growth technique that produces higher-quality material than a previously reported multi-step growth method. Omega-2theta [...] Read more.

We report on the growth of high-quality GaAs semiconductor materials on an AlAs/sapphire substrate by molecular beam epitaxy. The growth of GaAs on sapphire centers on a new single-step growth technique that produces higher-quality material than a previously reported multi-step growth method. Omega-2theta scans confirmed the GaAs (111) orientation. Samples grown at 700 °C displayed the highest crystal quality with minimal defects and strain, evidenced by narrow FWHM values of the rocking curve. By varying the As/Ga flux ratio and the growth temperature, we significantly improved the quality of the GaAs layer on sapphire, as compared to that obtained in multi-step studies. Photoluminescence measurements at room temperature and 77 K further support these findings. This study underscores the critical role of the As/Ga flux ratio and growth temperature in optimizing GaAs epitaxial growth on sapphire. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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21 pages, 6986 KiB

Open AccessEditor’s ChoiceArticle

Twin Peaks: Interrogating Otolith Pairs to See Whether They Keep Their Stories Straight

by Clara Lord, Sophie Berland, Vincent Haÿ, Kadda Medjoubi and Philippe Keith

Crystals 2024, 14(8), 705; https://doi.org/10.3390/cryst14080705 - 4 Aug 2024

Cited by 1 | Viewed by 1247

Abstract

To tackle the question of the reliability of otoliths as recorders of individual life events, we compared the information enclosed in otolith pairs: the sagittae pair and the sagitta/lapillus pair. We used the synchrotron XRF scanning imaging method, which enabled the comparison of [...] Read more.

To tackle the question of the reliability of otoliths as recorders of individual life events, we compared the information enclosed in otolith pairs: the sagittae pair and the sagitta/lapillus pair. We used the synchrotron XRF scanning imaging method, which enabled the comparison of this information at both global and hyperfine scales. Using otoliths of diadromous pipefish, we compared element incorporation in each pair with a focus on (i) environment and transition between water bodies with strontium (Sr) and heavy metals, (ii) temporal information and age estimation based on sulphur (S) incorporation, and (iii) otolith growth and biomineralization processes with zinc (Zn). Results show that the global information in terms of Sr and heavy metals given by both otoliths of a pair is the same and that any otolith may be used to retrieve such global data. In terms of S-based growth increment counts, the numbers are the same between two otoliths of the same kind, but the sagitta/lapillus pairs show a significant difference. Hyperfine-scale analysis of element distribution reveals that a given otolith is under the control of specific growth mechanisms, which can lead to heterogeneous elemental incorporation. The present results lead us to consider otolith growth dynamics and biomineralization processes in the context of a fluid mosaic perspective. Full article

(This article belongs to the Section Mineralogical Crystallography and Biomineralization)

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17 pages, 3562 KiB

Open AccessEditor’s ChoiceArticle

Electrosynthesis of Co-ZIF Using Bio-Derived Solvents: Electrochemical Evaluation of Synthesised MOFs as a Binder-Free Supercapacitor Electrode in Alkaline Electrolyte

by Vijayakumar Manavalan, Brad Coward, Vesna Najdanovic-Visak and Stephen D. Worrall

Crystals 2024, 14(8), 700; https://doi.org/10.3390/cryst14080700 - 1 Aug 2024

Cited by 1 | Viewed by 1607

Abstract

Supercapacitors hold promise for energy storage due to their exceptional power density and fast charge/discharge cycles. However, their performance hinges on the electrode material. Zeolitic imidazolate frameworks (ZIFs) are attractive options due to their tailorable structure and high surface area. But traditional ZIF [...] Read more.

Supercapacitors hold promise for energy storage due to their exceptional power density and fast charge/discharge cycles. However, their performance hinges on the electrode material. Zeolitic imidazolate frameworks (ZIFs) are attractive options due to their tailorable structure and high surface area. But traditional ZIF synthesis relies on toxic solvents derived from fossil fuels, hindering their envisioned environmental benefit. This study explores using bio-derived solvents for a greener and potentially superior approach. The researchers employed anodic electrodeposition to synthesise cobalt-based ZIFs (Co-ZIFs) as supercapacitor electrode materials. Two linkers (2-methylimidazole and benzimidazole) and two bio-derived solvents (Cyrene^TM and γ-valerolactone (GVL)) were investigated. X-ray diffraction analysis revealed that bio-derived solvents enhanced the crystallinity of Co-ZIFs compared to traditional solvents. Notably, Cyrene^TM promoted better crystallinity for Co-bIM/Co-mIM structures. The Full Width at Half Maximum (FWHM) analysis suggests Cyrene^TM promotes Co-bIM/Co-mIM crystallinity (lower FWHM). Co-mIM in Cyrene^TM exhibits the best crystallinity (FWHM = 0.233) compared to other ZIF samples. Scanning electron microscopy confirmed these findings, showing larger and well-defined crystals for bio-derived solvent-synthesised ZIFs. The choice of solvent significantly impacted the final ZIF structure. While 2-methylimidazole consistently formed ZIF-67 regardless of the solvent, benzimidazole exhibited solvent-dependent behaviour. GVL yielded the highly porous Co-ZIF-12 structure, whereas DMF (N,N-dimethylformamide) and Cyrene^TM produced the less porous ZIF-9. This work reports the first-ever instance of ZIF-12 synthesis via an electrochemical method, highlighting the crucial interplay between solvent and precursor molecule in determining the final ZIF product. The synthesised binder-free Co-ZIF electrodes were evaluated for supercapacitor performance. The capacitance data revealed GVL as the most effective solvent, followed by DMF and then Cyrene^TM. This suggests GVL is the preferred choice for this reaction due to its superior performance. The ZIF-12-based electrode exhibits an impressive specific capacitance (C_sp) of 44 F g⁻¹, significantly higher than those achieved by ZIF-9-Cyrene (1.2 F g⁻¹), ZIF-9-DMF (2.5 F g⁻¹), ZIF-67-GVL (35 F g⁻¹), ZIF-67-Cyrene (6 F g⁻¹), and ZIF-67-DMF (16 F g⁻¹) at 1 A g⁻¹. This surpasses the C_sp of all other ZIFs studied, including high-performing ZIF-67(GVL). ZIF-12(GVL) maintained superior C_sp even at higher current densities, demonstrating exceptional rate capability. Among the bio-derived solvents, GVL outperformed Cyrene^TM. Notably, the Co-bIM in the GVL sample exhibited a ZIF-12-like structure, offering potential advantages due to its larger pores and potentially higher surface area compared to traditional ZIF-67 and ZIF-9 structures. This work presents a significant advancement in Co-ZIF synthesis. By utilising bio-derived solvents, it offers a more sustainable and potentially superior alternative. This paves the way for the eco-friendly production of Co-ZIFs with improved properties for supercapacitors, gas separation, catalysis, and other applications. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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15 pages, 5755 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Investigation of ReSe₂ Thin Films Obtained from Magnetron Sputtered Re and ReO_x

by Kevon Kadiwala, Luize Dipane, Eriks Dipans, Arturs Bundulis, Martins Zubkins, Andrejs Ogurcovs, Jevgenijs Gabrusenoks, Dmitry Bocharov, Edgars Butanovs and Boris Polyakov

Crystals 2024, 14(8), 690; https://doi.org/10.3390/cryst14080690 - 28 Jul 2024

Cited by 2 | Viewed by 1469

Abstract

The promise of two-dimensional (2D) rhenium diselenide (ReSe₂) in electronics and optoelectronics has sparked considerable interest in this material. However, achieving the growth of high-quality ReSe₂ thin films on a wafer scale remains a significant challenge. In this study, we [...] Read more.

The promise of two-dimensional (2D) rhenium diselenide (ReSe₂) in electronics and optoelectronics has sparked considerable interest in this material. However, achieving the growth of high-quality ReSe₂ thin films on a wafer scale remains a significant challenge. In this study, we adopted a two-step method to produce ReSe₂ thin films by combining magnetron sputtering of Re and ReO_x onto flat substrates with subsequent selenization via atmospheric pressure chemical vapor transport (CVT). After analyzing the produced films using X-ray diffraction to identify the crystalline phase in formed thin film and scanning electron microscopy (SEM) to examine surface morphology, it was determined that the suitable temperature range for the 15 min selenization process with CVT is 650 °C–750 °C. Further investigation of these optimally produced ReSe₂ thin films included atomic force microscopy (AFM), X-ray photoelectron spectroscopy, and Raman spectroscopy. The bulk electrical analysis of these films and AFM and SEM surface morphology revealed a strong reliance on the type of precursor material used for their synthesis, whereas optical measurements indicated a potential for the films in non-linear optics applications, irrespective of the precursor or temperature used. This study not only provides a new pathway for the growth of ReSe₂ films but also sheds light on the synthesis approaches of other 2D transition metal dichalcogenide materials. Full article

(This article belongs to the Special Issue Two-Dimensional Materials: Synthesis, Characterization and Device Applications)

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15 pages, 6194 KiB

Open AccessEditor’s ChoiceArticle

Analysis of the Anisotropic Cyclic Material Behavior of EN AW-1050A H24 Derived from Strain-Controlled Testing Using a Clip-On Extensometer and an Optical System

by Tim Korschinsky, Benjamin Möller, Marvin Kiel and Matthias Hecht

Crystals 2024, 14(8), 686; https://doi.org/10.3390/cryst14080686 - 27 Jul 2024

Cited by 2 | Viewed by 2333

Abstract

Due to its good conductive properties, unalloyed (pure) aluminum, such as EN AW-1050A H24, finds new fields of application in electromobility. To optimize components, the cyclic material behavior must be understood and described precisely as a foundation of a proper fatigue life estimation. [...] Read more.

Due to its good conductive properties, unalloyed (pure) aluminum, such as EN AW-1050A H24, finds new fields of application in electromobility. To optimize components, the cyclic material behavior must be understood and described precisely as a foundation of a proper fatigue life estimation. Various cyclic tests were performed to not only derive the cyclic parameters to describe the material but also to find the most suitable procedure to deal with the challenges faced during the experiments. The main point of interest is the comparison between a surface-mounted clip-on extensometer and an optical system both used for strain control in cyclic tests. For the analysis of the anisotropic behavior of EN AW-1050A H24, un-notched flat specimens were extracted from sheet metal lengthways and crossways in respect to the rolling direction. While the cyclic material behavior for specimens of both directions of extraction is characterized by cyclic softening in general, the specimens extracted crossways show a strain-amplitude-dependent cyclic softening with strong strain localization especially at the contact points of the knives of the clip-on extensometer leading to an increased quantity of invalid experiments as well as sudden fractures. In the study, it was possible to show the benefits of a contactless optical strain control system when dealing with very soft metallic materials such as EN AW-1050A H24. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Anisotropic Materials)

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29 pages, 18161 KiB

Open AccessEditor’s ChoiceReview

Liquid-Crystalline Supermolecules Inducing Layer Fluctuations: From Hierarchical to Dissipative Structures

by Atsushi Yoshizawa

Crystals 2024, 14(8), 681; https://doi.org/10.3390/cryst14080681 - 26 Jul 2024

Cited by 2 | Viewed by 2307

Abstract

Liquid crystals, which have both liquid and solid properties, inevitably exhibit fluctuations. Some frustrated liquid-crystalline phases with a hierarchical structure, such as cybotactic nematic, modulated smectic, and bicontinuous cubic phases, are fascinating fluctuation-induced phases. In addition to these equilibrium phases, a pattern formation [...] Read more.

Liquid crystals, which have both liquid and solid properties, inevitably exhibit fluctuations. Some frustrated liquid-crystalline phases with a hierarchical structure, such as cybotactic nematic, modulated smectic, and bicontinuous cubic phases, are fascinating fluctuation-induced phases. In addition to these equilibrium phases, a pattern formation that is a nonequilibrium order through fluctuation is one of the most attractive research areas in soft matter. In this review, the studies on producing these fluctuation-induced orders in liquid crystals are described. Liquid-crystalline supermolecules in which several mesogens are connected via a flexible spacer have been designed. They have not only a characteristic shape but also an intra-molecular dynamic order. The supermolecules induce the fluctuations in layer structures at a molecular level, producing from the frustrated hierarchical to dynamic dissipative structures. In addition to reviewing molecular design for the hierarchical structures, the pattern propagation in a smectic phase is discussed based on the rotation of smectic blocks through Rayleigh–Bénard convection. Full article

(This article belongs to the Special Issue Advances in Liquid Crystal Dimers and Oligomers)

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15 pages, 8549 KiB

Open AccessEditor’s ChoiceArticle

Advances in the Parameter Space Concept towards Picometer Precise Crystal Structure Refinement—A Resolution Study

by Matthias Zschornak, Christian Wagner, Melanie Nentwich, Muthu Vallinayagam and Karl F. Fischer

Crystals 2024, 14(8), 684; https://doi.org/10.3390/cryst14080684 - 26 Jul 2024

Cited by 1 | Viewed by 1392

Abstract

The Parameter Space Concept (PSC) is an alternative approach to solving and refining (partial) crystal structures from very few pre-chosen X-ray or neutron diffraction amplitudes without the use of Fourier inversion. PSC interprets those amplitudes as piecewise analytic hyper-surfaces, so-called isosurfaces, in the [...] Read more.

The Parameter Space Concept (PSC) is an alternative approach to solving and refining (partial) crystal structures from very few pre-chosen X-ray or neutron diffraction amplitudes without the use of Fourier inversion. PSC interprets those amplitudes as piecewise analytic hyper-surfaces, so-called isosurfaces, in the Parameter Space, which is spanned by the spatial coordinates of all atoms of interest. The intersections of all isosurfaces constitute the (possibly degenerate) structure solution. The present feasibility study investigates the La and Sr split position of the potential high-temperature super-conductor (La_0.5Sr_1.5)MnO₄,

I 4

/mmm, with a postulated total displacement between La and Sr of a few

p

m

by theoretical amplitudes of pre-selected

0 0 l

reflections (

l = 2, 4, \dots, 20

). The revision of 15-year-old results with state-of-the-art computing equipment enhances the former simplified model by varying the scattering power ratio

f_{\begin{matrix} La \end{matrix}} / f_{\begin{matrix} Sr \end{matrix}}

, as exploitable by means of resonant scattering contrast at synchrotron facilities, and irrevocably reveals one of the two originally proposed solutions as being a “blurred” pseudo-solution. Finally, studying the resolution limits of PSC as a function of intensity errors by means of Monte-Carlo simulations shows both that the split can only be resolved for sufficiently low errors and, particularly for the resonant scattering contrast, a theoretical precision down to

\pm 0.19

p

m

can be achieved for this specific structural problem. Full article

(This article belongs to the Section Crystal Engineering)

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15 pages, 530 KiB

Open AccessEditor’s ChoiceArticle

Directional Acoustic Bulk Waves in a 2D Phononic Crystal

by Pierre A. Deymier, Jérôme O. Vasseur, Keith Runge, Krishna Muralidharan, Alexander Khanikaev and Andrea Alù

Crystals 2024, 14(8), 674; https://doi.org/10.3390/cryst14080674 - 24 Jul 2024

Cited by 1 | Viewed by 1447

Abstract

We used the transfer matrix method to investigate the conditions supporting the existence of directional bulk waves in a two-dimensional (2D) phononic crystal. The 2D crystal was a square lattice of unit cells composed of rectangular subunits constituted of two different isotropic continuous [...] Read more.

We used the transfer matrix method to investigate the conditions supporting the existence of directional bulk waves in a two-dimensional (2D) phononic crystal. The 2D crystal was a square lattice of unit cells composed of rectangular subunits constituted of two different isotropic continuous media. We established the conditions on the geometry of the phononic crystal and its constitutive media for the emergence of waves, which, for the same handedness, exhibited a non-zero amplitude in one direction within the crystal’s 2D Brillouin zone and zero amplitude in the opposite direction. Due to time-reversal symmetry, the crystal supported propagation in the reverse direction for the opposite handedness. These features may enable robust directional propagation of bulk acoustic waves and topological acoustic technology. Full article

(This article belongs to the Special Issue Metamaterials and Their Devices)

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12 pages, 3853 KiB

Open AccessEditor’s ChoiceArticle

An Analysis of Protein Crystals Grown under Microgravity Conditions

by Keegan Jackson, Rebecca Hoff, Hannah Wright, Ashley Wilkinson, Frances Brewer, Amari Williams, Ben Whiteside, Mark R. Macbeth and Anne M. Wilson

Crystals 2024, 14(7), 652; https://doi.org/10.3390/cryst14070652 - 16 Jul 2024

Cited by 2 | Viewed by 2556

Abstract

Microgravity has been shown to be an excellent tool for protein crystal formation. A retrospective analysis of all publicly available crystallization data, including many that have not yet been published, clearly demonstrates the value of the microgravity environment for producing superior protein crystals. [...] Read more.

Microgravity has been shown to be an excellent tool for protein crystal formation. A retrospective analysis of all publicly available crystallization data, including many that have not yet been published, clearly demonstrates the value of the microgravity environment for producing superior protein crystals. The parameters in the database (the Butler Microgravity Protein Crystal Database, BμCDB) that were evaluated pertain to both crystal morphology and diffraction quality. Success metrics were determined as improvements in size, definition, uniformity, mosaicity, diffraction quality, resolution limits, and B factor. The proteins in the databases were evaluated by molecular weight, protein type, the number of subunits, space group, and Mattew’s Coefficient. Compared to ground experiments, crystals grown in a microgravity environment continue to show improvement across all metrics evaluated. General trends as well as numerical differences are included in the assessment of the BμCDB. The microgravity environment improves crystal formation across a spectrum of metrics and the datasets utilized for this investigation are excellent tools for this evaluation. Full article

(This article belongs to the Section Biomolecular Crystals)

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11 pages, 3629 KiB

Open AccessEditor’s ChoiceArticle

Thermal Behavior of Clinoptilolite

by Magdalena Król, Jakub Dechnik, Patryk Szymczak, Bartosz Handke, Magdalena Szumera and Paweł Stoch

Crystals 2024, 14(7), 646; https://doi.org/10.3390/cryst14070646 - 14 Jul 2024

Cited by 5 | Viewed by 2039

Abstract

Understanding the thermal properties of zeolites is crucial for their industrial applications. This study explores the thermal stability and dehydration process of clinoptilolite using high-temperature X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Clinoptilolite’s thermal decomposition was monitored from 25 °C to [...] Read more.

Understanding the thermal properties of zeolites is crucial for their industrial applications. This study explores the thermal stability and dehydration process of clinoptilolite using high-temperature X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Clinoptilolite’s thermal decomposition was monitored from 25 °C to 1200 °C, with results analyzed based on its crystal structure. Principal components analysis (PCA) of the DRIFT spectra indicated progressive water removal and dehydration upon heating, leading to the formation of hydrogen bonds. Thermogravimetric analysis (TGA) revealed a two-step endothermic weight loss: initially, physically adsorbed water was lost up to 100 °C, followed by the removal of tightly bound water and hydroxyl groups until 800 °C. Clinoptilolite remained the dominant phase up to 800 °C, after which albite and cristobalite took over. Rietveld refinement showed that the sample initially contained 70% clinoptilolite, 24% albite, and 6% cristobalite. Above 800 °C, clinoptilolite disappeared, leaving 93% albite and 7% cristobalite. FT-IR spectra changes due to water loss were evident: drying of adsorbed water occurred up to 75 °C and minimal changes were observed from 75 °C to 135 °C, followed by further dehydration until 240 °C. Complete dehydration was confirmed by the disappearance of OH stretching vibration bands by 395 °C, consistent with TGA findings. Full article

(This article belongs to the Section Hybrid and Composite Crystalline Materials)

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18 pages, 4122 KiB

Open AccessEditor’s ChoiceArticle

Crystallization of Calcium Carbonate and Calcium Phosphate Phases in Silica Hydrogel: Morphological and Compositional Characterization

by Nuria Sánchez-Pastor, André Jorge Pinto, Pablo del Buey Fernández and José Manuel Astilleros

Crystals 2024, 14(7), 635; https://doi.org/10.3390/cryst14070635 - 10 Jul 2024

Cited by 1 | Viewed by 2055

Abstract

The present study showcases a series of crystallization experiments using a specially designed double diffusion system to grow crystals belonging to the calcium carbonate–phosphate system. The experimental U-shaped device comprised two vertical solution containers, separated by a horizontal column of silica hydrogel. Each [...] Read more.

The present study showcases a series of crystallization experiments using a specially designed double diffusion system to grow crystals belonging to the calcium carbonate–phosphate system. The experimental U-shaped device comprised two vertical solution containers, separated by a horizontal column of silica hydrogel. Each container was filled with 0.5 M CaCl₂ and 0.5 M Na₂CO₃ solutions, which diffused through the gel column over time. Na₃PO₄ solutions, with 50 and 500 ppm concentrations, were incorporated into the gel in different experiments, resulting in a homogeneous distribution of phosphate concentrations within the diffusion column. After 15- and 30-day incubation periods post-nucleation, the crystals formed in different sections of the gel were carefully extracted and studied with scanning electron microscopy and electron microprobe. Additionally, Raman spectra were collected from the samples using a confocal Raman microscope, providing further insights into their molecular composition and structural properties. The obtained results show that under the induced experimental conditions (i) phosphate incorporates into calcite’s structure, and (ii) the growth of calcium phosphates in the presence of carbonate ions involves the sequential, heterogeneous nucleation of CO₃-bearing OCP/HAP-like phases, with Raman spectral characteristics very similar to those of bioapatites. Full article

(This article belongs to the Collection Topic Collection: Mineralogical Crystallography)

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9 pages, 2998 KiB

Open AccessEditor’s ChoiceArticle

Synthesis, Crystal Structure, and Electropolymerization of 1,4-Di([2,2′-bithiophen]-3-yl)buta-1,3-diyne

by Alessandro Pedrini, Chiara Massera, Enrico Dalcanale, Marco Giannetto and Roberta Pinalli

Crystals 2024, 14(7), 620; https://doi.org/10.3390/cryst14070620 - 5 Jul 2024

Viewed by 1534

Abstract

For their great structural versatility, thiophene-based π-conjugated systems have been widely exploited in the preparation of low band gap materials. Here, we report the synthesis of a highly conjugated tetrathiophene system, namely 1,4-di([2,2′-bithiophen]-3-yl)buta-1,3-diyne (1), that presents two bithiophene units connected at [...] Read more.

For their great structural versatility, thiophene-based π-conjugated systems have been widely exploited in the preparation of low band gap materials. Here, we report the synthesis of a highly conjugated tetrathiophene system, namely 1,4-di([2,2′-bithiophen]-3-yl)buta-1,3-diyne (1), that presents two bithiophene units connected at position 3 by a butadiynylene spacer. Single-crystal X-ray diffraction (SC-XRD) analysis elucidated the structure of 1, confirming the planarity of the molecule. The molecule was then electropolymerized onto the surface of a gold-coated piezoelectric quartz crystal, showing a high reactivity that is ascribable to the extended conjugation. The frontier molecular orbital energies of 1 were obtained via DFT optimization performed on the crystal structure-derived molecular geometry. Finally, DFT was also used to estimate the polymer band gap. Full article

(This article belongs to the Special Issue Synthesis, Characterization and Applications of Crystalline Electroconductive Polymers)

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13 pages, 8448 KiB

Open AccessEditor’s ChoiceArticle

Effect of Silver Vanadate Nanowires Addition on Structural and Morphological Properties of Dental Porcelain Prepared from Economic Raw Materials

by Badr Eddine Sakhkhane, Marieta Mureșan-Pop, Lucian Barbu-Tudoran, Tamás Lovász and Liliana Bizo

Crystals 2024, 14(7), 616; https://doi.org/10.3390/cryst14070616 - 3 Jul 2024

Cited by 1 | Viewed by 1768

Abstract

In addition to many materials, silver vanadate (AgVO₃) has gained interest due to its antimicrobial properties, which opens up the potential for use as an antibacterial agent for biomedical applications. This work aimed to study the effect of AgVO₃ addition [...] Read more.

In addition to many materials, silver vanadate (AgVO₃) has gained interest due to its antimicrobial properties, which opens up the potential for use as an antibacterial agent for biomedical applications. This work aimed to study the effect of AgVO₃ addition on the structural and morphological properties of a developed dental porcelain (DP) prepared from natural raw materials. AgVO₃ nanowires, prepared by the coprecipitation method, were added in different amounts (1, 3, and 5 wt.%) to a DP mass with the initial composition of 80 wt.% feldspar, 15 wt.% quartz, and 5 wt.% kaolin, obtained by sintering the mixture at 1300 °C. The structural and morphological properties of AgVO₃ and DP were investigated by X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), and transmission electron microscopy (TEM). The results showed the formation of α-AgVO₃ nanowires coated with semispherical metallic silver nanoparticles. Moreover, α-AgVO₃ additions do not influence the structural and morphological properties of DP, with the presence of Ag and V clearly identified in the DP with the α-AgVO₃ addition. Our findings highlight the potential of this novel material for use in various dental applications. Future studies need to establish the antibacterial properties of the prepared dental material. Full article

(This article belongs to the Special Issue Ceramics: Processes, Microstructures, and Properties)

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50 pages, 12170 KiB

Open AccessEditor’s ChoiceReview

Advancements in ZnO-Based Photocatalysts for Water Treatment: A Comprehensive Review

by Souad Abou Zeid and Yamin Leprince-Wang

Crystals 2024, 14(7), 611; https://doi.org/10.3390/cryst14070611 - 30 Jun 2024

Cited by 40 | Viewed by 6222

Abstract

Water contamination remains a pressing global concern, necessitating the development of effective and sustainable water treatment solutions. Zinc oxide (ZnO) has garnered significant attention for its potential applications in photocatalysis due to its unique properties and versatile nature. This review synthesizes recent research [...] Read more.

Water contamination remains a pressing global concern, necessitating the development of effective and sustainable water treatment solutions. Zinc oxide (ZnO) has garnered significant attention for its potential applications in photocatalysis due to its unique properties and versatile nature. This review synthesizes recent research findings on the advancement in ZnO-based photocatalysts for water treatment, encompassing synthesis methods, structure modifications for photocatalytic efficiency enhancement, toxicity assessments, and applications in diverse water treatment processes. By critically analyzing the strategies to enhance the photocatalytic performance of ZnO and its role in addressing water pollution challenges, this review provides valuable insights into the evolving landscape of ZnO-based photocatalysts for achieving efficient and environmentally friendly water treatment systems. This review emphasizes the transformative potential of ZnO-based photocatalysts in revolutionizing water treatment methodologies and underscores the importance of continued research and innovation in harnessing ZnO’s capabilities for sustainable water purification. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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12 pages, 4097 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Template Reset Operation on the Number of Crystals Precipitated at the Air–Solution Template Interface

by Bolor-Uyanga Tumurbaatar, Shuntaro Amari and Hiroshi Takiyama

Crystals 2024, 14(7), 591; https://doi.org/10.3390/cryst14070591 - 27 Jun 2024

Viewed by 1608

Abstract

The application of template crystallization to developing novel crystalline materials has attracted attention. However, when the air–solution interface becomes the template interface and the target material crystallizes, new nucleation at the template interface is prevented, which is predicted to prevent the increase in [...] Read more.

The application of template crystallization to developing novel crystalline materials has attracted attention. However, when the air–solution interface becomes the template interface and the target material crystallizes, new nucleation at the template interface is prevented, which is predicted to prevent the increase in the total number of crystals. In this study, we investigated the effect of operations that change the driving force at the air–solution template interface on the number of crystals at the interface. The number of crystals precipitated by changing the local supersaturation was investigated by a novel “template reset” operation, in which the concentration driving force near the template interface is changed by dissolving the crystals at the interface, once precipitated. The results showed that the number of crystals increased significantly after the template reset operation, and the particle size distribution was also improved. The temperature of the solution near the interface after the template reset operation was higher than that of the solution at the bottom of the petri dish and the prepared saturated solution, suggesting that the driving force of crystallization was higher. Full article

(This article belongs to the Section Industrial Crystallization)

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25 pages, 4950 KiB

Open AccessEditor’s ChoiceArticle

Double-Helical Tiled Chain Structure of the Twist-Bend Liquid Crystal Phase in CB7CB

by Michael R. Tuchband, Min Shuai, Keri A. Graber, Dong Chen, Chenhui Zhu, Leo Radzihovsky, Arthur Klittnick, Lee Foley, Alyssa Scarbrough, Jan H. Porada, Mark Moran, Joseph Yelk, Justin B. Hooper, Xiaoyu Wei, Dmitry Bedrov, Cheng Wang, Eva Korblova, David M. Walba, Alexander Hexemer, Joseph E. Maclennan, Matthew A. Glaser and Noel A. Clark Show full author list Hide full author list

Crystals 2024, 14(7), 583; https://doi.org/10.3390/cryst14070583 - 25 Jun 2024

Cited by 4 | Viewed by 1995

Abstract

The twist-bend nematic liquid crystal phase is a three-dimensional fluid in which achiral bent molecules spontaneously form an orientationally ordered, macroscopically chiral, heliconical winding of a ten nanometer-scale pitch in the absence of positional ordering. Here, the structure of the twist-bend phase of [...] Read more.

The twist-bend nematic liquid crystal phase is a three-dimensional fluid in which achiral bent molecules spontaneously form an orientationally ordered, macroscopically chiral, heliconical winding of a ten nanometer-scale pitch in the absence of positional ordering. Here, the structure of the twist-bend phase of the bent dimer CB7CB and its mixtures with 5CB is characterized, revealing a hidden invariance of the self-assembly of the twist-bend structure of CB7CB, such that over a wide range of concentrations and temperatures, the helix pitch and cone angle change as if the ground state for a pitch of the TB helix is an inextensible heliconical ribbon along the contour formed by following the local molecular long axis (the director). Remarkably, the distance along the length for a single turn of this helix is given by 2πR_mol, where R_mol is the radius of bend curvature of a single all-trans CB7CB molecule. This relationship emerges from frustrated steric packing due to the bent molecular shape: space in the fluid that is hard to fill attracts the most flexible molecular subcomponents, a theme of nanosegregation that generates self-assembled, oligomer-like correlations of interlocking bent molecules in the form of a brickwork-like tiling of pairs of molecular strands into duplex double-helical chains. At higher temperatures in the twist-bend phase, the cone angle is small, the director contour is nearly along the helix axis z, and the duplex chains are sequences of biaxial elements formed by overlapping half-molecule pairs, with an approximately 45° rotation of the biaxis between each such element along the chain. Full article

(This article belongs to the Section Liquid Crystals)

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15 pages, 3621 KiB

Open AccessEditor’s ChoiceArticle

Completing the Ba–As Compositional Space: Synthesis and Characterization of Three New Binary Zintl Arsenides, Ba₃As₄, Ba₅As₄, and Ba₁₆As₁₁

by Spencer R. Watts, Lindsey M. Wingate, Svilen Bobev and Sviatoslav Baranets

Crystals 2024, 14(6), 570; https://doi.org/10.3390/cryst14060570 - 20 Jun 2024

Cited by 1 | Viewed by 2110

Abstract

Three novel binary barium arsenides, Ba₃As₄, Ba₅As₄, and Ba₁₆As₁₁, were synthesized and their crystal and electronic structures were investigated. Structural data collected via the single-crystal X-ray diffraction method indicate that the [...] Read more.

Three novel binary barium arsenides, Ba₃As₄, Ba₅As₄, and Ba₁₆As₁₁, were synthesized and their crystal and electronic structures were investigated. Structural data collected via the single-crystal X-ray diffraction method indicate that the anionic substructures of all three novel compounds are composed of structural motifs based on the homoatomic As–As contacts, with [As₂]⁴⁻ dimers found in Ba₅As₄ and Ba₁₆As₁₁, and an [As₄]⁶⁻ tetramer found in Ba₃As₄. Ba₃As₄ and Ba₅As₄ crystallize in the orthorhombic crystal system—with the non-centrosymmetric space group Fdd2 (a = 15.3680(20) Å, b = 18.7550(30) Å, c = 6.2816(10) Å) for the former, and the centrosymmetric space group Cmce (a = 16.8820(30) Å, b = 8.5391(16) Å, and c = 8.6127(16) Å) for the latter—adopting Eu₃As₄ and Eu₅As₄ structure types, respectively. The heavily disordered Ba₁₆As₁₁ structure was solved in the tetragonal crystal system with the space group

P \bar{4} 2_{1} m

(a = 12.8944(12) Å and c = 11.8141(17) Å). The Zintl concept can be applied to each of these materials as follows: Ba₃As₄ = (Ba²⁺)₃[As₄]⁶⁻, Ba₅As₄ = (Ba²⁺)₅(As³⁻)₂[As₂]⁴⁻, and 2 × Ba₁₆As₁₁ = (Ba²⁺)₃₂(As³⁻) ≈ ₂₀[As₂]⁴⁻ ≈ 1, pointing to the charge-balanced nature of these compounds. Electronic structure calculations indicate narrow bandgap semiconducting behavior, with calculated bandgaps of 0.47 eV for Ba₃As₄, 0.34 eV for Ba₅As₄, and 0.33 eV for Ba₁₆As₁₁. Full article

(This article belongs to the Special Issue Research on Thermoelectric Materials: Waste Heat into Renewable Energy)

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21 pages, 11142 KiB

Open AccessEditor’s ChoiceReview

Recent Progress of Floating-Zone Techniques for Bulk Single-Crystal Growth

by Naoki Kikugawa

Crystals 2024, 14(6), 552; https://doi.org/10.3390/cryst14060552 - 14 Jun 2024

Cited by 4 | Viewed by 3663

Abstract

This review describes the recent progress of floating-zone techniques for bulk single-crystal growth. The most crucial point of the crucible-free technique is to keep the molten zone stable. It has been investigated and reported to yield a steeper temperature gradient at the liquid–solid [...] Read more.

This review describes the recent progress of floating-zone techniques for bulk single-crystal growth. The most crucial point of the crucible-free technique is to keep the molten zone stable. It has been investigated and reported to yield a steeper temperature gradient at the liquid–solid interface along the growth direction and a homogeneous molten liquid along the rotation axis. This article overviews several recent achievements starting from the conventional setup, particularly for lamps equipped in horizontal or vertical configurations, tilting mirrors, shielding the irradiation, and filament sizes for the optical-lamp floating-zone furnaces. Also, the recently advancing laser-heated floating-zone furnaces are described. Throughout the article, the author emphasizes that the floating-zone technique has been a powerful tool for crystal growth since the 1950s with its roots in the zone-melting method, and it has still been advancing for further materials’ growth such as quantum materials with modern scientific concepts. Full article

(This article belongs to the Special Issue Advances in Crystal Growth: Pioneering Materials for Tomorrow's Technologies)

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17 pages, 7761 KiB

Open AccessEditor’s ChoiceArticle

Evaluating the Effect of Hydrogen on the Tensile Properties of Cold-Finished Mild Steel

by Emmanuel Sey and Zoheir N. Farhat

Crystals 2024, 14(6), 529; https://doi.org/10.3390/cryst14060529 - 31 May 2024

Cited by 3 | Viewed by 1580

Abstract

One of the major sources of catastrophic failures and deterioration of the mechanical properties of metals, such as ductility, toughness, and strength, in various engineering components during application is hydrogen embrittlement (HE). It occurs as a result of the adsorption, diffusion, and interaction [...] Read more.

One of the major sources of catastrophic failures and deterioration of the mechanical properties of metals, such as ductility, toughness, and strength, in various engineering components during application is hydrogen embrittlement (HE). It occurs as a result of the adsorption, diffusion, and interaction of hydrogen with various metal defects like dislocations, voids, grain boundaries, and oxide/matrix interfaces due to its small atomic size. Over the years, extensive effort has been dedicated to understanding hydrogen embrittlement sources, effects, and mechanisms. This study aimed at assessing the tensile properties, toughness, ductility, and susceptibility to hydrogen embrittlement of cold-finished mild steel. Steel coupons were subjected to electrochemical hydrogen charging in a carefully chosen alkaline solution over a particular time and at various charging current densities. Tensile property tests were conducted immediately after the charging process, and the results were compared with those of uncharged steel. The findings revealed a clear drop in toughness and ductility with increasing hydrogen content. Fracture surfaces were examined to determine the failure mechanisms. This evaluation has enabled the prediction of steel’s ability to withstand environments with elevated hydrogen concentrations during practical applications. Full article

(This article belongs to the Special Issue Hydrogen Embrittlement of Metals)

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11 pages, 5467 KiB

Open AccessEditor’s ChoiceArticle

Tailoring the Magnetic and Hyperthermic Properties of Biphase Iron Oxide Nanocubes through Post-Annealing

by Supun B. Attanayake, Amit Chanda, Raja Das, Manh-Huong Phan and Hariharan Srikanth

Crystals 2024, 14(6), 519; https://doi.org/10.3390/cryst14060519 - 30 May 2024

Cited by 1 | Viewed by 1262

Abstract

Tailoring the magnetic properties of iron oxide nanosystems is essential to expanding their biomedical applications. In this study, 34 nm iron oxide nanocubes with two phases consisting of Fe₃O₄ and α-Fe₂O₃ were annealed for 2 h in [...] Read more.

Tailoring the magnetic properties of iron oxide nanosystems is essential to expanding their biomedical applications. In this study, 34 nm iron oxide nanocubes with two phases consisting of Fe₃O₄ and α-Fe₂O₃ were annealed for 2 h in the presence of O₂, N₂, He, and Ar to tune the respective phase volume fractions and control their magnetic properties. X-ray diffraction and magnetic measurements were carried out post-treatment to evaluate changes in the treated samples compared to the as-prepared samples, showing an enhancement of the α-Fe₂O₃ phase in the samples annealed with O₂ while the others indicated a Fe₃O₄ enhancement. Furthermore, the latter samples indicated enhancements in crystallinity and saturation magnetization, while coercivity enhancements were the most significant in samples annealed with O₂, resulting in the highest specific absorption rates (of up to 1000 W/g) in all the applied fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia measurements. The general enhancement of the specific absorption rate post-annealing underscores the importance of the annealing atmosphere in the enhancement of the magnetic and structural properties of nanostructures. Full article

(This article belongs to the Section Hybrid and Composite Crystalline Materials)

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23 pages, 12447 KiB

Open AccessEditor’s ChoiceArticle

Novel Salts of Heterocyclic Polyamines and 5-Sulfosalicylic Acid: Synthesis, Crystal Structure, and Hierarchical Supramolecular Interactions

by Joanna Bojarska, Krzysztof Łyczko and Adam Mieczkowski

Crystals 2024, 14(6), 497; https://doi.org/10.3390/cryst14060497 - 24 May 2024

Cited by 3 | Viewed by 1628

Abstract

A series of novel salts of heterocyclic polyamines with 5-sulfosalicylic acid (C₄H₇N₄⁺)(C₇H₅O₆S⁻)∙2(H₂O) (1), (C₄H₆ClN₄⁺)(C₇H₅ [...] Read more.

A series of novel salts of heterocyclic polyamines with 5-sulfosalicylic acid (C₄H₇N₄⁺)(C₇H₅O₆S⁻)∙2(H₂O) (1), (C₄H₆ClN₄⁺)(C₇H₅O₆S⁻)∙H₂O (2), (C₅H₈N₃⁺)(C₇H₅O₆S⁻)∙H₂O (3), (C₅H₇N₆⁺)(C₇H₅O₆S⁻)∙H₂O (4), (C₆H₁₄N₂²⁺)(C₇H₄O₆S²⁻)∙H₂O (5), and (C₁₄H₁₉N₂⁺)(C₇H₅O₆S⁻) (6) have been successfully synthesized. Their crystal structures have been determined by single-crystal X-ray diffraction. Overall, compounds adopt a layered structure with aminium cations and 5-sulfosalicylic anions linked via water molecules. The solid-state architectures of these compounds are dominated by O(N,H)-H⋯O and N-H⋯N hydrogen bonds and stabilized by weak interconnects. C-Cl⋯π and S-O⋯π interactions, apart from π⋯π and C-H(O)⋯π, were reported. Diverse approaches were used to study the effect of substituents in the polyamines in solid-state arrangement. A Hirshfeld surface analysis, with associated 3D Hirshfeld surface maps and 2D fingerprint plots, molecular electrostatic potential, and energy frameworks were used to comprehensively investigate the nature and hierarchy of non-covalent interactions and inspect supramolecular differences. The contact enrichment ratio calculations provided deeper insight into the propensity of interconnects to influence crystal packing. The evaluation of the effects of H-bonding synthons resulting from different substituents in the polyamines on self-assemblies is also presented. In the context of crystal engineering, a specific intramolecular synthon via O-H⋯O observed in nearly all crystals can be employed in the pseudo-cyclic replacement strategy in the design of new molecules. Full article

(This article belongs to the Special Issue Heterocyclic Organic Compounds: Crystal Structure and Their Properties)

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15 pages, 2466 KiB

Open AccessEditor’s ChoiceArticle

Space Group Choice for an Octahedral Zn Complex with Nalidixic Acid and (R,R)-Diaminocyclohexane as Ligands: Get the Stereochemistry Right

by Martin Lutz and Tom W. Müller

Crystals 2024, 14(6), 498; https://doi.org/10.3390/cryst14060498 - 24 May 2024

Cited by 1 | Viewed by 1562

Abstract

With this report, the space group of

[Z n (N a l) {(D A C H)}_{2}] C l

is corrected (

N a l

: nalidixic acid mono-anion;

D A C H

: diaminocyclohexane) from its [...] Read more.

With this report, the space group of

[Z n (N a l) {(D A C H)}_{2}] C l

is corrected (

N a l

: nalidixic acid mono-anion;

D A C H

: diaminocyclohexane) from its wrong description in the literature. In the correct, non-centrosymmetric space group

P 1

, the crystal structure is well ordered and the stereochemistry is correct. Crystallographic tools to recognize the correct symmetry are described. This work encourages experienced and inexperienced scientists to remain critical about the output of automatic, black-box crystallographic software. Full article

(This article belongs to the Section Organic Crystalline Materials)

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13 pages, 752 KiB

Open AccessEditor’s ChoiceReview

Machine Learning Methods to Improve Crystallization through the Prediction of Solute–Solvent Interactions

by Aatish Kandaswamy and Sebastian P. Schwaminger

Crystals 2024, 14(6), 501; https://doi.org/10.3390/cryst14060501 - 24 May 2024

Cited by 2 | Viewed by 2498

Abstract

Crystallization plays a crucial role in defining the quality and functionality of products across various industries, including pharmaceutical, food and beverage, and chemical manufacturing. The process’s efficiency and outcome are significantly influenced by solute–solvent interactions, which determine the crystalline product’s purity, size, and [...] Read more.

Crystallization plays a crucial role in defining the quality and functionality of products across various industries, including pharmaceutical, food and beverage, and chemical manufacturing. The process’s efficiency and outcome are significantly influenced by solute–solvent interactions, which determine the crystalline product’s purity, size, and morphology. These attributes, in turn, impact the product’s efficacy, safety, and consumer acceptance. Traditional methods of optimizing crystallization conditions are often empirical, time-consuming, and less adaptable to complex chemical systems. This research addresses these challenges by leveraging machine learning techniques to predict and optimize solute–solvent interactions, thereby enhancing crystallization outcomes. This review provides a novel approach to understanding and controlling crystallization processes by integrating supervised, unsupervised, and reinforcement learning models. Machine learning not only improves product the quality and manufacturing efficiency but also contributes to more sustainable industrial practices by minimizing waste and energy consumption. Full article

(This article belongs to the Section Biomolecular Crystals)

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12 pages, 3858 KiB

Open AccessEditor’s ChoiceArticle

Wide Temperature Stability of BaTiO₃-NaNbO₃-Gd₂O₃ Dielectric Ceramics with Grain Core–Shell Structure

by Zicheng Zhao, Yaoning Bai, Mingwei Li and Huiming Ji

Crystals 2024, 14(6), 488; https://doi.org/10.3390/cryst14060488 - 23 May 2024

Cited by 2 | Viewed by 1473

Abstract

As consumer electronics and industrial control systems continue to evolve, the operating temperature range of capacitors is gradually increasing. Barium titanate-based ceramic capacitors are widely used in the field of high dielectrics, so temperature-stable barium titanate-based dielectric materials have been a hot research [...] Read more.

As consumer electronics and industrial control systems continue to evolve, the operating temperature range of capacitors is gradually increasing. Barium titanate-based ceramic capacitors are widely used in the field of high dielectrics, so temperature-stable barium titanate-based dielectric materials have been a hot research topic in the field of dielectric ceramics. The construction of a core–shell structure by unequal doping is an effective way to obtain temperature-stable dielectric materials. At the same time, this structure retains part of the highly dielectric tetragonal phase, and materials with overall high dielectric constants can be obtained. In this work, we prepared BaTiO₃-xNaNbO₃-0.002Gd₂O₃ (x = 1.0–6.0 mol%) as well as BaTiO₃-0.05NaNbO₃-yGd₂O₃ (y = 0–0.30 mol%) dielectric ceramics. On the basis of high-electronic-bandgap NaNbO₃-modified BaTiO₃ dielectric ceramics, a core–shell structure with a larger proportion of core phase was obtained by further doping the amphiphilic rare-earth oxide Gd₂O₃. By designing this core–shell structure, the temperature stability range of capacitors can be expanded. At a doping level of 5.0 mol% NaNbO₃ and 0.20 mol% Gd₂O₃, the room temperature dielectric constant ε_r = 4266 and dielectric loss tan δ = 0.95% conforms to the X8R standard (from −55 °C to 150 °C, TCC < ±15%); volume resistivity ρ_v = 10,200 GΩ·cm and breakdown strength E_b = 13.5 kV/mm is attained in BaTiO₃-based ceramics. The system has excellent dielectric and insulating properties; it provides a new solution for temperature-stable dielectric ceramics. Full article

(This article belongs to the Special Issue Advanced Ferroelectric, Piezoelectric and Dielectric Ceramics)

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19 pages, 3206 KiB

Open AccessEditor’s ChoiceArticle

Novel Quaternary Ammonium Aldimine Derivatives Featuring 3,4,5-Trimethoxy Phenyl Fragment: Synthesis, Crystal Structure and Evaluation of Antioxidant and Antibacterial Activity

by Rusi Rusew, Mariya Georgieva, Vanya Kurteva and Boris Shivachev

Crystals 2024, 14(6), 486; https://doi.org/10.3390/cryst14060486 - 22 May 2024

Viewed by 1557

Abstract

This study demonstrates the synthesis of five novel quaternary ammonium aldimines through a two-step synthetic route involving a condensation reaction between 4-pyridincarboxyaldehyde and 3,4,5-trimethoxyaniline, followed by the quaternization of the pyridine N-atom with various aromatic α-bromo ketones. The newly obtained compounds underwent characterization [...] Read more.

This study demonstrates the synthesis of five novel quaternary ammonium aldimines through a two-step synthetic route involving a condensation reaction between 4-pyridincarboxyaldehyde and 3,4,5-trimethoxyaniline, followed by the quaternization of the pyridine N-atom with various aromatic α-bromo ketones. The newly obtained compounds underwent characterization for both purity and molecular structure, utilizing HR-MS, 1D, and 2D NMR spectroscopy in solution, as well as a comparison between single-crystal and powder X-ray analyses in a solid state. The thermal behavior of the studied compounds was evaluated using differential scanning calorimetry (DSC). The antioxidant properties of the compounds were assessed through DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging and ferric-reducing antioxidant power (FRAP) assays, employing Trolox as a standard. The performed in vitro antibacterial screening indicates a selective antibacterial activity against Gram-negative K. pneumoniae and P. aeruginosa, while no such activity is detected for Gram-negative E. coli and Gram-positive S. aureus. Full article

(This article belongs to the Special Issue Protein Crystallography: The State of the Art)

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28 pages, 12894 KiB

Open AccessEditor’s ChoiceReview

Crystal Morphology Prediction Models and Regulating Methods

by Yuan Gao, Wenxi Song, Jinyue Yang, Xiongtao Ji, Na Wang, Xin Huang, Ting Wang and Hongxun Hao

Crystals 2024, 14(6), 484; https://doi.org/10.3390/cryst14060484 - 21 May 2024

Cited by 7 | Viewed by 4261

Abstract

Growing high-quality crystals with ideal properties is of great importance. The morphology of crystal is one key factor reflecting product quality, as it can affect the performance of products and downstream operations. In this work, the current state of crystal morphology modification is [...] Read more.

Growing high-quality crystals with ideal properties is of great importance. The morphology of crystal is one key factor reflecting product quality, as it can affect the performance of products and downstream operations. In this work, the current state of crystal morphology modification is reviewed from different perspectives. First, the most widely used crystal growth models are discussed. Then, a variety of crystal morphology control methods, which include adjustment of crystallization operation parameters, addition of foreign molecules, change of different solvents, membrane assistance, the addition of external physical fields and the use of ball milling are summarized. As for applications, the control of crystal morphology has application potential in pharmaceutical and material fields, for example, energetic materials and semiconductor materials. Finally, the future development direction of crystal morphology regulation is discussed. Full article

(This article belongs to the Section Industrial Crystallization)

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14 pages, 1612 KiB

Open AccessEditor’s ChoiceReview

B-Factor Rescaling for Protein Crystal Structure Analyses

by Georg Mlynek, Kristina Djinović-Carugo and Oliviero Carugo

Crystals 2024, 14(5), 443; https://doi.org/10.3390/cryst14050443 - 7 May 2024

Cited by 8 | Viewed by 3780

Abstract

The B-factor, also known as the atomic displacement parameter, is a fundamental metric in crystallography for quantifying the positional flexibility of atoms within crystal lattices. In structural biology, various developments have expanded the use of B-factors beyond conventional crystallographic analysis, allowing for a [...] Read more.

The B-factor, also known as the atomic displacement parameter, is a fundamental metric in crystallography for quantifying the positional flexibility of atoms within crystal lattices. In structural biology, various developments have expanded the use of B-factors beyond conventional crystallographic analysis, allowing for a deeper understanding of protein flexibility, enzyme manipulation, and an improved understanding of molecular dynamics. However, the interpretation of B-factors is complicated by their sensitivity to various experimental and computational factors, necessitating rigorous rescaling methods to ensure meaningful comparisons across different structures. This article provides an in-depth description of rescaling approaches used for B-factors. It includes an examination of several methods for managing conformational disorder and selecting the atom types required for the analysis. Full article

(This article belongs to the Section Biomolecular Crystals)

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13 pages, 834 KiB

Open AccessEditor’s ChoiceReview

Possibility of Phase Transformation of Al₂O₃ by a Laser: A Review

by Tadas Matijošius, Juozas Padgurskas and Gedvidas Bikulčius

Crystals 2024, 14(5), 415; https://doi.org/10.3390/cryst14050415 - 28 Apr 2024

Cited by 2 | Viewed by 4150

Abstract

Aluminum (Al) components of high quality often require an optimal ratio of lightness and favorable mechanical properties. In order to improve the physical-mechanical properties of Al, an aluminum oxide (Al₂O₃) film is usually formed on the surface of Al, [...] Read more.

Aluminum (Al) components of high quality often require an optimal ratio of lightness and favorable mechanical properties. In order to improve the physical-mechanical properties of Al, an aluminum oxide (Al₂O₃) film is usually formed on the surface of Al, which itself is characterized by high strength, hardness, corrosion resistance, and other technical properties. Unfortunately, depending on the conditions, the oxide film may be formed from different crystal phases on the Al surface, which are not always of desirable quality, i.e., the α-Al₂O₃ phase. The present review demonstrates that the properties of the Al₂O₃ film may be improved by Al processing with a laser beam according to the scheme: Al (Al alloy) → electrochemical anodizing → treatment with laser irradiation → α-Al₂O₃. Both Al substrate and the anodizing electrolyte affect the phase transformation of anodic Al₂O₃. Laser irradiation of the Al₂O₃ surface leads to high heating and cooling rates, which may promote the formation of a highly crystalline α-Al₂O₃ phase on anodic Al₂O₃. Full article

(This article belongs to the Special Issue Progress in Light Alloys)

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14 pages, 4456 KiB

Open AccessEditor’s ChoiceArticle

The Epitaxial Growth of Ge and GeSn Semiconductor Thin Films on C-Plane Sapphire

by Emmanuel Wangila, Calbi Gunder, Petro M. Lytvyn, Mohammad Zamani-Alavijeh, Fernando Maia de Oliveira, Serhii Kryvyi, Hryhorii Stanchu, Aida Sheibani, Yuriy I. Mazur, Shui-Qing Yu and Gregory Salamo

Crystals 2024, 14(5), 414; https://doi.org/10.3390/cryst14050414 - 28 Apr 2024

Cited by 1 | Viewed by 2427

Abstract

Ge_1−xSn_x growth on a new sapphire platform has been demonstrated. This involved the growth of GeSn on Ge/GaAs layers using the algorithm developed. The resultant growths of Ge on GaAs/AlAs/sapphire and Ge_1−xSn_x on Ge/GaAs/AlAs/sapphire were investigated by [...] Read more.

Ge_1−xSn_x growth on a new sapphire platform has been demonstrated. This involved the growth of GeSn on Ge/GaAs layers using the algorithm developed. The resultant growths of Ge on GaAs/AlAs/sapphire and Ge_1−xSn_x on Ge/GaAs/AlAs/sapphire were investigated by in situ and ex situ characterization techniques to ascertain the surface morphology, crystal structure, and quality. The growth mode of Ge on GaAs was predominantly two-dimensional (2D), which signifies a layer-by-layer deposition, contributing to enhanced crystal quality in the Ge/GaAs system. The growth of Ge_1−xSn_x with 10% Sn on a graded profile for 30 min shows uniform composition and a strong peak on the reciprocal space map (RSM). On the other hand, the partially relaxed growth of the alloy on RSM was established. Full article

(This article belongs to the Special Issue Epitaxial Growth of Semiconductor Materials and Devices)

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15 pages, 3277 KiB

Open AccessEditor’s ChoiceArticle

Influence of MACl on the Crystallization Kinetics of Perovskite via a Two-Step Method

by Chenyue Wang, Bingchen He, Meirong Fu, Zhenhuang Su, Liujiang Zhang, Junhan Zhang, Bingbao Mei and Xingyu Gao

Crystals 2024, 14(5), 399; https://doi.org/10.3390/cryst14050399 - 25 Apr 2024

Cited by 2 | Viewed by 2930

Abstract

The addition of methylammonium chloride (MACl) significantly improves the performance and stability of perovskite fabricated by two-step processes. However, its role in crystallization dynamics has not been thoroughly studied. In this work, a comparison study is carried out using different additions of MACl [...] Read more.

The addition of methylammonium chloride (MACl) significantly improves the performance and stability of perovskite fabricated by two-step processes. However, its role in crystallization dynamics has not been thoroughly studied. In this work, a comparison study is carried out using different additions of MACl to investigate the impact of the perovskite crystallization dynamics. In situ grazing incidence wide-angle X-ray scattering (GIWAXS) observations during the annealing process of perovskite revealed that the amount of MACl significantly influences the crystallinity and orientation of the perovskite. Increasing the MACl addition enhances the crystallinity of the perovskite in the wet film‘s intermediate phase and strengthens the out-of-plane orientation of the FAPbI₃ perovskite α-phase (001) planes during annealing. Moreover, it was found that both excessive and insufficient amounts of MACl introduce defects into the perovskite, which are detrimental to device performance. In contrast, an optimal ratio of MACl-9 mg leads to the formation of uniform and large-grained FAPbI₃ perovskite films, with the longest carrier lifetimes (163.7 ns) compared to MACl-5 mg (68.4 ns) and MACl- 13 mg (120.1 ns). As a result, the fabricated MACl-9 mg-based solar cell achieved the highest efficiency (22.63%), which is higher than those of MACl-5 mg (21.47%) and MACl-13 mg (20.07%). Full article

(This article belongs to the Special Issue Progress and Prospects of Perovskite Films)

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11 pages, 2670 KiB

Open AccessEditor’s ChoiceArticle

A Comparison of the Mechanisms and Activation Barriers for Ammonia Synthesis on Metal Nitrides (Ta₃N₅, Mn₆N₅, Fe₃Mo₃N, Co₃Mo₃N)

by Constantinos D. Zeinalipour-Yazdi

Crystals 2024, 14(5), 392; https://doi.org/10.3390/cryst14050392 - 23 Apr 2024

Cited by 5 | Viewed by 2382

Abstract

In this study we perform a comparison of the reaction mechanism and the activation barrier for the rate-determining step in various metal nitrides (Ta₃N₅, Mn₆N₅, Fe₃Mo₃N, Co₃Mo₃N) [...] Read more.

In this study we perform a comparison of the reaction mechanism and the activation barrier for the rate-determining step in various metal nitrides (Ta₃N₅, Mn₆N₅, Fe₃Mo₃N, Co₃Mo₃N) for the ammonia synthesis reaction. The reactions are explained with simplified schematics and the energy profiles for the various reaction mechanisms are given in order to screen the catalytic activity of the catalysts for the ammonia synthesis reaction. We find that the catalytic activity ranks in the following order: Co₃Mo₃N > Fe₃Mo₃N > Ta₃N₅ > Mn₆N_5. We also find that the reaction mechanism proceeds either by a Langmuir–Hinshelwood and an Eley–Rideal/Mars–van Krevelen mechanism. This is an overview of about 10 years of computational research conducted to provide an overview of the progress established in this field of study. Full article

(This article belongs to the Special Issue Catalysts and Modeling of Ammonia Synthesis Catalytic Reactions)

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Graphical abstract

38 pages, 10149 KiB

Open AccessEditor’s ChoiceReview

Crystallization of Polymers with a Reduced Density of Entanglements

by Andrzej Pawlak

Crystals 2024, 14(4), 385; https://doi.org/10.3390/cryst14040385 - 20 Apr 2024

Cited by 8 | Viewed by 3198

Abstract

Since methods for reducing macromolecule entanglements have been developed, it has become possible to better understand the impact of polymer chain entanglement on the crystallization process. The article presents basic information about the disentangling of macromolecules and the characterization of the degree of [...] Read more.

Since methods for reducing macromolecule entanglements have been developed, it has become possible to better understand the impact of polymer chain entanglement on the crystallization process. The article presents basic information about the disentangling of macromolecules and the characterization of the degree of entanglement. The basic knowledge of polymer crystallization was also presented. Then, it was discussed how polymers crystallize during their disentangling. Non-isothermal and isothermal crystallization experiments using disentangled polymers, and for comparison using entangled polymers, are described in more detail. The influence of disentangling on both nucleation and crystal growth is highlighted. It is also shown how the crystallization of polymers changes when macromolecules re-entangle. Full article

(This article belongs to the Section Macromolecular Crystals)

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14 pages, 18119 KiB

Open AccessEditor’s ChoiceArticle

Novel Tetragonal Boron Pnictides BX (X = N, P, As, Sb, Bi) with Square B2X2 Motifs from Crystal Chemistry and First Principles

by Samir F. Matar and Vladimir L. Solozhenko

Crystals 2024, 14(4), 359; https://doi.org/10.3390/cryst14040359 - 11 Apr 2024

Viewed by 1549

Abstract

Novel tetragonal (P4₂/mnm) boron pnictides BX (X = N, P, As, Sb, Bi) with chromium boride (crb) topology exhibiting a square B2X2 motif with resulting edge- and corner-sharing tetrahedra were predicted from crystal chemistry and [...] Read more.

Novel tetragonal (P4₂/mnm) boron pnictides BX (X = N, P, As, Sb, Bi) with chromium boride (crb) topology exhibiting a square B2X2 motif with resulting edge- and corner-sharing tetrahedra were predicted from crystal chemistry and extensively characterized by density functional theory (DFT) calculations. All new BX phases were found to be cohesive with decreasing cohesive energy along the series. Mechanically stable with positive sets of elastic constants, all crb phases exhibit slightly lower hardness than other BX polymorphs due to increased openness of the crystal structures. All-positive phonon frequencies characterize the crb BX family except for X = Bi, which shows a slight acoustic instability; also, the shape of the phonon spectra changes from band-like for X = N, P, As to flat bands for the heavier elements. The electronic band structures reveal insulating to semiconducting properties for crb BX, depending on the pnictogen nature along the series. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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21 pages, 8810 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Crystal Structures of Two Crystalline Silicic Acids: Hydrated H-Apophyllite, H₁₆Si₁₆O₄₀ • 8–10 H₂O and H-Carletonite, H₃₂Si₆₄O₁₄₄

by Bernd Marler and Isabel Grosskreuz

Crystals 2024, 14(4), 326; https://doi.org/10.3390/cryst14040326 - 30 Mar 2024

Viewed by 1476

Abstract

Hydrated H-Apophyllite (HH-Apo) and H-carletonite (H-Car) were synthesized at 0 °C by leaching an apophyllite and a carletonite single crystal in a large surplus of 1.2 molar hydrochloric acid. The XRD powder patterns of HH-Apo and H-Car were indexed with space group symmetries [...] Read more.

Hydrated H-Apophyllite (HH-Apo) and H-carletonite (H-Car) were synthesized at 0 °C by leaching an apophyllite and a carletonite single crystal in a large surplus of 1.2 molar hydrochloric acid. The XRD powder patterns of HH-Apo and H-Car were indexed with space group symmetries of P4/ncc and I4/mcm and lattice parameters of a = 8.4872(2) Å, c = 16.8684(8) Å and a = 13.8972(3) Å, c = 20.4677(21) Å, respectively. The crystal structures were solved based on model building of the structures of the precursors and a physico-chemical characterization. Rietveld structure refinements confirmed the structure models. HH-Apo and H-Car are among the very few crystalline silicic acids whose structures have been determined and confirmed based on a structure refinement. The structure of HH-Apo contains thin silicate monolayers that can be regarded as constructed by rings of interconnected [SiO₃OH] tetrahedra which form a puckered silicate layer. A sheet of water molecules is intercalated between the silicate layers. There are no direct hydrogen bonds between the silanol groups, but there are hydrogen bonds of different strengths between the terminal O atoms of the silicate layers and the intercalated water molecules. The ¹H MAS NMR spectrum presents a strong signal at 4.9 ppm related to the aforementioned bonds and interactions between the water molecules, as well as a small signal at 22.5 ppm corresponding to an extremely strong hydrogen bond with d(O...O) ≈ 2.2 Å. The structure of H-Car is free of structural water and consists exclusively of microporous silicate double-layers with 4-connected [SiO₄] and 3-connected [SiO₃OH] tetrahedra in a ratio of 1:1 and a thickness of 9.2 Å. Neighboring layers are connected to each other by medium–strong hydrogen bonds with O...O distances of 2.56 Å. The structure of HH-Apo decays within several hours while H-Car is stable. A topotactic condensation reaction applied to H-Car forms an irregularly condensed silicate which still contains the layers in a distorted form as building blocks. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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20 pages, 12081 KiB

Open AccessEditor’s ChoiceArticle

Crystal Plasticity Modeling to Capture Microstructural Variations in Cold-Sprayed Materials

by Aulora Williams, YubRaj Paudel, Shiraz Mujahid, Marc Pepi, Peter Czech, Haitham El Kadiri and Hongjoo Rhee

Crystals 2024, 14(4), 329; https://doi.org/10.3390/cryst14040329 - 30 Mar 2024

Cited by 1 | Viewed by 1652

Abstract

The high-velocity impact of powder particles in cold-spray additively manufactured (CSAM) parts creates intersplat boundaries with regions of high dislocation densities and sub-grain structures. Upon microstructure and mechanical characterization, CSAM Aluminum 6061 showed non-uniformity with spatial variation in the microstructure and mechanical properties, [...] Read more.

The high-velocity impact of powder particles in cold-spray additively manufactured (CSAM) parts creates intersplat boundaries with regions of high dislocation densities and sub-grain structures. Upon microstructure and mechanical characterization, CSAM Aluminum 6061 showed non-uniformity with spatial variation in the microstructure and mechanical properties, affecting the overall response of the additively manufactured parts. Post-processing treatments are conducted in as-printed samples to improve particle bonding, relieve residual stresses, and improve mechanical properties. In this work, we attempt to implement the effects of grain size and distribution of smaller grains along the intersplat boundaries using the grain size distribution function and powder size information to accurately predict the deformation response of cold-sprayed material using a mean-field viscoplastic self-consistent (VPSC) model. The incorporation of an intersplat boundary term in the VPSC model resulted in a stress–strain response closely matching the experimental findings, preventing the superficially high stresses observed due to Hall–Petch effects from ultra-fine-grain structures. Likewise, the results from the grain analysis showed the combined effects of grain size, orientation, and intersplat mechanisms that captured the stresses experienced and strain accommodated by individual grains. Full article

(This article belongs to the Special Issue Processing-Microstructure-Properties Relationship of Advanced Alloys)

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15 pages, 11726 KiB

Open AccessEditor’s ChoiceArticle

Two New Energetic Hexagonal Anti-Perovskites (N₂H₅)₃X[B₁₂H₁₂] · H₂O (X⁻ = [NO₃]⁻ and [ClO₄]⁻): Crystal Structure, Vibrational Spectra, and Thermal Decomposition

by Rouzbeh Aghaei Hakkak, Thomas M. Klapötke and Thomas Schleid

Crystals 2024, 14(4), 310; https://doi.org/10.3390/cryst14040310 - 27 Mar 2024

Cited by 1 | Viewed by 1661

Abstract

Two novel energetic anti-perovskite compounds with the chemical formula (N₂H₅)₃X[B₁₂H₁₂] · H₂O, where X⁻ is either [NO₃]⁻ or [ClO₄]⁻, were successfully [...] Read more.

Two novel energetic anti-perovskite compounds with the chemical formula (N₂H₅)₃X[B₁₂H₁₂] · H₂O, where X⁻ is either [NO₃]⁻ or [ClO₄]⁻, were successfully synthesized. Both dodecahydro-closo-dodecaborates crystallize orthorhombically in the space group Cmc2₁, exhibiting relatively similar lattice parameters ((N₂H₅)₃[NO₃][B₁₂H₁₂] · H₂O: a = 915.94(5), b = 1817.45(9), c = 952.67(5) pm, (N₂H₅)₃[ClO₄][B₁₂H₁₂] · H₂O: a = 1040.51(6), b = 1757.68(9), c = 942.34(5) pm both for Z = 4). Their synthesis involved a two-step process: first, Cs₂[B₁₂H₁₂] passed through a cation exchange column to yield the acidic form of the dodecahydro-closo-dodecaborate, (H₃O)₂[B₁₂H₁₂]. This aqueous solution was subsequently neutralized with hydrazinium hydroxide and mixed with the corresponding water-dissolved hydrazinium salt (nitrate or perchlorate). Characterization of the obtained crystals was performed by single-crystal X-ray diffraction and Raman spectroscopy as well as thermal analyses (TG-DTA and DSC). The crystal structure determinations revealed that both compounds adopt a hexagonal anti-perovskite structure, distorted by the presence of water molecules. These compounds containing oxidizing oxoanions demonstrate a remarkable ability to release large amounts of energy (almost 2100 J/g) upon thermal decomposition. Full article

(This article belongs to the Section Materials for Energy Applications)

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10 pages, 4921 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Sputtering Target Density on the Crystal and Electronic Structure of Epitaxial BaTiO₃ Thin Films

by Fugang Qi, Shaoqin Peng, Jiachang Bi, Shunda Zhang, Guanhua Su, Peiyi Li, Jiahui Zhang, Tengteng Zhang, Weisong Zhou, Ruyi Zhang and Yanwei Cao

Crystals 2024, 14(4), 304; https://doi.org/10.3390/cryst14040304 - 26 Mar 2024

Cited by 2 | Viewed by 2300

Abstract

Barium titanate (BaTiO₃) is a promising material for silicon-integrated photonics due to its large electro-optical coefficients, low loss, high refractive index, and fast response speed. Several deposition methods have been employed to synthesize BaTiO₃ films. Magnetron sputtering is one of [...] Read more.

Barium titanate (BaTiO₃) is a promising material for silicon-integrated photonics due to its large electro-optical coefficients, low loss, high refractive index, and fast response speed. Several deposition methods have been employed to synthesize BaTiO₃ films. Magnetron sputtering is one of these methods, which offers specific advantages for growing large-scale films. However, there is a scarcity of studies investigating the effect of sputtering target density on the quality of BaTiO₃ films. Therefore, this study aims to uncover the effect of sputtering targets on the crystal and electronic structures of epitaxial BaTiO₃ thin films. Two BaTiO₃ ceramic targets were sintered at different densities by altering the sintering temperatures. The crystal structure and chemical composition of the targets were then characterized using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Subsequently, BaTiO₃ epitaxial films were grown by magnetron sputtering using these two targets. The crystal and electronic structures of the BaTiO₃ films were analyzed using high-resolution X-ray diffraction, X-ray photoemission spectroscopy, atomic force microscopy, and spectroscopic ellipsometry. Notably, the BaTiO₃ films grown with high-density targets show superior quality but contain oxygen vacancies, whereas those films synthesized with low-density targets display high surface roughness. These findings provide insights into the effect of sputtering target density on the crystal and electronic structures of epitaxial BaTiO₃ thin films. Full article

(This article belongs to the Special Issue Epitaxial Growth and Application of Metallic Oxide Thin Films)

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26 pages, 3846 KiB

Open AccessEditor’s ChoiceReview

Nanostructured Materials for Enhanced Performance of Solid Oxide Fuel Cells: A Comprehensive Review

by Hicham Helal, Mohammadi Ahrouch, Abdelaziz Rabehi, Dario Zappa and Elisabetta Comini

Crystals 2024, 14(4), 306; https://doi.org/10.3390/cryst14040306 - 26 Mar 2024

Cited by 16 | Viewed by 3450

Abstract

Solid oxide fuel cells (SOFCs) have emerged as promising candidates for efficient and environmentally friendly energy conversion technologies. Their high energy conversion efficiency and fuel flexibility make them particularly attractive for various applications, ranging from stationary power generation to portable electronic devices. Recently, [...] Read more.

Solid oxide fuel cells (SOFCs) have emerged as promising candidates for efficient and environmentally friendly energy conversion technologies. Their high energy conversion efficiency and fuel flexibility make them particularly attractive for various applications, ranging from stationary power generation to portable electronic devices. Recently, research has focused on utilizing nanostructured materials to enhance the performance of SOFCs. This comprehensive review summarizes the latest advancements in the design, fabrication, and characterization of nanostructured materials integrated in SOFC. The review begins by elucidating the fundamental principles underlying SOFC operation, emphasizing the critical role of electrode materials, electrolytes, and interfacial interactions in overall cell performance, and the importance of nanostructured materials in addressing key challenges. It provides an in-depth analysis of various types of nanostructures, highlighting their roles in improving the electrochemical performance, stability, and durability of SOFCs. Furthermore, this review delves into the fabrication techniques that enable precise control over nanostructure morphology, composition, and architecture. The influence of nanoscale effects on ionic and electronic transport within the electrolyte and electrodes is thoroughly explored, shedding light on the mechanisms behind enhanced performance. By providing a comprehensive overview of the current state of research on nanostructured materials for SOFCs, this review aims to guide researchers, engineers, and policymakers toward the development of high-performance, cost-effective, and sustainable energy conversion systems. Full article

(This article belongs to the Special Issue Advances of Solid Oxide Fuel Cells)

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16 pages, 4641 KiB

Open AccessEditor’s ChoiceArticle

The Impact of Grain Growth on the Functional Properties in Room-Temperature Powder Aerosol Deposited Free-Standing (Ba,Ca)(Zr,Ti)O₃ Thick Films

by Juliana G. Maier, Tim Fuggerer, Daisuke Urushihara, Alexander Martin, Neamul H. Khansur, Ken-ichi Kakimoto and Kyle G. Webber

Crystals 2024, 14(4), 296; https://doi.org/10.3390/cryst14040296 - 22 Mar 2024

Viewed by 1887

Abstract

This study investigates the development of freestanding thick films (FSFs) of lead-free (Ba,Ca)(Zr,Ti)O₃ and the role of grain growth on the electromechanical response. During deposition, room temperature powder aerosol deposition rapidly produces thick films with a nano-grain structure that limits the electromechanical [...] Read more.

This study investigates the development of freestanding thick films (FSFs) of lead-free (Ba,Ca)(Zr,Ti)O₃ and the role of grain growth on the electromechanical response. During deposition, room temperature powder aerosol deposition rapidly produces thick films with a nano-grain structure that limits the electromechanical properties. In this study, the films are removed from the substrate using a sacrificial buffering layer to avoid thermal treatment and allow for an initial as-processed state. Following this, FSFs were thermally treated at various annealing temperatures from 800 °C to 1400 °C to induce grain growth, which was characterized with scanning and transmission electron microscopy. X-ray diffraction revealed an increase in the crystallite size consistent with an increase in grain size and a decrease in internal residual stress. The temperature-dependent dielectric behavior and the large-field ferroelectric response were also characterized, revealing significant differences of the FSFs from the bulk properties. Full article

(This article belongs to the Special Issue Advanced Ferroelectric, Piezoelectric and Dielectric Ceramics)

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10 pages, 1429 KiB

Open AccessEditor’s ChoiceArticle

Revisiting the Crystallography of {225}_γ Martensite: How EBSD Can Help to Solve Long-Standing Controversy

by Loïc Malet and Stéphane Godet

Crystals 2024, 14(3), 287; https://doi.org/10.3390/cryst14030287 - 20 Mar 2024

Viewed by 1545

Abstract

Explaining the crystallography of iron alloys martensite with a {225}_γ habit plane remains a challenging task within the phenomenological theory of martensite crystallography. The purpose of this study is to re-examine the martensite formed in a Fe-8Cr-1.1C alloy using EBSD, which has [...] Read more.

Explaining the crystallography of iron alloys martensite with a {225}_γ habit plane remains a challenging task within the phenomenological theory of martensite crystallography. The purpose of this study is to re-examine the martensite formed in a Fe-8Cr-1.1C alloy using EBSD, which has a better angular resolution than the conventional transmission electron diffraction techniques previously used. The results show that the single morphological plates, which hold a near {225}_γ habit plane, are bivariant composites made up of two twin-related variants. It is shown that a {113}_γ plane is systematically parallel to one of the three common

{\{112\}}_{α}

planes between the two twin-related crystals. This observation suggests that the lattice invariant strain of transformation occurs through a dislocation glide on the {113}_γ ⟨110⟩_γ system, rather than through twinning as is commonly accepted. Based on this assumption, the predictions of Bowles and Mackenzie’s original theory are in good agreement with the crystallographic features of {225}_γ martensite. Unexpectedly, it is the high shear solution of the theory that gives the most accurate experimental predictions. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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12 pages, 3561 KiB

Open AccessEditor’s ChoiceArticle

Comparative Analysis of Room Temperature Structures Determined by Macromolecular and Serial Crystallography

by Ki Hyun Nam

Crystals 2024, 14(3), 276; https://doi.org/10.3390/cryst14030276 - 14 Mar 2024

Cited by 7 | Viewed by 2308

Abstract

Temperature directly influences the function and structure of proteins. Crystal structures determined at room temperature offer more biologically relevant structural information regarding flexibility, rigidity, and thermal motion than those determined by conventional cryocrystallography. Crystal structures can be determined at room temperature using conventional [...] Read more.

Temperature directly influences the function and structure of proteins. Crystal structures determined at room temperature offer more biologically relevant structural information regarding flexibility, rigidity, and thermal motion than those determined by conventional cryocrystallography. Crystal structures can be determined at room temperature using conventional macromolecular crystallography (MX) or serial crystallography (SX) techniques. Among these, MX may theoretically be affected by radiation damage or X-ray heating, potentially resulting in differences between the room temperature structures determined by MX and SX, but this has not been fully elucidated. In this study, the room temperature structure of xylanase GH11 from Thermoanaerobacterium saccharolyticum was determined by MX (RT-TsaGH11-MX). The RT-TsaGH11-MX exhibited both the open and closed conformations of the substrate-binding cleft within the β-sandwich fold. The RT-TsaGH11-MX showed distinct structural changes and molecular flexibility when compared with the RT-TsaGH11 determined via serial synchrotron crystallography. The notable molecular conformation and flexibility of the RT-TsaGH11-MX may be induced by radiation damage and X-ray heating. These findings will broaden our understanding of the potential limitations of room temperature structures determined by MX. Full article

(This article belongs to the Section Macromolecular Crystals)

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13 pages, 6547 KiB

Open AccessEditor’s ChoiceReview

Floating Zone Growth of Pure and Pb-Doped Bi-2201 Crystals

by Maria Roslova, Bernd Büchner and Andrey Maljuk

Crystals 2024, 14(3), 270; https://doi.org/10.3390/cryst14030270 - 11 Mar 2024

Cited by 2 | Viewed by 2058

Abstract

In this review, we summarize recent progress in crystal growth and understanding of the influence of crystal structure on superconductivity in pure and Pb-doped Bi₂Sr₂CuO_y (Bi-2201) materials belonging to the overdoped region of high-temperature cuprate superconductors. The crystal [...] Read more.

In this review, we summarize recent progress in crystal growth and understanding of the influence of crystal structure on superconductivity in pure and Pb-doped Bi₂Sr₂CuO_y (Bi-2201) materials belonging to the overdoped region of high-temperature cuprate superconductors. The crystal growth of Bi-2201 superconductors faces challenges due to intricate materials chemistry and the lack of knowledge of corresponding phase diagrams. Historically, a crucible-free floating zone method emerged as the most promising growth approach for these materials, resulting in high-quality single crystals. This review outlines the described methods in the literature and the authors’ synthesis endeavors encompassing Pb-doped Bi-2201 crystals, provides a detailed structural characterization of as-grown and post-growth annealed samples, and highlights optimal growth conditions that yield large-size, single-phase, and compositionally homogeneous Bi-2201 single crystals. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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30 pages, 11194 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Exploring Various Crystal and Molecular Structures of Gabapentin—A Review

by Justyna Baranowska and Łukasz Szeleszczuk

Crystals 2024, 14(3), 257; https://doi.org/10.3390/cryst14030257 - 6 Mar 2024

Cited by 3 | Viewed by 4221

Abstract

Novel antiepileptic drugs have been developed at an unparalleled rate during the past 15 years. Gabapentin (GBP), which was approved for the treatment of refractory localization-related epilepsies in the U.K. and Europe in 1993, was one of the first drugs to come out [...] Read more.

Novel antiepileptic drugs have been developed at an unparalleled rate during the past 15 years. Gabapentin (GBP), which was approved for the treatment of refractory localization-related epilepsies in the U.K. and Europe in 1993, was one of the first drugs to come out of this era. Since then, GBP has become well-known across the world, not only for its antiepileptic qualities but also for its effectiveness in the treatment of chronic pain disorders, particularly neuropathic pain. In this review, the crystal structures of GBP and GBP-related compounds have been analyzed and compared. Particular attention has been paid to the polymorphism of GBP and its hydrates, their thermodynamic stability, and conformational differences. In addition, the puckering parameters for the cyclohexane ring of a total of 118 molecules of GBP found in the analyzed crystal structures have been calculated and analyzed. The results of recent high-pressure crystallization studies and quantum chemical calculations indicate that the entire landscape of GBP has not been revealed yet. Full article

(This article belongs to the Special Issue Structural Studies in Drug Discovery and Development: From the Lead to the Pharmaceutical Form)

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11 pages, 8080 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Crystal Structures of Rhomb-Shaped Dimeric Pd(II) Complexes with Arylethynyl-Substituted 2,2′-Bipyridine through CH⋯π Interactions in the Crystalline States

by Akiko Hori, Reo Ichisugi, Daiki Azegami, Naoki Toyama and Hidetaka Yuge

Crystals 2024, 14(3), 255; https://doi.org/10.3390/cryst14030255 - 5 Mar 2024

Cited by 3 | Viewed by 1487

Abstract

Two molecular structures of a complex C₂₆H₁₆Cl₂N₂Pd (1) with a benzene hemisolvate (1•0.5C₆H₆) and a complex C₃₄H₂₀Cl₂N₂Pd (2 [...] Read more.

Two molecular structures of a complex C₂₆H₁₆Cl₂N₂Pd (1) with a benzene hemisolvate (1•0.5C₆H₆) and a complex C₃₄H₂₀Cl₂N₂Pd (2) revealed similar conformations: one side of the arylethynyl group is flat to the bipyridine plane while the other side of the arylethynyl group is highly twisted to the plane because rhomb-like dimer fragments are formed between respective two complexes through CH⋯π interactions. The Hirshfeld surface analysis indicates that the most important contributions for the crystal packing of 1 are from H⋯H (33.6%), C⋯H/H⋯C (28.3%), Cl⋯H/H⋯Cl (17.8%), and C⋯C (10.6%) interactions and those of 2 are from H⋯H (36.5%), C⋯H/H⋯C (26.0%), Cl⋯H/H⋯Cl (15.7%), and C⋯C (12.3%) interactions, indicating the remarkable CH⋯π and electron distribution of molecules by Cl ions. The benzene solvate molecule of 1•0.5C₆H₆ performs to fill the internal space instead of the naphthyl group. Detailed crystallographic and DFT studies were performed to understand the molecular structures and the corresponding supramolecular associations. Full article

(This article belongs to the Section Organic Crystalline Materials)

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14 pages, 4766 KiB

Open AccessEditor’s ChoiceArticle

Investigation into the Effects of Cross-Sectional Shape and Size on the Light-Extraction Efficiency of GaN-Based Blue Nanorod Light-Emitting Diode Structures

by Bohae Lee and Han-Youl Ryu

Crystals 2024, 14(3), 241; https://doi.org/10.3390/cryst14030241 - 29 Feb 2024

Cited by 2 | Viewed by 1917

Abstract

We investigated the effect of cross-sectional shape and size on the light-extraction efficiency (LEE) of GaN-based blue nanorod light-emitting diode (LED) structures using numerical simulations based on finite-difference time-domain methods. For accurate determination, the LEE and far-field pattern (FFP) were evaluated by averaging [...] Read more.

We investigated the effect of cross-sectional shape and size on the light-extraction efficiency (LEE) of GaN-based blue nanorod light-emitting diode (LED) structures using numerical simulations based on finite-difference time-domain methods. For accurate determination, the LEE and far-field pattern (FFP) were evaluated by averaging them over emission spectra, polarization, and source positions inside the nanorod. The LEE decreased as rod size increased, owing to the nanorods’ increased ratio of cross-sectional area to sidewall area. We compared circular, square, triangular, and hexagonal cross-sectional shapes in this study. To date, nanorod LEDs with circular cross sections have been mainly demonstrated experimentally. However, circular shapes were found to show the lowest LEE, which is attributed to the coupling with whispering-gallery modes. For the total emission of the nanorod, the triangular cross section exhibited the highest LEE. When the angular dependence of the LEE was calculated using the FFP simulation results, the triangular and hexagonal shapes showed relatively high LEEs for direction emission. The simulation results presented in this study are expected to be useful in designing high-efficiency nanorod LED structures with optimum nanorod shape and dimensions. Full article

(This article belongs to the Special Issue Group-III Nitride Quantum Wells)

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19 pages, 7580 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hydrate Formation with the Memory Effect Using Classical Nucleation Theory

by I. Yucel Akkutlu, Emre Arslan and Faisal Irshad Khan

Crystals 2024, 14(3), 243; https://doi.org/10.3390/cryst14030243 - 29 Feb 2024

Viewed by 1634

Abstract

Methane hydrate formation is analytically studied in the presence of the water memory effect using the classical nucleation theory. The memory effect is introduced as a change in nucleation site from a three-dimensional heterogenous nucleation on a solid surface with cap-shaped hydrate clusters [...] Read more.

Methane hydrate formation is analytically studied in the presence of the water memory effect using the classical nucleation theory. The memory effect is introduced as a change in nucleation site from a three-dimensional heterogenous nucleation on a solid surface with cap-shaped hydrate clusters (3D-HEN) to a two-dimensional nucleation on the solid hydrate residue surface with monolayer disk-shaped hydrate clusters (2D-NOH). The analysis on the stationary nucleation of methane hydrate under isobaric conditions shows that the memory effect caused an average decrease of 4.4 K in metastable zone width, or subcooling. This decrease can be erased at higher dissociation temperatures (ΔT > 17.2 K) due to a decrease in the concentration of 2D-NOH nucleation sites. Moreover, the probability of hydrate formation is estimated for the purpose of quantifying risk associated with methane hydrate formation in the presence of the memory effect. Full article

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14 pages, 10069 KiB

Open AccessEditor’s ChoiceArticle

Crystalline Microstructure, Microsegregations, and Mechanical Properties of Inconel 718 Alloy Samples Processed in Electromagnetic Levitation Facility

by Yindong Fang, Chu Yu, Nikolai Kropotin, Martin Seyring, Katharina Freiberg, Matthias Kolbe, Stephanie Lippmann and Peter K. Galenko

Crystals 2024, 14(3), 244; https://doi.org/10.3390/cryst14030244 - 29 Feb 2024

Cited by 2 | Viewed by 1610

Abstract

The solidification of Inconel 718 alloy (IN718) from undercooled liquid is studied. The solidification kinetics is evaluated in melted and undercooled droplets processed using the electromagnetic levitation (EML) technique by the temperature–time profiles and solid/liquid (S/L) interface movement during recalescence. The kinetics is [...] Read more.

The solidification of Inconel 718 alloy (IN718) from undercooled liquid is studied. The solidification kinetics is evaluated in melted and undercooled droplets processed using the electromagnetic levitation (EML) technique by the temperature–time profiles and solid/liquid (S/L) interface movement during recalescence. The kinetics is monitored in real time by special pyrometrical measurements and high-speed digital camera. It is shown that the growth velocity of

γ

-phase (the primary phase in IN718), the final crystalline microstructure (dendritic and grained), and the mechanical properties (microhardness) are strongly dependent on the initial undercooling

Δ T

at which the samples started to solidify with the originating

γ

-phase. Particularly, with the increase in undercooling, the secondary dendrite arm spacing decreases from 28 μm to 5 μm. At small and intermediate ranges of undercooling, the solidified droplets have a dendritic crystalline microstructure. At higher undercooling values reached in the experiment,

Δ T > 160

K (namely, for samples solidified with

Δ T = 170

K and

Δ T = 263

K), fine crystalline grains are observed instead of the dendritic structure of solidified drops. Such change in the crystalline morphology is qualitatively consistent with the behavior of crystal growth kinetics which exhibits the change from the power law to linear law at

Δ T \approx 160

K in the velocity–undercooling relationship (measured by the advancement of the recalescence front in solidifying droplets). Study of the local mechanical properties shows that the microhardness increases with the increase in the

γ^{″}

-phase within interdendritic spacing. The obtained data are the basis for testing the theoretical and computational of multicomponent alloy samples. Full article

(This article belongs to the Special Issue Phase Transition in External Fields (2nd Edition))

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31 pages, 9156 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Review on Crystallization Strategies for Polymer Single Crystals

by Tianyu Wu, Jun Xu and Haimu Ye

Crystals 2024, 14(3), 207; https://doi.org/10.3390/cryst14030207 - 22 Feb 2024

Cited by 5 | Viewed by 7651

Abstract

Polymer physics has evolved significantly over the past century, transitioning from the early recognition of the chain structure of polymers to a mature field integrating principles from statistical mechanics, thermodynamics, and condensed matter physics. As an important part of polymer physics, polymer single [...] Read more.

Polymer physics has evolved significantly over the past century, transitioning from the early recognition of the chain structure of polymers to a mature field integrating principles from statistical mechanics, thermodynamics, and condensed matter physics. As an important part of polymer physics, polymer single crystals are crucial for understanding molecular structures and behaviors, enhancing material properties, and enabling precise functionalization. They offer insights into polymer crystallization kinetics, serve as templates for nanofabrication, and have applications in electronics, sensors, and biomedical fields. However, due to the complexity of molecular chain movement, the formation of polymer single crystals is still very difficult. Over the decades, numerous researchers have dedicated themselves to unraveling the mysteries of polymer single crystals, yielding substantial findings. This paper focus on the historical evolution and advancements in polymer single crystal research, aiming to offer valuable insights and assistance to fellow researchers in this field. Full article

(This article belongs to the Special Issue Advanced Research on Macromolecular Crystals (2nd Edition))

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12 pages, 3502 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Role of Diamonds Dispersed in Ferronematic Liquid Crystals on Structural Properties

by Peter Bury, Marek Veveričík, František Černobila, Natália Tomašovičová, Veronika Lacková, Katarína Kónyová, Ivo Šafařík, Viktor Petrenko, Oleksandr Tomchuk, Milan Timko and Peter Kopčanský

Crystals 2024, 14(3), 202; https://doi.org/10.3390/cryst14030202 - 20 Feb 2024

Cited by 1 | Viewed by 1573

Abstract

A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe₃O₄ nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe₃O₄ magnetic nanoparticles and additionally bound to [...] Read more.

A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe₃O₄ nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe₃O₄ magnetic nanoparticles and additionally bound to diamond nanoparticles (DNPs), of a volume concentration of 3.2 mg/mL, 1.6 mg/mL and 0.32 mg/mL, were investigated using both magneto-optical effect and surface acoustic waves (SAWs) to study the role of diamond nanoparticles on the structural properties of ferronematic liquid crystals. The responses of light transmission and SAW attenuation to an external magnetic field were investigated experimentally under a linearly increasing and decreasing magnetic field, respectively. Investigations of the phase transition temperature shift of individual composites were also performed. The experimental results highlighted a decrease in the threshold field in the ferronematic LC composites compared to the pure 5CB as well as its further decrease after mixing Fe₃O₄ with diamond powder. Concerning the transition temperature, its increase with an increase in the volume fraction of both kinds of nanoparticles was registered. The role of diamond nanoparticles in the structural changes and the large residual light transition and/or attenuation (memory effect) were also observed. The presented results confirmed the potential of diamond nanoparticles in nematic composites to modify their properties which could lead to final applications. Full article

(This article belongs to the Section Liquid Crystals)

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14 pages, 4544 KiB

Open AccessEditor’s ChoiceArticle

The Crystal Structure and Physicochemical Properties of New Complexes Containing a Cu^II-Ln^III-Cu^II Core

by Beata Cristóvão, Dariusz Osypiuk and Barbara Mirosław

Crystals 2024, 14(2), 189; https://doi.org/10.3390/cryst14020189 - 14 Feb 2024

Cited by 1 | Viewed by 1861

Abstract

Three new cationic complexes, [Cu₄Tb₂(H₂L)₄(NO₃)₄(H₂O)₃](NO₃)₂·5.5H₂O·2MeOH (1), [Cu₄Ho₂(H₂L)₄(NO₃)₄(H [...] Read more.

Three new cationic complexes, [Cu₄Tb₂(H₂L)₄(NO₃)₄(H₂O)₃](NO₃)₂·5.5H₂O·2MeOH (1), [Cu₄Ho₂(H₂L)₄(NO₃)₄(H₂O)₃](NO₃)₂·7.5H₂O (2), and [Cu₄Er₂(H₂ L)₄(NO₃)₄(H₂O)₃](NO₃)₂·7H₂O·3MeOH (3), were synthesized and studied using elemental and TG/DTG/DSC analyses, single-crystal X-ray diffraction, and magnetic measurements. The structure analysis showed that 1–3 crystallize as (NO₃)-bridged compounds and that the lanthanide(III) ion acts as a joint connecting two [CuH₂L] coordination units. In each heterotrinuclear unit, an asymmetry in the degree of planarity of the bridging CuO₂Ln fragments is observed. The Cu^II ions are five- and six-coordinate, with distorted square pyramidal and octahedral geometry, respectively, whereas the Ln^III ions are nine-coordinate. The solvates 1–3 are stable at room temperature, and their desolvation process is consistent with the loss of water and/or methanol molecules. The temperature dependence of the magnetic susceptibility and the field-dependent magnetization indicate the weak ferromagnetic interaction between the paramagnetic centers Cu^II and Tb^III/Ho^III 1 and 2. Full article

(This article belongs to the Special Issue Feature Papers in Crystals 2023)

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12 pages, 3721 KiB

Open AccessEditor’s ChoiceArticle

Combining a Drug and a Nutraceutical: A New Cocrystal of Praziquantel and Curcumin

by Camila Caro Garrido, Marie Vandooren, Koen Robeyns, Damien P. Debecker, Patricia Luis and Tom Leyssens

Crystals 2024, 14(2), 181; https://doi.org/10.3390/cryst14020181 - 11 Feb 2024

Cited by 4 | Viewed by 2574

Abstract

This study explores the co-crystallization between the drug praziquantel (PZQ) and the nutraceutical curcumin (CU). The investigation revealed two novel solid forms: a cocrystal solvate with ethyl acetate and a non-solvated cocrystal. This novel drug–nutraceutical cocrystal is a praziquantel–curcumin (2:1) cocrystal. The cocrystal [...] Read more.

This study explores the co-crystallization between the drug praziquantel (PZQ) and the nutraceutical curcumin (CU). The investigation revealed two novel solid forms: a cocrystal solvate with ethyl acetate and a non-solvated cocrystal. This novel drug–nutraceutical cocrystal is a praziquantel–curcumin (2:1) cocrystal. The cocrystal solvate has ethyl acetate molecules occupying the voids with minimal interactions within the crystal lattice. The application of heat treatment induces solvent removal and prompts the transition to the non-solvated cocrystal, as highlighted by variable-temperature X-ray powder diffraction (VT-XRPD). Thermal analyses demonstrate the stability of the cocrystal solvate up to approximately 100 °C, beyond which it transforms into the non-solvated phase, which eventually melts at 130 °C. Full article

(This article belongs to the Special Issue Feature Papers in Crystals 2023)

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14 pages, 3787 KiB

Open AccessEditor’s ChoiceArticle

Investigating Influential Parameters for High-Purity Germanium Crystal Growth

by Sanjay Bhattarai, Dongming Mei, Narayan Budhathoki, Kunming Dong and Austin Warren

Crystals 2024, 14(2), 177; https://doi.org/10.3390/cryst14020177 - 10 Feb 2024

Viewed by 2754

Abstract

This paper focuses on the research and development of high-purity germanium (HPGe) crystals for detector fabrication, specifically targeting applications in rare-event physics searches. The primary objective was to produce large-scale germanium crystals weighing >1 kg with a controlled diameter of ∼10 cm and [...] Read more.

This paper focuses on the research and development of high-purity germanium (HPGe) crystals for detector fabrication, specifically targeting applications in rare-event physics searches. The primary objective was to produce large-scale germanium crystals weighing >1 kg with a controlled diameter of ∼10 cm and an impurity range of approximately

10^{10}

/cm

^{3}

. Ensuring structural integrity and excellent crystalline quality requires a thorough assessment of dislocation density, a critical aspect of the crystal development process. Dislocation density measurements play a crucial role in maximizing the sensitivity of HPGe detectors, and our findings confirmed that the dislocation density fell within acceptable ranges for detector fabrication. Additionally, this paper examines the segregation coefficient of various contaminants during the crystal development process. Comprehensive analysis of impurity segregation is essential for reducing contaminant quantities in the crystal lattice and customizing purification processes. This, in turn, minimizes undesired background noise, enhancing signal-to-noise ratios for rare-event physics searches and overall detector performance. The investigation included the segregation coefficients of three major acceptors and one donor in crystals grown at the University of South Dakota, providing valuable insights for optimizing crystal purity and detector efficiency. Full article

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18 pages, 7567 KiB

Open AccessEditor’s ChoiceArticle

Numerical Microstructure Prediction for Lattice Structures Manufactured by Electron Beam Powder Bed Fusion

by Johannes A. Koepf, Julian Pistor, Matthias Markl and Carolin Körner

Crystals 2024, 14(2), 149; https://doi.org/10.3390/cryst14020149 - 31 Jan 2024

Cited by 4 | Viewed by 1588

Abstract

The latest advances in additive manufacturing have given rise to an increasing interest in additively built lattice structures due to their superior properties compared to foams and honeycombs. The foundation of these superior properties is a tailored microstructure, which is difficult to achieve [...] Read more.

The latest advances in additive manufacturing have given rise to an increasing interest in additively built lattice structures due to their superior properties compared to foams and honeycombs. The foundation of these superior properties is a tailored microstructure, which is difficult to achieve in additive manufacturing because of the variety of process parameters influencing the quality of the final part. This work presents the numerical prediction of the resulting grain structure of a lattice structure additively built by electron beam powder bed fusion. A thermal finite-difference model is coupled to a sophisticated cellular automaton-based crystal growth model, including nucleation. Numerically predicted grain structures, considering different nucleation conditions, are compared with experimentally derived EBSD measurements. The comparison reveals that nucleation is important, especially in fine lattice structures. The developed software, utilizing the nucleation model, is finally able to predict the as-built grain structure in lattice structures. Full article

(This article belongs to the Special Issue Crystallization Process and Simulation Calculation, Second Edition)

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22 pages, 8785 KiB

Open AccessEditor’s ChoiceArticle

Insights in the Structural Hierarchy of Statically Crystallized Palm Oil

by Fien De Witte, Ivana A. Penagos, Kato Rondou, Kim Moens, Benny Lewille, Daylan A. Tzompa-Sosa, Davy Van de Walle, Filip Van Bockstaele, Andre G. Skirtach and Koen Dewettinck

Crystals 2024, 14(2), 142; https://doi.org/10.3390/cryst14020142 - 30 Jan 2024

Cited by 7 | Viewed by 2478

Abstract

Palm oil (PO) is still widely used for the production of all types of food products. Due to its triacylglycerol (TG) composition, PO is semisolid at ambient temperature, offering possibilities for many applications. In order to tailor the fat crystal network for certain [...] Read more.

Palm oil (PO) is still widely used for the production of all types of food products. Due to its triacylglycerol (TG) composition, PO is semisolid at ambient temperature, offering possibilities for many applications. In order to tailor the fat crystal network for certain applications, it remains imperative to understand the structural build-up of the fat crystal network at the full-length scale and to understand the effect of processing conditions. In this study, PO was crystallized under four temperature protocols (fast (FC) or slow (SC) cooling to 20 °C or 25 °C) and was followed for one hour of isothermal time. A broad toolbox was used to fundamentally unravel the structural build-up of the fat crystal network at different length scales. Wide-angle and small-angle X-ray scattering (WAXS and SAXS) showed transitions from α-2L to β’-2L over time. Despite the presence of the same polymorphic form (β’), chain length structure (2L), and domain size, ultra-small-angle X-ray scattering (USAXS) showed clear differences in the mesoscale. For all samples, the lamellar organization was confirmed. Both cooling speed and isothermal temperature were found to affect the size of the crystal nanoplatelets (CNPs), where the highest cooling speed and lowest isothermal temperature (FC and 20 °C) created the smallest CNPs. The microstructure was visualized with polarized light microscopy (PLM) and cryo-scanning electron microscopy (cryo-SEM), showing clear differences in crystallite size, clustering, and network morphology. Raman spectroscopy was applied to confirm differences in triglyceride distribution in the fat crystal network. This study shows that both cooling rate and isothermal temperature affect the fat crystal network formed, especially at the meso- and microscale. Full article

(This article belongs to the Special Issue Feature Papers in Crystals 2023)

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20 pages, 7575 KiB

Open AccessEditor’s ChoiceArticle

Lattice Parameter Evolution during the β-to-α and β-to-ω Transformations of Iron- and Aluminum-Modified Ti-11Cr(at.%)

by JoAnn Ballor, Jonathan D. Poplawsky, Arun Devaraj, Scott Misture and Carl J. Boehlert

Crystals 2024, 14(2), 145; https://doi.org/10.3390/cryst14020145 - 30 Jan 2024

Cited by 2 | Viewed by 2121

Abstract

β-titanium (β-Ti) alloys are useful in diverse industries because their mechanical properties can be tuned by transforming the metastable β phase into other metastable and stable phases. Relationships between lattice parameter and β-Ti alloy concentrations have been explored, but the lattice parameter evolution [...] Read more.

β-titanium (β-Ti) alloys are useful in diverse industries because their mechanical properties can be tuned by transforming the metastable β phase into other metastable and stable phases. Relationships between lattice parameter and β-Ti alloy concentrations have been explored, but the lattice parameter evolution during β-phase transformations is not well understood. In this work, the β-Ti alloys, Ti-11Cr, Ti-11Cr-0.85Fe, Ti-11Cr-5.3Al, and Ti-11Cr-0.85Fe-5.3Al (all in at.%), underwent a 400 °C aging treatment for up to 12 h to induce the β-to-ω and β-to-α phase transformations. Phase identification and lattice parameters were measured in situ using high-temperature X-ray diffraction. Phase compositions were measured ex situ using atom probe tomography. During the phase transformations, Cr and Fe diffused from the ω and α phases into the β matrix, and the β-phase lattice parameter exhibited a corresponding decrease. The decrease in β-phase lattice parameter affected the α- and ω-phase lattice parameters. The α phase in the Fe-free alloys exhibited α-phase c/a ratios close to those of pure Ti. A larger β-phase composition change in Ti-11Cr resulted in larger ω-phase lattice parameter changes than that for Ti-11Cr-0.85Fe. This work illuminates the complex relationship between diffusion, composition, and structure for these diffusive/displacive transformations. Full article

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21 pages, 10223 KiB

Open AccessEditor’s ChoiceArticle

Kinetics and Thermodynamics of the Phase Transformation in the Nanocrystalline Substance—Gas Phase System

by Walerian Arabczyk, Rafał Pelka, Bartłomiej Wilk and Zofia Lendzion-Bieluń

Crystals 2024, 14(2), 129; https://doi.org/10.3390/cryst14020129 - 27 Jan 2024

Cited by 2 | Viewed by 1292

Abstract

This study presents a model of the reaction of a nanocrystalline substance within the gas phase, where diffusion of gas reactants in the volume of the nanocrystallites is a rate-limiting step. According to the model calculations carried out, the rate of diffusion across [...] Read more.

This study presents a model of the reaction of a nanocrystalline substance within the gas phase, where diffusion of gas reactants in the volume of the nanocrystallites is a rate-limiting step. According to the model calculations carried out, the rate of diffusion across the phase boundary located on the nanocrystallite surface limits the rate of the process. It was stated that in chemical processes with a phase transformation, the critical concentration of absorbate depends on two factors: the specific active surface area of the adsorbent and the difference in chemical potentials between the gas phase and the equilibrium potential at which the phase transformation occurs. When the actual adsorbate potential in the gas phase is much greater than the equilibrium potential of the nanocrystallite with the largest specific active surface, nanocrystallites undergo phase changes in the order according to their specific active surfaces from the largest to the smallest. In a process where the actual adsorbate potential is close to an equilibrium one, nanocrystallites undergo phase transformation in the order of their specific active surface from the smallest to the largest. Full article

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16 pages, 2497 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Halogen Bonding versus Nucleophilic Substitution in the Co-Crystallization of Halomethanes and Amines

by Olivia Grounds, Matthias Zeller and Sergiy V. Rosokha

Crystals 2024, 14(2), 124; https://doi.org/10.3390/cryst14020124 - 26 Jan 2024

Cited by 3 | Viewed by 1985

Abstract

Haloalkanes and amines are common halogen-bond (XB) donors and acceptors as well as typical reagents in nucleophilic substitution reactions. Thus, crystal engineering using these molecules requires an understanding of the interchange between these processes. Indeed, we previously reported that the interaction of quinuclidine [...] Read more.

Haloalkanes and amines are common halogen-bond (XB) donors and acceptors as well as typical reagents in nucleophilic substitution reactions. Thus, crystal engineering using these molecules requires an understanding of the interchange between these processes. Indeed, we previously reported that the interaction of quinuclidine (QN) with CHI₃ in acetonitrile yielded co-crystals showing a XB network of these two constituents. In the current work, the interactions of QN with C₂H₅I or 1,4-diazabicyclo[2.2.2]octane (DABCO) with CH₂I₂ led to nucleophilic substitution producing I⁻ anions and quaternary ammonium (QN-CH₂CH₃ or DABCO-CH₂I⁺) cations. Moreover, the reaction of QN with CHI₃ in dichloromethane afforded co-crystals containing XB networks of CHI₃ with either Cl⁻ or I⁻ anions and QN-CH₂Cl⁺ counter-ions. A similar reaction in acetone produced XB networks comprising CHI₃, I⁻ and QN-CH₂COCH₃⁺. These distinctions were rationalized through a computational analysis of XB complexes and the transition-state energies for the nucleophilic substitution. It indicated that the outcome of the reactions was determined mostly by the relative energies of the products. The co-crystals obtained in this work showed bonding between the cationic (DABCO-CH₂I⁺, QN-CH₂Cl⁺) or neutral (CHI₃) XB donors and the anionic (I⁻, Cl⁻) or neutral (CHI₃) acceptors. Their analysis showed comparable electron and energy densities at the XB bond critical points and similar XB energies regardless of the charges of the interacting species. Full article

(This article belongs to the Special Issue Feature Papers in Crystals 2023)

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29 pages, 14422 KiB

Open AccessEditor’s ChoiceReview

Advances in Ultrasonic-Assisted Directed Energy Deposition (DED) for Metal Additive Manufacturing

by Wenjun Zhang, Chunguang Xu, Cencheng Li and Sha Wu

Crystals 2024, 14(2), 114; https://doi.org/10.3390/cryst14020114 - 24 Jan 2024

Cited by 14 | Viewed by 5075

Abstract

Directed Energy Deposition (DED), a branch of AM processes, has emerged as a significant technique for fabricating large metal components in sectors such as aerospace, automotive, and healthcare. DED is characterized by its high deposition rate and scalability, which stand out among other [...] Read more.

Directed Energy Deposition (DED), a branch of AM processes, has emerged as a significant technique for fabricating large metal components in sectors such as aerospace, automotive, and healthcare. DED is characterized by its high deposition rate and scalability, which stand out among other AM processes. However, it encounters critical issues such as residual stresses, distortion, porosity, and rough surfaces resulting from rapid melting and solidification. As a novel advancement, Ultrasonic-Assisted Directed Energy Deposition (UA-DED) integrates ultrasonic oscillations into DED aimed at addressing these challenges. Herein, the latest research related to the UA-DED process and the current major challenges of the DED process, residual stresses, porosity, and crack defects are critically reviewed. Subsequently, the paper also details the working principle and system components of UA-DED technology and reviews the material improvement by introducing UA into the DED process, grain, porosity, tensile properties, and deposition defects. The most critical optimization methods of process parameter variables for UA and the different material interaction mechanisms between UA and DED processes are identified and discussed in detail. Finally, the perspectives on the research gap and potential future developments in UA-DED are also discussed. Full article

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16 pages, 6028 KiB

Open AccessEditor’s ChoiceArticle

Insights into the Spray Synthesis of UiO-66 and UiO-66-NH₂ Metal–Organic Frameworks: Effect of Zirconium Precursors and Process Parameters

by Masaru Kubo, Yusuke Miyoshi, Yushi Uchitomi and Manabu Shimada

Crystals 2024, 14(2), 116; https://doi.org/10.3390/cryst14020116 - 24 Jan 2024

Cited by 5 | Viewed by 3848

Abstract

UiO-66, a zirconium-based metal–organic framework, was synthesized using a one-step spray synthesis method to investigate the effects of preheating the precursor solution and Zr sources on crystallinity. Using ZrCl₄ with water as a modulator requires preheating at 80 °C for 120 min [...] Read more.

UiO-66, a zirconium-based metal–organic framework, was synthesized using a one-step spray synthesis method to investigate the effects of preheating the precursor solution and Zr sources on crystallinity. Using ZrCl₄ with water as a modulator requires preheating at 80 °C for 120 min or 120 °C for 30 min for the spray synthesis of UiO-66 to form secondary building units (SBUs). By contrast, the use of Zr(OnPr)₄ with acetic acid (AcOH) as a modulator allowed the spray synthesis of UiO-66 and UiO-66-NH₂ without preheating because of the rapid formation of SBUs with AcOH. The spray-synthesized UiO-66 using Zr(OnPr)₄ exhibited a BET surface area of 1258 m²/g and a CO₂ adsorption capacity of 3.43 mmol/g at 273 K and 1 bar, while UiO-66-NH₂ exhibited a BET surface area of 1263 m²/g and a CO₂ adsorption capacity of 6.11 mmol/g under the same conditions. Full article

(This article belongs to the Section Hybrid and Composite Crystalline Materials)

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16 pages, 7643 KiB

Open AccessEditor’s ChoiceArticle

Combustion Synthesis of Zirconium-Doped Ceria Nanocatalyst

by Katarina Mužina, Stanislav Kurajica, Helena Bach-Rojecky, Filip Brleković and Marina Duplančić

Crystals 2024, 14(2), 108; https://doi.org/10.3390/cryst14020108 - 23 Jan 2024

Cited by 1 | Viewed by 2433

Abstract

Zirconium-doped ceria is a promising and extensively researched catalytic material with notable use in three-way catalytic converters, the oxidation of volatile organic compounds and solid oxide fuel cells. In this work, pure and zirconium-doped ceria nanoparticles (Ce_1−xZr_xO₂, [...] Read more.

Zirconium-doped ceria is a promising and extensively researched catalytic material with notable use in three-way catalytic converters, the oxidation of volatile organic compounds and solid oxide fuel cells. In this work, pure and zirconium-doped ceria nanoparticles (Ce_1−xZr_xO₂, where x = 0, 0.1, 0.2, and 0.3) were prepared by combustion synthesis using glycine as the fuel and cerium and zirconium nitrate as oxidants. The obtained powders were characterized using X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, differential thermal and thermogravimetric analysis, UV–Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The combustion temperature increases with the increase in zirconium content in the samples, but the XRD patterns exclusively show ceria diffraction peaks. The crystallite sizes are in the range from 25.2 to 11.7 nm, and do not vary substantially after thermal treatment, indicating the good thermal stability of the prepared nanocatalysts. XPS analysis showed that the surface amount of zirconium is lower than the nominal and that the ceria sample with 10 mol. % of zirconium has a higher amount of oxygen vacancies than the 30 mol. % Zr-doped sample. The 10 mol. % Zr-doped sample displays the best catalytic activity in the BTEX (benzene, toluene, ethylbenzene, and o-xylene) oxidation process. Full article

(This article belongs to the Special Issue Metal Oxides: Crystal Structure, Synthesis and Characterization)

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26 pages, 4510 KiB

Open AccessEditor’s ChoiceReview

Crystal Engineering of Hydrogen Bonding for Direct Air Capture of CO₂: A Quantum Crystallography Perspective

by Sylwia Pawlędzio and Xiaoping Wang

Crystals 2024, 14(1), 77; https://doi.org/10.3390/cryst14010077 - 13 Jan 2024

Cited by 5 | Viewed by 3290

Abstract

Rising atmospheric CO₂ levels demand efficient and sustainable carbon capture solutions. Direct air capture (DAC) via crystallizing hydrogen-bonded frameworks such as carbonate salts has emerged as a promising approach. This review explores the potential of crystal engineering, in tandem with advanced quantum [...] Read more.

Rising atmospheric CO₂ levels demand efficient and sustainable carbon capture solutions. Direct air capture (DAC) via crystallizing hydrogen-bonded frameworks such as carbonate salts has emerged as a promising approach. This review explores the potential of crystal engineering, in tandem with advanced quantum crystallography techniques and computational modeling, to unlock the full potential of DAC materials. We examine the critical role of hydrogen bonding and other noncovalent interactions within a family of bis-guanidines that governs the formation of carbonate salts with high CO₂ capture capacity and low regeneration energies for utilization. Quantum crystallography and charge density analysis prove instrumental in elucidating these interactions. A case study of a highly insoluble carbonate salt of a 2,6-pyridine-bis-(iminoguanidine) exemplifies the effectiveness of these approaches. However, challenges remain in the systematic and precise determination of hydrogen atom positions and atomic displacement parameters within DAC materials using quantum crystallography, and limitations persist in the accuracy of current energy estimation models for hydrogen bonding interactions. Future directions lie in exploring diverse functional groups, designing advanced hydrogen-bonded frameworks, and seamlessly integrating experimental and computational modeling with machine learning. This synergistic approach promises to propel the design and optimization of DAC materials, paving the way for a more sustainable future. Full article

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11 pages, 3171 KiB

Open AccessEditor’s ChoiceArticle

Segregation of Phosphorus and Silicon at the Grain Boundary in Bcc Iron via Machine-Learned Force Fields

by Miroslav Černý and Petr Šesták

Crystals 2024, 14(1), 74; https://doi.org/10.3390/cryst14010074 - 12 Jan 2024

Cited by 2 | Viewed by 1651

Abstract

The study of the effects of impurity on grain boundaries is a critical aspect of materials science, particularly when it comes to understanding and controlling the properties of materials for specific applications. One of the related key issues is the segregation preference of [...] Read more.

The study of the effects of impurity on grain boundaries is a critical aspect of materials science, particularly when it comes to understanding and controlling the properties of materials for specific applications. One of the related key issues is the segregation preference of impurity atoms in the grain boundary region. In this paper, we employed the on-the-fly machine learning to generate force fields, which were subsequently used to calculate the segregation energies of phosphorus and silicon in bcc iron containing the ∑5(310)[001] grain boundary. The generated force fields were successfully benchmarked using ab initio data. Our further calculations considered impurity atoms at a number of possible interstitial and substitutional segregation sites. Our predictions of the preferred sites agree with the experimental observations. Planar concentration of impurity atoms affects the segregation energy and, moreover, can change the preferred segregation sites. Full article

(This article belongs to the Section Crystalline Metals and Alloys)

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9 pages, 2237 KiB

Open AccessEditor’s ChoiceArticle

The Solid-Phase Transition of Carbapenem CS-023 Polymorphs and the Change in Helicity Observed in the Transition

by Shinji Matsuura, Koichi Igarashi, Masayuki Azuma and Hiroshi Ooshima

Crystals 2024, 14(1), 71; https://doi.org/10.3390/cryst14010071 - 11 Jan 2024

Cited by 1 | Viewed by 1312

Abstract

Anti-solvent crystallization of carbapenem CS-023 was performed at 25 °C. The following results were obtained: (1) A solvate crystal, Form A (5/2 Ethanol·1/2 H₂O), was recovered from 80 v/v% ethanol solution; (2) Form A transformed to Form H [...] Read more.

Anti-solvent crystallization of carbapenem CS-023 was performed at 25 °C. The following results were obtained: (1) A solvate crystal, Form A (5/2 Ethanol·1/2 H₂O), was recovered from 80 v/v% ethanol solution; (2) Form A transformed to Form H (4H₂O) through solid-phase transition through the solvate-free polymorph, Form A-2, and Form A also transformed into Form C (1Ethanol·3H₂O) through solvent-mediated transformation. In the present study, we found that Form C also transforms to Form H through the solid-phase transition through the solvate-free polymorph Form C-2. The three polymorphs, Forms A, H, and C, were composed of helical chain structures. However, there was an incomprehensible affair in the solid-phase transition among the three polymorphs. Namely, Form A comprised a left-handed helix. On the other hand, Form C’s and Form H’s helix chains were in a left- and right-handed helix complex, respectively. The solid-phase transition of Form A into Form H suggested a switch in helicity in the solid. We attempted to explain the helicity change in the solid-phase transition. As a result, we suggest that the over-absorption of water by Form A-2 at high humidity plays a vital role in the helicity change. Full article

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12 pages, 3041 KiB

Open AccessEditor’s ChoiceArticle

Monitoring of Carbonated Hydroxyapatite Growth on Modified Polycrystalline CVD-Diamond Coatings on Titanium Substrates

by Rocco Carcione, Valeria Guglielmotti, Francesco Mura, Silvia Orlanducci and Emanuela Tamburri

Crystals 2024, 14(1), 66; https://doi.org/10.3390/cryst14010066 - 6 Jan 2024

Cited by 2 | Viewed by 2030

Abstract

Production of diamond coatings on titanium substrates has demonstrated as a promising strategy for applications ranging from biosensing to hard tissue engineering. The present study focuses on monitoring the nucleation and growth of bone-like carbonated-hydroxyapatite (C-HA) on polycrystalline diamond (PCD) synthetized on titanium [...] Read more.

Production of diamond coatings on titanium substrates has demonstrated as a promising strategy for applications ranging from biosensing to hard tissue engineering. The present study focuses on monitoring the nucleation and growth of bone-like carbonated-hydroxyapatite (C-HA) on polycrystalline diamond (PCD) synthetized on titanium substrate by means of a hot filament chemical vapor deposition (HF-CVD) method. The surface terminations of diamond coatings were selectively modified by oxidative treatments. The process of the C-HA deposition, accomplished by precipitation from simulated body fluid (SBF), was monitored from 3 to 20 days by Raman spectroscopy analysis. The coupling of morphological and structural investigations suggests that the modulation of the PCD surface chemistry enhances the bioactivity of the produced materials, allowing for the formation of continuous C-HA coatings with needle-like texture and chemical composition typical of those of the bone mineral. Specifically, after 20 days of immersion in SBF the calculated carbonate weight percent and the Ca/P ratio are 5.5% and 2.1, respectively. Based on these results, this study brings a novelty in tailoring the CVD-diamond properties for advanced biomedical and technological applications. Full article

(This article belongs to the Special Issue Poly-Crystalline/Single-Crystalline Diamonds)

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19 pages, 10482 KiB

Open AccessEditor’s ChoiceArticle

Transferring Crystallization Conditions from Small to Larger Scale for Achieving Targeted Crystal Morphologies of an Active Pharmaceutical Ingredient

by Nicolás Antonio Ramos Ojeda and Matthias Kind

Crystals 2024, 14(1), 42; https://doi.org/10.3390/cryst14010042 - 28 Dec 2023

Cited by 3 | Viewed by 2450

Abstract

Crystal morphology plays a critical role in the processability and physicochemical behavior of active pharmaceutical ingredients. Manipulating crystal morphology involves consideration of crystallization conditions such as temperature, supersaturation, and solvent choice. Typically, experimental screenings on a small scale are conducted to find targeted [...] Read more.

Crystal morphology plays a critical role in the processability and physicochemical behavior of active pharmaceutical ingredients. Manipulating crystal morphology involves consideration of crystallization conditions such as temperature, supersaturation, and solvent choice. Typically, experimental screenings on a small scale are conducted to find targeted crystal morphologies. However, results from such small-scale experiments do not assure direct success at a larger scale, particularly if the small-scale setup differs significantly from a conventional stirred crystallizator. In this study, we successfully validated the morphologies observed in the small-scale experiments of an exemplary API, Bitopertin, when scaled up by a factor of 200, through the maintenance of identical process conditions and geometrical vessel relations. This successful scalability highlights the significant potential of small-scale crystallization studies to provide a reliable foundation for further exploration in large-scale endeavors. Full article

(This article belongs to the Section Crystal Engineering)

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11 pages, 884 KiB

Open AccessEditor’s ChoiceArticle

One-Dimensional Gap Soliton Molecules and Clusters in Optical Lattice-Trapped Coherently Atomic Ensembles via Electromagnetically Induced Transparency

by Zhiming Chen, Hongqiang Xie, Qi Zhou and Jianhua Zeng

Crystals 2024, 14(1), 36; https://doi.org/10.3390/cryst14010036 - 27 Dec 2023

Viewed by 1468

Abstract

In past years, optical lattices have been demonstrated as an excellent platform for making, understanding, and controlling quantum matters at nonlinear and fundamental quantum levels. Shrinking experimental observations include matter-wave gap solitons created in ultracold quantum degenerate gases, such as Bose–Einstein condensates with [...] Read more.

In past years, optical lattices have been demonstrated as an excellent platform for making, understanding, and controlling quantum matters at nonlinear and fundamental quantum levels. Shrinking experimental observations include matter-wave gap solitons created in ultracold quantum degenerate gases, such as Bose–Einstein condensates with repulsive interaction. In this paper, we theoretically and numerically study the formation of one-dimensional gap soliton molecules and clusters in ultracold coherent atom ensembles under electromagnetically induced transparency conditions and trapped by an optical lattice. In numerics, both linear stability analysis and direct perturbed simulations are combined to identify the stability and instability of the localized gap modes, stressing the wide stability region within the first finite gap. The results predicted here may be confirmed in ultracold atom experiments, providing detailed insight into the higher-order localized gap modes of ultracold bosonic atoms under the quantum coherent effect called electromagnetically induced transparency. Full article

(This article belongs to the Topic Mathematical Applications of Nonlinear Wave Properties in Crystalline and Dispersive Media)

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13 pages, 1940 KiB

Open AccessEditor’s ChoiceArticle

Study on the Growth and Regulation of Large-Particle Sr(OH)₂·8H₂O Crystals with Process Analytical Technology

by Binbin Shi, Yongjuan Zhang, Shudong Liang, Yanan Wang, Yan Jing, Xingwu Zou and Xuezhong Wang

Crystals 2024, 14(1), 4; https://doi.org/10.3390/cryst14010004 - 20 Dec 2023

Viewed by 1655

Abstract

Sr(OH)₂ is an indispensable strontium compound extensively harnessed in sugar refining, strontium lubricating wax formulation, and polymer plastic stabilization. Sr(OH)₂·8H₂O is the prevalent hydrate form of Sr(OH)₂. Deprived of moisture via vacuum drying, Sr(OH)₂ can [...] Read more.

Sr(OH)₂ is an indispensable strontium compound extensively harnessed in sugar refining, strontium lubricating wax formulation, and polymer plastic stabilization. Sr(OH)₂·8H₂O is the prevalent hydrate form of Sr(OH)₂. Deprived of moisture via vacuum drying, Sr(OH)₂ can be procured from Sr(OH)₂·8H₂O. Sr(OH)₂·8H₂O particles with larger sizes exhibit impressive attributes such as facile solid–liquid divergence, elevated product purity, expedient drying, and resilience to agglomeration, which have garnered significant interest. Given the superior quality of the product and the dependability of the process, process analytical technology (PAT) has been extensively employed in the pharmaceutical sector, rendering it feasible to employ PAT to fabricate large-particle Sr(OH)₂·8H₂O crystals. This study utilizes industrial SrCO₃ to prepare high-purity Sr(OH)₂·8H₂O with a purity of over 99.5%. The growth process of single crystals was observed using a hot-stage microscope, and the growth process of large-particle Sr(OH)₂·8H₂O was optimized and regulated online using PAT. The optimal process conditions were optimized, and large-particle Sr(OH)₂·8H₂O crystals were obtained by adding crystal seeds. On this basis, we proposed a seed control mechanism for Sr(OH)₂·8H₂O. Full article

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15 pages, 6390 KiB

Open AccessEditor’s ChoiceArticle

Sol–Gel Synthesis of ZnO:Li Thin Films: Impact of Annealing on Structural and Optical Properties

by Tatyana Ivanova, Antoaneta Harizanova, Tatyana Koutzarova, Benedicte Vertruyen and Raphael Closset

Crystals 2024, 14(1), 6; https://doi.org/10.3390/cryst14010006 - 20 Dec 2023

Cited by 5 | Viewed by 2569

Abstract

A sol–gel deposition approach was applied for obtaining nanostructured Li-doped ZnO thin films. ZnO:Li films were successfully spin-coated on quartz and silicon substrates. The evolution of their structural, vibrational, and optical properties with annealing temperature (300–600 °C) was studied by X-ray diffraction (XRD), [...] Read more.

A sol–gel deposition approach was applied for obtaining nanostructured Li-doped ZnO thin films. ZnO:Li films were successfully spin-coated on quartz and silicon substrates. The evolution of their structural, vibrational, and optical properties with annealing temperature (300–600 °C) was studied by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV-VIS spectroscopic, and field emission scanning electron microscopic (FESEM) characterization techniques. It was found that lithium doping maintains the wurtzite arrangement of ZnO, with increasing crystallite sizes when increasing the annealing temperature. Analysis of the FTIR spectra revealed a broad main absorption band (around 404 cm⁻¹) for Li-doped films, implying the inclusion of Li into the ZnO lattice. The ZnO:Li films were transparent, with slightly decreased transmittance after the use of higher annealing temperatures. The porous network of undoped ZnO films was transformed to a denser, grained, packed structure, induced by lithium doping. Full article

(This article belongs to the Special Issue Advances in Synthesis, Characterization, and Application of Thin Films)

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11 pages, 8281 KiB

Open AccessEditor’s ChoiceArticle

Structural and Electrochemical Properties of F-Doped RbTiOPO₄ (RTP:F) Predicted from First Principles

by Adriana Bocchini, Yingjie Xie, Wolf Gero Schmidt and Uwe Gerstmann

Crystals 2024, 14(1), 5; https://doi.org/10.3390/cryst14010005 - 20 Dec 2023

Cited by 1 | Viewed by 1514

Abstract

Batteries based on heavier alkali ions are considered promising candidates to substitute for current Li-based technologies. In this theoretical study, we characterize the structural properties of a novel material, i.e., F-doped RbTiOPO

_{4}

(RbTiPO

_{4}

F, RTP:F), and discuss aspects of its electrochemical [...] Read more.

Batteries based on heavier alkali ions are considered promising candidates to substitute for current Li-based technologies. In this theoretical study, we characterize the structural properties of a novel material, i.e., F-doped RbTiOPO

_{4}

(RbTiPO

_{4}

F, RTP:F), and discuss aspects of its electrochemical performance in Rb-ion batteries (RIBs) using density functional theory (DFT). According to our calculations, RTP:F is expected to retain the so-called KTiOPO

_{4}

(KTP)-type structure, with lattice parameters of

13.236

Å,

6.616

Å, and

10.945

Å. Due to the doping with F, the crystal features eight extra electrons per unit cell, whereby each of these electrons is trapped by one of the surrounding Ti atoms in the cell. Notably, the ground state of the system corresponds to a ferromagnetic spin configuration (i.e.,

S = 4

). The deintercalation of Rb leads to the oxidation of the Ti atoms in the cell (i.e., from Ti

^{3 +}

to Ti

^{4 +}

) and to reduced magnetic moments. The material promises interesting electrochemical properties for the cathode: rather high average voltages above

2.8

V and modest volume shrinkages below 13% even in the fully deintercalated case are predicted. Full article

(This article belongs to the Special Issue New Materials for Electrochemical Energy Storage Systems and Catalysis)

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15 pages, 5055 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Impact of Structural Strain in Perovskite Epitaxial Thin Films on Their Functional Properties

by Florin Andrei, Maria Dinescu, Valentin Ion, Floriana Craciun, Ruxandra Birjega and Nicu Doinel Scarisoreanu

Crystals 2023, 13(12), 1686; https://doi.org/10.3390/cryst13121686 - 14 Dec 2023

Cited by 2 | Viewed by 2220

Abstract

The strain engineering effects induced by different means, e.g., the substrate lattice mismatch and/or chemical doping, on the functional properties of perovskite thin films have triggered interest in the use of these materials in different applications such as energy storage/generation or photonics. The [...] Read more.

The strain engineering effects induced by different means, e.g., the substrate lattice mismatch and/or chemical doping, on the functional properties of perovskite thin films have triggered interest in the use of these materials in different applications such as energy storage/generation or photonics. The effects of the film’s thickness and strain state of the structure for the lead-free perovskite ferrite-based materials (BiFeO₃-BFO; Y-doped BiFeO₃-BYFO; LaFeO₃-LFO) on their functional properties are highlighted here. As was previously demonstrated, the dielectric properties of BFO epitaxial thin films are strongly affected by the film thickness and by the epitaxial strain induced by the lattice mismatch between substrate and film. Doping the BiFeO₃ ferroelectric perovskite with rare-earth elements or inducing a high level of structural deformation into the crystalline structure of LaFeO₃ thin films have allowed the tuning of functional properties of these materials, such as dielectric, optical or photocatalytic ones. These changes are presented in relation to the appearance of complex ensembles of nanoscale phase/nanodomains within the epitaxial films due to strain engineering. However, it is a challenge to maintain the same level of epitaxial strain present in ultrathin films (<10 nm) and to preserve or tune the positive effects in films of thicknesses usually higher than 30 nm. Full article

(This article belongs to the Special Issue Ferroelectric Materials)

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12 pages, 7096 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Structural Characterization of Layered Ni^+1/+2 Oxides Obtained by Topotactic Oxygen Release on Nd_2−xSr_xNiO_4−δ Single Crystals

by Chavana Hareesh, Monica Ceretti, Philippe Papet, Alexeï Bosak, Martin Meven and Werner Paulus

Crystals 2023, 13(12), 1670; https://doi.org/10.3390/cryst13121670 - 9 Dec 2023

Cited by 1 | Viewed by 1893

Abstract

Layered nickelate oxides containing Ni¹⁺/Ni²⁺ are isoelectronic to Cu²⁺/Cu³⁺ compounds and of present interest with respect to recent findings of superconductivity in a series of different compositions. It is thereby questionable why superconductivity is still rare to [...] Read more.

Layered nickelate oxides containing Ni¹⁺/Ni²⁺ are isoelectronic to Cu²⁺/Cu³⁺ compounds and of present interest with respect to recent findings of superconductivity in a series of different compositions. It is thereby questionable why superconductivity is still rare to find in nickelates, compared to the much larger amount of superconducting cuprates. Anisotropic d_z² vs. d_x²−y² orbital occupation as well as interface-induced superconductivity are two of the main advanced arguments. We are here interested in investigating the feasibility of synthesizing layered nickelate-type oxides, where the Ni¹⁺/Ni²⁺ ratio can be tuned by oxygen and/or cation doping. Our strategy is to synthesize Sr-doped n = 1 Ruddlesden–Popper type Nd_2−xSr_xNiO_4+δ single crystals, which are then reduced by H₂ gas, forming Nd_2−xSr_xNiO_4−δ via a topotactic oxygen release at moderate temperatures. We report here on structural studies carried out on single crystals by laboratory and synchrotron diffraction using pixel detectors. We evidence the general possibility to obtain reduced single crystals despite their increased orthorhombicity. This must be regarded as a milestone to obtain single crystalline nickelate oxides, which further on contain charge-ordering of Ni¹⁺/Ni²⁺, opening the access towards anisotropic properties. Full article

(This article belongs to the Special Issue High Temperature Superconductor)

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13 pages, 3179 KiB

Open AccessEditor’s ChoiceArticle

O-Vacancy-Rich ε-MnO₂ Synthesized at Hydrophobic Interface: An Efficient Fenton-like Catalyst for Removing Ciprofloxacin from Water

by Yulong Chen, Yuan Chi, Xiao Wu, Cong Lin, Tengfei Lin, Min Gao, Chunlin Zhao and Baisheng Sa

Crystals 2023, 13(12), 1664; https://doi.org/10.3390/cryst13121664 - 6 Dec 2023

Viewed by 1603

Abstract

The widespread use of pharmaceuticals and personal care products (PPCPs) in many fields has brought convenience to human lives but has also caused unavoidable environmental pollution issues. In particular, the resistance gene problem resulting from accumulating antibiotics that cannot be fully absorbed by [...] Read more.

The widespread use of pharmaceuticals and personal care products (PPCPs) in many fields has brought convenience to human lives but has also caused unavoidable environmental pollution issues. In particular, the resistance gene problem resulting from accumulating antibiotics that cannot be fully absorbed by biological individuals has been a concern; thus, it is urgent to find efficient technologies to boost the degradation efficiency of antibiotics in the environment. Here, an ε-MnO₂ catalyst was prepared by a novel droplet-interface-drying method and utilized as a Fenton-like catalyst for efficiently degrading ciprofloxacin (CIP). The ε-MnO₂ shell was formed preferentially at the gas–liquid interface and then continued to decompose into ε-MnO₂ with abundant O vacancies in the air-insulated microcavity. The XPS result confirms that this particular preparation method can regulate the content of O vacancies in the material. Compared with ε-MnO₂ samples obtained by the direct drying method (ε-MnO₂-B), the catalytic performance of ε-MnO₂ prepared by the droplet-interface-drying method (ε-MnO₂-P) is significantly improved. By activating peroxymonosulfate (PMS) with the ε-MnO₂-P catalyst, the CIP degradation efficiency can reach 84.1%. The detection and analysis of reactive oxygen species (ROS) in the ε-MnO₂-P/PMS oxidation system confirms that ·OH, SO₄^·− and ¹O₂ are the main ROS for CIP degradation. This study highlights the creation of miniature hypoxic space to regulate the content of O vacancies in ε-MnO₂, providing a new idea for the synthesis of other O-vacancy-rich materials. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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10 pages, 2827 KiB

Open AccessEditor’s ChoiceArticle

Wafer-Scale Emission Energy Modulation of Indium Flushed Quantum Dots

by Nikolai Spitzer, Nikolai Bart, Hans-Georg Babin, Marcel Schmidt, Andreas D. Wieck and Arne Ludwig

Crystals 2023, 13(12), 1657; https://doi.org/10.3390/cryst13121657 - 30 Nov 2023

Cited by 1 | Viewed by 1529

Abstract

Semiconductor self-assembled quantum dots (QDs) have garnered immense attention for their potential in various quantum technologies and photonics applications. Here, we explore a novel approach for fine-tuning the emission wavelength of QDs by building upon the indium flush growth method: Submonolayer variations in [...] Read more.

Semiconductor self-assembled quantum dots (QDs) have garnered immense attention for their potential in various quantum technologies and photonics applications. Here, we explore a novel approach for fine-tuning the emission wavelength of QDs by building upon the indium flush growth method: Submonolayer variations in the capping thickness reveal a non-monotonic progression, where the emission energy can decrease even though the capping thickness decreases. indium flush, a well-known technique for inducing blue shifts in quantum dot emissions, involves the partial capping of QDs with GaAs followed by a temperature ramp-up. However, our findings reveal that the capping layer roughness, stemming from fractional monolayers during overgrowth, plays a pivotal role in modulating the emission energy of these QDs. We propose increased indium interdiffusion between the QDs and the surrounding GaAs capping layer for a rough surface surrounding the QD as the driving mechanism. This interdiffusion alters the indium content within the QDs, resulting in an additional emission energy shift, counterintuitive to the capping layer’s thickness increase. We utilize photoluminescence spectroscopy to generate wafer maps depicting the emission spectrum of the QDs. Using thickness gradients, we produce systematic variations in the capping layer thickness on 3″ wafers, resulting in modulations of the emission energy of up to 26 meV. Full article

(This article belongs to the Special Issue Modelling of Crystal Growth Processes)

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11 pages, 3200 KiB

Open AccessEditor’s ChoiceArticle

In Situ Growth of Mg-Fe Layered Double Hydroxides (LDH) Film on Titanium Dental Implant Substrates for pH Regulation in Oral Environments

by Yuliu Li, Francesco Gianfreda, Carlotta Danesi, Patrizio Bollero, Anita Ermini, Roberto Pizzoferrato and Eleonora Nicolai

Crystals 2023, 13(12), 1636; https://doi.org/10.3390/cryst13121636 - 26 Nov 2023

Cited by 1 | Viewed by 1678

Abstract

Layered double hydroxides (LDHs) consist of two-dimensional, positively charged lamellar structures with the ability to host various anions in the interlayer spaces, which grants them unique properties and tunable characteristics. LDHs, a class of versatile inorganic compounds, have recently emerged as promising candidates [...] Read more.

Layered double hydroxides (LDHs) consist of two-dimensional, positively charged lamellar structures with the ability to host various anions in the interlayer spaces, which grants them unique properties and tunable characteristics. LDHs, a class of versatile inorganic compounds, have recently emerged as promising candidates for enhancing osseointegration. A suitable alkaline microenvironment is thought to be beneficial for stimulating osteoblasts’ differentiation (responsible for bone matrix formation) while suppressing osteoclast generation (responsible for bone matrix disintegration). LDHs are prone to adjusting their alkalinity and thus offering us the chance to study how pH affects cellular behavior. LDHs can indeed modulate the local pH, inflammatory responses, and oxidative stress levels, factors that profoundly influence the behavior of osteogenic cells and their interactions with the implant surface. Herein, we deposited Mg–Fe LDH films on titanium substrates for dental implants. The modified Ti substrates was more alkaline in comparison to the bare ones, with a pH higher than 8 after hydrolysis in an aqueous environment. Full article

(This article belongs to the Special Issue Advanced Surface Engineering Materials: Characterization and Properties)

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13 pages, 3248 KiB

Open AccessEditor’s ChoiceArticle

NiO/Ga₂O₃ Vertical Rectifiers of 7 kV and 1 mm² with 5.5 A Forward Conduction Current

by Jian-Sian Li, Hsiao-Hsuan Wan, Chao-Ching Chiang, Timothy Jinsoo Yoo, Fan Ren, Honggyu Kim and Stephen J. Pearton

Crystals 2023, 13(12), 1624; https://doi.org/10.3390/cryst13121624 - 23 Nov 2023

Cited by 6 | Viewed by 2357

Abstract

In this study, we present the fabrication and characterization of vertically oriented NiO/β polymorph n-Ga₂O₃/n+ Ga₂O₃ heterojunction rectifiers featuring a substantial area of 1 mm². A dual-layer SiN_X/SiO₂ dielectric field plate [...] Read more.

In this study, we present the fabrication and characterization of vertically oriented NiO/β polymorph n-Ga₂O₃/n+ Ga₂O₃ heterojunction rectifiers featuring a substantial area of 1 mm². A dual-layer SiN_X/SiO₂ dielectric field plate edge termination was employed to increase the breakdown voltage (V_B). These heterojunction rectifiers exhibit remarkable simultaneous achievement of high breakdown voltage and substantial conducting currents. In particular, the devices manifest V_B of 7 kV when employing a 15 µm thick drift layer doping concentration of 8.8 × 10¹⁵ cm⁻³, concurrently demonstrating a forward current of 5.5 A. The thick drift layer is crucial in obtaining high V_B since similar devices fabricated on 10 µm thick epilayers had breakdown voltages in the range of 3.6–4.0 kV. Reference devices fabricated on the 15 µm drift layers had V_B of 5 kV. The breakdown is still due to leakage current from tunneling and thermionic emission and not from avalanche breakdown. An evaluation of the power figure-of-merit, represented by V_B²/R_ON, reveals a value of 9.2 GW·cm⁻², where R_ON denotes the on-state resistance, measuring 5.4 mΩ·cm². The Coff was 4 nF/cm², leading to an R_ON × C_off of 34 ps and F_CO of 29 GHz. The turn-on voltage for these rectifiers was ~2 V. This exceptional performance surpasses the theoretical unipolar one-dimensional (1D) limit of both SiC and GaN, underscoring the potential of β-Ga₂O₃ for forthcoming generations of high-power rectification devices. Full article

(This article belongs to the Special Issue Wide-Bandgap Semiconductor Materials, Devices and Systems)

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28 pages, 5270 KiB

Open AccessEditor’s ChoiceReview

Liquid Crystals for Luminescent Concentrators: A Review

by Atchutananda Surampudi, Guanxiong Zhang, Ravinder Singh, Grahame Faulkner, Dominic C. O’Brien, Martin J. Booth and Stephen M. Morris

Crystals 2023, 13(12), 1615; https://doi.org/10.3390/cryst13121615 - 22 Nov 2023

Cited by 7 | Viewed by 3067

Abstract

Luminescent optical concentrators are thin films containing fluorescent dyes that enable light collection over a wide field of view without the need to track the path of the Sun. However, a disadvantage when using luminescent concentrators is that the performance is often impeded [...] Read more.

Luminescent optical concentrators are thin films containing fluorescent dyes that enable light collection over a wide field of view without the need to track the path of the Sun. However, a disadvantage when using luminescent concentrators is that the performance is often impeded by surface losses through these films. Liquid-crystal (LC) hosts are attractive for luminescent concentrators, as they impart, at the very least, an orientational ordering to the transition dipole moment of the dyes dispersed within these films. This enables the directivity of both the absorption and emission and can reduce surface losses by, for example, adopting the homeotropic alignment of the LC director. This article reviews the developments and applications of LCs to luminescent optical concentrators and describes the strategies that have been introduced to further combat losses by decoupling the absorption and emission processes through Förster energy transfer, the approaches employed to enhance the chemical structures of the dyes, and the methods of using alternative LC phases and external configurations. The review presents a comprehensive summary of the material combinations and the techniques that have been considered in the development of LC-based concentrator films and concludes with a discussion about the future perspectives for these exciting optical concentrators. Full article

(This article belongs to the Special Issue Reviews in Liquid Crystals)

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15 pages, 18962 KiB

Open AccessEditor’s ChoiceArticle

Wetting of Graphite and Platinum Substrate by Oxide System with Graded B₂O₃ Content

by Dalibor Novák, Lenka Řeháčková, Vlastimil Novák, Dalibor Matýsek and Pavlína Peikertová

Crystals 2023, 13(12), 1618; https://doi.org/10.3390/cryst13121618 - 22 Nov 2023

Cited by 2 | Viewed by 1366

Abstract

This work focuses on wetting two types of substrates (a platinum substrate and a polished graphite substrate) by molten polycomponent oxide system CaO–MgO–SiO₂–Al₂O₃–B₂O₃ to test the level of interaction at high temperatures. The tested [...] Read more.

This work focuses on wetting two types of substrates (a platinum substrate and a polished graphite substrate) by molten polycomponent oxide system CaO–MgO–SiO₂–Al₂O₃–B₂O₃ to test the level of interaction at high temperatures. The tested systems were subjected to high-temperature wetting tests in the temperature range from liquidus temperature to 1550 °C using the sessile drop method. A total of four oxide systems were tested with graded boron oxide contents ranging from 0 to 30 wt%. The experiments were conducted in a CLASIC high-temperature resistance observation furnace and an inert atmosphere of high-purity argon. Droplet silhouettes were obtained with a CANON EOS 550D high-resolution camera during heat treatment, with reactive and non-reactive wetting occurring depending on the substrate type. The dependence of the average wetting angles on temperature and time was evaluated, and it was found that boron oxide decreased the average wetting angles of molten oxide droplets. The analyses were accompanied by the SEM/EDX analysis of the substrate and FTIR analysis of the droplets after high-temperature experiments. The phase composition of the oxide systems was evaluated by XRD analysis. Full article

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11 pages, 1753 KiB

Open AccessEditor’s ChoiceArticle

Optimization of a LaNiO₃ Bottom Electrode for Flexible Pb(Zr,Ti)O₃ Film-Based Ferroelectric Random Access Memory Applications

by Yeong Uk Choi, Hyun Soo Ahn, Jung Ehy Hong, Dong In Yang, Hwa-Pyeong Lee, Dae-Yong Jeong, Minbaek Lee, Jong Hun Kim and Jong Hoon Jung

Crystals 2023, 13(12), 1613; https://doi.org/10.3390/cryst13121613 - 21 Nov 2023

Cited by 1 | Viewed by 2197

Abstract

The direct growth of ferroelectric films onto flexible substrates has garnered significant interest in the advancement of portable and wearable electronic devices. However, the search for an optimized bottom electrode that can provide a large and stable remnant polarization is still ongoing. In [...] Read more.

The direct growth of ferroelectric films onto flexible substrates has garnered significant interest in the advancement of portable and wearable electronic devices. However, the search for an optimized bottom electrode that can provide a large and stable remnant polarization is still ongoing. In this study, we report the optimization of an oxide-based LaNiO₃ (LNO) electrode for high-quality Pb(Zr_0.52Ti_0.48)O₃ (PZT) thick films. The surface morphology and electrical conductivity of sol-gel-grown LNO films on a fluorophlogopite mica (F-mica) substrate were optimized at a crystallization temperature of 800 °C and a film thickness of 120 nm. Our approach represents the promising potential pairing between PZT and LNO electrodes. While LNO-coated F-mica maintains stable electrical conductivity during 1.0%-strain and 10⁴-bending cycles, the upper PZT films exhibit a nearly square-like polarization–electric field behavior under those stress conditions. After 10⁴ cycles at 0.5% strain, the remnant polarization shows decreases as small as ~14%. Under flat (bent) conditions, the value decreases to just 81% (49%) after 10¹⁰ fatigue cycles and to 96% (85%) after 10⁵ s of a retention test, respectively. Full article

(This article belongs to the Special Issue Ferroelectric and Multiferroic Thin Films)

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23 pages, 9437 KiB

Open AccessEditor’s ChoiceArticle

Additive Manufacturing and Mechanical Properties of Auxetic and Non-Auxetic Ti₂₄Nb₄Zr₈Sn Biomedical Stents: A Combined Experimental and Computational Modelling Approach

by Sudipta Pramanik, Dennis Milaege, Maxwell Hein, Kay-Peter Hoyer and Mirko Schaper

Crystals 2023, 13(11), 1592; https://doi.org/10.3390/cryst13111592 - 17 Nov 2023

Cited by 3 | Viewed by 2195

Abstract

The effect of plaque deposition (atherosclerosis) on blood flow behaviour is investigated via computational fluid dynamics and structural mechanics simulations. To mitigate the narrowing of coronary artery atherosclerosis (stenosis), the computational modelling of auxetic and non-auxetic stents was performed in this study to [...] Read more.

The effect of plaque deposition (atherosclerosis) on blood flow behaviour is investigated via computational fluid dynamics and structural mechanics simulations. To mitigate the narrowing of coronary artery atherosclerosis (stenosis), the computational modelling of auxetic and non-auxetic stents was performed in this study to minimise or even avoid these deposition agents in the future. Computational modelling was performed in unrestricted (open) conditions and restricted (in an artery) conditions. Finally, stent designs were produced by additive manufacturing, and mechanical testing of the stents was undertaken. Auxetic stent 1 and auxetic stent 2 exhibit very little foreshortening and radial recoil in unrestricted deployment conditions compared to non-auxetic stent 3. However, stent 2 shows structural instability (strut failure) during unrestricted deployment conditions. For the restricted deployment condition, stent 1 shows a higher radial recoil compared to stent 3. In the tensile test simulations, short elongation for stent 1 due to strut failure is demonstrated, whereas no structural instability is noticed for stent 2 and stent 3 until 0.5 (mm/mm) strain. The as-built samples show a significant thickening of the struts of the stents resulting in short elongations during tensile testing compared to the simulations (stent 2 and stent 3). A modelling framework for the stent deployment system that enables the selection of appropriate stent designs before in vivo testing is required. This leads to the acceleration of the development process and a reduction in time, resulting in less material wastage. The modelling framework shall be useful for doctors designing patient-specific stents. Full article

(This article belongs to the Special Issue New Materials and Concepts for Additive Manufacturing with Metals II)

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18 pages, 5329 KiB

Open AccessEditor’s ChoiceArticle

Growth, Structure, Spectroscopy, and Laser Operation of a “Mixed” Yb:(Y,Lu)₃Al₅O₁₂ Garnet Crystal

by Sami Slimi, Pavel Loiko, Mingyan Pan, Pauline Lehoux, Venkatesan Jambunathan, Martin Smrz, Tomas Mocek, Yicheng Wang, Weidong Chen, Valentin Petrov, Rosa Maria Solé, Magdalena Aguiló, Francesc Díaz, Patrice Camy and Xavier Mateos

Crystals 2023, 13(11), 1588; https://doi.org/10.3390/cryst13111588 - 15 Nov 2023

Cited by 4 | Viewed by 2043

Abstract

A single crystal of ytterbium-doped “mixed” yttrium–lutetium aluminum garnet with a stoichiometric composition of (Y_0.601Lu_0.233Yb_0.166)₃Al₅O₁₂ was grown by the Czochralski method and its structure, vibronic, spectroscopic, and laser properties were studied. The [...] Read more.

A single crystal of ytterbium-doped “mixed” yttrium–lutetium aluminum garnet with a stoichiometric composition of (Y_0.601Lu_0.233Yb_0.166)₃Al₅O₁₂ was grown by the Czochralski method and its structure, vibronic, spectroscopic, and laser properties were studied. The stimulated-emission cross-section for Yb³⁺ ions was maximized to 2.53 × 10⁻²⁰ cm² at 1031 nm. The emission bandwidth was ~8 nm, and the reabsorption-free luminescence lifetime of the ²F_5/2 state was 1.063 ms. Pumped at 941 nm, the Yb laser generated a maximum output power of 1.04 W at 1.03 and 1.05 μm with a high slope efficiency of 76.4% and a laser threshold of 76 mW. A continuous wavelength tuning over a range of 51.6 nm (1026.4–1078.0 nm) was also achieved. Power scaling was achieved using a 969 nm diode-pumped microchip cavity. A maximum output power of ~9 W was obtained at 1.05 μm with a slope efficiency of 76% and an almost circular laser beam profile. Full article

(This article belongs to the Special Issue Rare Earths-Doped Materials (3rd Edition))

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8 pages, 2227 KiB

Open AccessEditor’s ChoiceArticle

Innovative Method for the Mass Preparation of α″-Fe₁₆N₂ Powders via Gas Atomization

by Marian Grigoras, Mihaela Lostun, Marieta Porcescu, George Stoian, Gabriel Ababei and Nicoleta Lupu

Crystals 2023, 13(11), 1578; https://doi.org/10.3390/cryst13111578 - 9 Nov 2023

Cited by 3 | Viewed by 2694

Abstract

The iron nitride materials, especially α″-Fe₁₆N₂, are considered one of the most promising candidates for future rare-earth-free magnets. However, the mass production of α″-Fe₁₆N₂ powders as a raw material for permanent magnets is still challenging. In [...] Read more.

The iron nitride materials, especially α″-Fe₁₆N₂, are considered one of the most promising candidates for future rare-earth-free magnets. However, the mass production of α″-Fe₁₆N₂ powders as a raw material for permanent magnets is still challenging. In this work, starting from iron lumps as a raw material, we have managed to prepare the α″-Fe₁₆N₂ powders via the gas atomization method, followed by subsequent nitriding in an ammonia–hydrogen gas mixture stream. The particle size was controlled by changing the gas atomization preparation conditions. X-ray diffractograms (XRD) analyses show that the prepared powders are composed of α″-Fe₁₆N₂ and α-Fe phases. The α″-Fe₁₆N₂ volume ratio increases with decreasing powder size and increasing nitriding time, reaching a maximum of 57% α″-Fe₁₆N₂ phase in powders with size below 32 ± 3 μm after 96 h nitridation. The saturation magnetization reaches the value of 237 emu/g and a reasonable coercivity value of 884 Oe. Compared to the saturation magnetization values of α-Fe powders, the α″-Fe₁₆N₂ powders prepared through our proposed approach show an increase of up to 10% in saturation and demonstrate the possibility of mass production of α″-Fe₁₆N₂ powders as precursors of permanent magnets without rare earths. Full article

(This article belongs to the Special Issue Exploring the Magnetic World: Advances in Synthesis, Characterization, and Revolutionary Applications of Magnetic Nanoparticles)

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16 pages, 5574 KiB

Open AccessEditor’s ChoiceArticle

Single-Crystal Structure Analysis of Three Novel Iron(II) Coordination Polymers with Bridging 1,3,5-Tris((1H-1,2,4-triazol-1-yl)methyl)benzene

by Aysenur Limon, Dustin N. Jordan, Till Strothmann, Laure P. Cuignet, Yann Garcia and Christoph Janiak

Crystals 2023, 13(11), 1574; https://doi.org/10.3390/cryst13111574 - 7 Nov 2023

Cited by 1 | Viewed by 2440

Abstract

Three novel iron(II) coordination polymers, namely [Fe(H₂O)₂(ttmb)₂](ClO₄)₂·4H₂O (1), [Fe(H₂O)₂(ttmb)₂](BF₄)₂·4H₂O (2) and [Fe(NCS)₂(ttmb)₂ [...] Read more.

Three novel iron(II) coordination polymers, namely [Fe(H₂O)₂(ttmb)₂](ClO₄)₂·4H₂O (1), [Fe(H₂O)₂(ttmb)₂](BF₄)₂·4H₂O (2) and [Fe(NCS)₂(ttmb)₂] (3), were synthesized with the linker 1,3,5-tris((1H-1,2,4-triazol-1-yl)methyl)benzene (ttmb). The single-crystal structures show that all three compounds form a double-chain structure with the adjacent iron atoms being bridged by two ttmb linkers. The iron(II) ions are octahedrally surrounded by four N4 donor atoms from the 1,2,4-triazol-1-yl groups of four different ttmb linkers which form an equatorial plane and two trans-coordinated aqua ligands in 1 and 2 or isothiocyanato ligands in 3 in the axial positions. In view of the neutral bridging ttmb linker, there is a non-coordinated counter-anion in 1 and 2 (ClO₄ and BF₄, respectively), and a coordinated NCS anion in 3. Compounds 1 and 2 are isostructural. Interestingly, the ttmb linker only utilizes two of its three potentially coordinating triazole groups. All iron(II) coordination networks are colorless or have a light-yellow color, being indicative of the high-spin state. Full article

(This article belongs to the Special Issue Coordination Complexes: Synthesis, Characterization and Application)

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13 pages, 2168 KiB

Open AccessEditor’s ChoiceArticle

Unveiling the Magnetic and Structural Properties of (X₂YZ; X = Co and Ni, Y = Fe and Mn, and Z = Si) Full-Heusler Alloy Microwires with Fixed Geometrical Parameters

by Mohamed Salaheldeen, Valentina Zhukova, Mihail Ipatov and Arcady Zhukov

Crystals 2023, 13(11), 1550; https://doi.org/10.3390/cryst13111550 - 29 Oct 2023

Cited by 9 | Viewed by 1550

Abstract

We studied Ni₂FeSi-, Co₂FeSi-, and Co₂MnSi-based full-Heusler alloy glass-coated microwires with the same geometric parameters, i.e., fixed nucleus and total diameters, prepared using the Taylor–Ulitovsky method. The fabrication of X₂YZ (X = Co and Ni, [...] Read more.

We studied Ni₂FeSi-, Co₂FeSi-, and Co₂MnSi-based full-Heusler alloy glass-coated microwires with the same geometric parameters, i.e., fixed nucleus and total diameters, prepared using the Taylor–Ulitovsky method. The fabrication of X₂YZ (X = Co and Ni, Y = Fe and Mn, and Z = Si)-based glass-coated microwires with fixed geometric parameters is quite challenging due to the different sample preparation conditions. The XRD analysis showed a nanocrystalline microstructure for all the samples. The space groups Fm3¯m (FCC) and Im3¯m (BCC) with disordered B2 and A2 types are observed for Ni₂FeSi and Co₂FeSi, respectively. Meanwhile, a well-defined, ordered L2₁ type was observed for Co₂MnSi GCMWs. The change in the positions of Ni, Co and Mn, Fe in X₂YSi resulted in a variation in the lattice cell parameters and average grain size of the sample. The room-temperature magnetic behavior showed a dramatic change depending on the chemical composition, where Ni₂FeSi MWs showed the highest coercivity (H_c) compared to Co₂FeSi and Co₂MnSi MWs. The H_c value of Ni₂FeSi MWs was 16 times higher than that of Co₂MnSi MWs and 3 times higher than that of Co₂FeSi MWs. Meanwhile, the highest reduced remanence was reported for Co₂FeSi MWs (Mr = 0.92), being about 0.82 and 0.22 for Ni₂FeSi and Co₂MnSi MWs, respectively. From the analysis of the temperature dependence of the magnetic properties (H_c and M_r) of X₂YZ MWs, we deduced that the H_c showed a stable tendency for Co₂MnSi and Co₂FeSi MWs. Meanwhile, two flipped points were observed for Ni₂FeSi MWs, where the behavior of H_c changed with temperature. For M_r, a monotonic increase on decreasing the temperature was observed for Co₂FeSi and Ni₂FeSi MWs, and it remained roughly stable for Co₂MnSi MWs. The thermomagnetic curves at low magnetic field showed irreversible magnetic behavior for Co₂MnSi and Co₂FeSi MWs and regular ferromagnetic behavior for Ni₂FeSi MWs. The current result illustrates the ability to tailor the structure and magnetic behavior of X₂YZ MWs at fixed geometric parameters. Additionally, a different behavior was revealed in X₂YZ MWs depending on the degree of ordering and element distribution. The tunability of the magnetic properties of X₂YZ MWs makes them suitable for sensing applications. Full article

(This article belongs to the Topic Advanced Magnetic Alloys)

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11 pages, 984 KiB

Open AccessEditor’s ChoiceArticle

Raman Spectroscopic Study of Ruddlesden—Popper Tetragonal Sr₂VO₄

by Romain Viennois, David Bourgogne and Julien Haines

Crystals 2023, 13(11), 1541; https://doi.org/10.3390/cryst13111541 - 27 Oct 2023

Cited by 2 | Viewed by 1585

Abstract

The lattice dynamics of tetragonal Sr₂VO₄ with a Ruddlesden—Popper-layered crystal structure was studied via Raman spectroscopy. We observed three of the four expected Raman-active modes under ambient conditions. Mode Grüneisen parameters and the implicit fractions of two A_1g Raman-active [...] Read more.

The lattice dynamics of tetragonal Sr₂VO₄ with a Ruddlesden—Popper-layered crystal structure was studied via Raman spectroscopy. We observed three of the four expected Raman-active modes under ambient conditions. Mode Grüneisen parameters and the implicit fractions of two A_1g Raman-active modes were determined from high-pressure and high-temperature Raman spectroscopy experiments. The low-energy A_1g Raman-active mode involving Sr motions along the c direction has a large isothermal Grüneisen parameter about seven times larger than that of the high-energy A_1g Raman-active mode involving apical O motions along the c direction and is, therefore, more anharmonic. The thermodynamic Grüneisen parameter is significantly smaller in Sr₂VO₄ than in Sr₂TiO₄ due to the smaller Grüneisen parameter of the high-energy A_1g Raman-active mode and other vibrational modes that still need to be identified. The explicit contribution of the low-energy A_1g Raman-active mode is negative, and the implicit contribution due to volume change is much larger. Both volume implicit and anharmonic explicit contributions of the high-energy A_1g Raman-active mode have similar positive values. The Raman experiment in the air shows that Sr₂VO₄ begins to decompose above 200 °C. Full article

(This article belongs to the Special Issue Raman Scattering in Optical Crystals (Volume II))

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12 pages, 3460 KiB

Open AccessEditor’s ChoiceArticle

Fixed-Target Pink-Beam Serial Synchrotron Crystallography at Pohang Light Source II

by Yongsam Kim and Ki Hyun Nam

Crystals 2023, 13(11), 1544; https://doi.org/10.3390/cryst13111544 - 27 Oct 2023

Cited by 4 | Viewed by 1819

Abstract

Serial crystallography (SX) enables the determination of the structure of macromolecules or small molecules with minimal radiation damage. In particular, biomolecule structures determined using the SX technique have the advantage of providing room-temperature crystal structures with high biological relevance. The SX technique requires [...] Read more.

Serial crystallography (SX) enables the determination of the structure of macromolecules or small molecules with minimal radiation damage. In particular, biomolecule structures determined using the SX technique have the advantage of providing room-temperature crystal structures with high biological relevance. The SX technique requires numerous crystals to be collected to complete three-dimensional structural information. To minimize crystal sample consumption, we introduced SX data collection with fixed-target (FT) pink-beam serial synchrotron crystallography (SSX) at the 1C beamline of Pohang Light Source II. A new sample holder consisting of a magnetic frame with a nylon mesh was developed for easy sample handling. The FT-pink-SSX diffraction data were collected by continuously scanning X-rays using a stepping motor. The room-temperature structures of glucose isomerase and lysozyme were successfully determined at a resolution of 1.7 and 2.2 Å, respectively. The use of pink-beam FT-SSX in experimental applications and data acquisition for large beam sizes is discussed. Our results provide useful information for future pink-beam SSX and SX data collection using large X-ray beams. Full article

(This article belongs to the Special Issue X-Ray Protein Crystallography)

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15 pages, 8814 KiB

Open AccessEditor’s ChoiceArticle

Crystal Growth and the Structure of a New Quaternary Adamantine Cu☐GaGeS₄

by Yvonne Tomm, Daniel M. Többens, Galina Gurieva and Susan Schorr

Crystals 2023, 13(11), 1545; https://doi.org/10.3390/cryst13111545 - 27 Oct 2023

Viewed by 1537

Abstract

Single crystals of quaternary adamantine-type Cu☐GaGeS₄ were grown using the chemical vapor transport technique, with iodine as the transport agent. Dark red transparent crystals were grown in a temperature gradient of ΔT = 900–750 °C. Chemical characterization by X-ray fluorescence showed the [...] Read more.

Single crystals of quaternary adamantine-type Cu☐GaGeS₄ were grown using the chemical vapor transport technique, with iodine as the transport agent. Dark red transparent crystals were grown in a temperature gradient of ΔT = 900–750 °C. Chemical characterization by X-ray fluorescence showed the off-stoichiometric composition of Cu☐GaGeS₄ crystals—in particular, a slight Ge deficiency was observed. By X-ray diffraction, Cu☐GaGeS₄ was found to adopt the chalcopyrite-type structure with the space group

I \bar{4} 2 d

. Cation distribution in this structure was analyzed by multiple energy anomalous synchrotron X-ray diffraction, and it was found that Cu and vacancies occupied the 4a site, whereas Ga and Ge occupied the 4b site. The band gap energies of several off-stoichiometric Cu☐GaGeS₄ crystals were determined by UV-Vis spectroscopy and ranged from 2.1 to 2.4 eV. A non-linear correlation of the band gap energy with the Ge content of the compound was shown to follow the usual bowing behavior of semiconductor alloys, with a bowing parameter of

b

= −1.45 (0.08). Full article

(This article belongs to the Section Materials for Energy Applications)

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12 pages, 1856 KiB

Open AccessEditor’s ChoiceReview

Nitride Wide-Bandgap Semiconductors for UV Nonlinear Optics

by Shihang Li and Lei Kang

Crystals 2023, 13(11), 1536; https://doi.org/10.3390/cryst13111536 - 26 Oct 2023

Cited by 1 | Viewed by 1957

Abstract

Nitride wide-bandgap semiconductors possess a wide tunable energy bandgap and abundant coordination anionic groups. This suggests their potential to display nonlinear optical (NLO) properties in the UV wavelength spectrum. This paper reports recent progress and material discoveries in exploring UV NLO structures using [...] Read more.

Nitride wide-bandgap semiconductors possess a wide tunable energy bandgap and abundant coordination anionic groups. This suggests their potential to display nonlinear optical (NLO) properties in the UV wavelength spectrum. This paper reports recent progress and material discoveries in exploring UV NLO structures using nitrides. The study emphasizes their underlying structure–property correlations in order to provide a summary of the potential performance and application value of important nitride NLO crystals. Additionally, the text underscores the benefits of nitrides in terms of optical transparency, second-harmonic-generation effects, and the birefringent phase matching output wavelength limits, while addressing current issues in terms of theoretical outlook and experimental exploration. Full article

(This article belongs to the Special Issue Advances of Nonlinear Optical Materials)

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15 pages, 2426 KiB

Open AccessEditor’s ChoiceArticle

EXtra-Xwiz: A Tool to Streamline Serial Femtosecond Crystallography Workflows at European XFEL

by Oleksii Turkot, Fabio Dall’Antonia, Richard J. Bean, Juncheng E, Hans Fangohr, Danilo E. Ferreira de Lima, Sravya Kantamneni, Henry J. Kirkwood, Faisal H. M. Koua, Adrian P. Mancuso, Diogo V. M. Melo, Adam Round, Michael Schuh, Egor Sobolev, Raphaël de Wijn, James J. Wrigley and Luca Gelisio

Crystals 2023, 13(11), 1533; https://doi.org/10.3390/cryst13111533 - 24 Oct 2023

Cited by 4 | Viewed by 2131

Abstract

X-ray free electron lasers deliver photon pulses that are bright enough to observe diffraction from extremely small crystals at a time scale that outruns their destruction. As crystals are continuously replaced, this technique is termed serial femtosecond crystallography (SFX). Due to its high [...] Read more.

X-ray free electron lasers deliver photon pulses that are bright enough to observe diffraction from extremely small crystals at a time scale that outruns their destruction. As crystals are continuously replaced, this technique is termed serial femtosecond crystallography (SFX). Due to its high pulse repetition rate, the European XFEL enables the collection of rich and extensive data sets, which are suited to study various scientific problems, including ultra-fast processes. The enormous data rate, data complexity, and the nature of the pixelized multimodular area detectors at the European XFEL pose severe challenges to users. To streamline the analysis of the SFX data, we developed the semiautomated pipeline EXtra-Xwiz around the established CrystFEL program suite, thereby processing diffraction patterns on detector frames into structure factors. Here we present EXtra-Xwiz, and we introduce its architecture and use by means of a tutorial. Future plans for its development and expansion are also discussed. Full article

(This article belongs to the Special Issue Diffractive Imaging of Crystalline Materials at XFELs and Synchrotrons)

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9 pages, 3772 KiB

Open AccessEditor’s ChoiceArticle

Spin-Polarized 2D Electron Gas at the EuTiO₃/EuO Interface

by Jonathan Gjerde, Mahmoud Hammouri and Radi A. Jishi

Crystals 2023, 13(10), 1511; https://doi.org/10.3390/cryst13101511 - 18 Oct 2023

Viewed by 1640

Abstract

Perovskite oxide heterostructures have provided opportunities for new technologies and materials with novel properties.In particular, researchers have been interested in the magnetism and two-dimensional electron gases that form at the interface of many of these heterostructures. Often, these properties are due to polar [...] Read more.

Perovskite oxide heterostructures have provided opportunities for new technologies and materials with novel properties.In particular, researchers have been interested in the magnetism and two-dimensional electron gases that form at the interface of many of these heterostructures. Often, these properties are due to polar discontinuities, but here we use first-principles calculations to examine a heterostructure whose elements, EuO and EuTiO

_{3}

, are both non-polar, yet are still conductive due to oxygen vacancies. Furthermore, the free electrons at the interface of this heterostructure are predicted to be spin-polarized, opening up possibilities for future research and devices. Full article

(This article belongs to the Section Materials for Energy Applications)

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11 pages, 3330 KiB

Open AccessEditor’s ChoiceArticle

Ultrahigh-Density Superhard Hexagonal BN and SiC with Quartz Topology from Crystal Chemistry and First Principles

by Samir F. Matar and Vladimir L. Solozhenko

Crystals 2023, 13(10), 1498; https://doi.org/10.3390/cryst13101498 - 14 Oct 2023

Cited by 3 | Viewed by 1573

Abstract

Based on superdense C₆ with a quartz (qtz) topology, new ultrahigh-density hexagonal binary phases, qtz BN and qtz SiC, were identified via full geometry structure relaxations and ground state energies using calculations based on the quantum density functional theory (DFT) [...] Read more.

Based on superdense C₆ with a quartz (qtz) topology, new ultrahigh-density hexagonal binary phases, qtz BN and qtz SiC, were identified via full geometry structure relaxations and ground state energies using calculations based on the quantum density functional theory (DFT) with a gradient GGA exchange–correlation XC functional. Like qtz C₆, with respect to diamond, the resulting binary qtz BN and qtz SiC were found to be less cohesive than cubic BN and cubic SiC, respectively, but were confirmed to be mechanically (elastic constants) and dynamically (phonon band structures) stable. Higher densities of the new phases correlate with higher hardness values compared to cubic BN and cubic SiC. In contrast to the regular tetrahedra that characterize the cubic BN and SiC phases, the corner-sharing tetrahedra in the new phases are distorted, which accounts for their exceptional density and hardness. All three qtz phases were found to be semiconducting to insulators, with reduced band gaps compared to diamond, cubic BN, and cubic SiC. Full article

(This article belongs to the Special Issue First Principles Calculation for Crystalline Materials)

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11 pages, 6967 KiB

Open AccessEditor’s ChoiceArticle

Side-Chain Labeling Strategy for Forming Self-Sorted Columnar Liquid Crystals from Binary Discotic Systems

by Tsuneaki Sakurai, Kenichi Kato and Masaki Shimizu

Crystals 2023, 13(10), 1473; https://doi.org/10.3390/cryst13101473 - 10 Oct 2023

Cited by 2 | Viewed by 2263

Abstract

The spontaneous formation of self-sorted columnar structures of electron-donating and accepting π-conjugated molecules is attractive for photoconducting and photovoltaic properties. However, the simple mixing of donor–acceptor discotic molecules usually results in the formation of mixed-stacked or alternating-stacked columns. As a new strategy for [...] Read more.

The spontaneous formation of self-sorted columnar structures of electron-donating and accepting π-conjugated molecules is attractive for photoconducting and photovoltaic properties. However, the simple mixing of donor–acceptor discotic molecules usually results in the formation of mixed-stacked or alternating-stacked columns. As a new strategy for overcoming this problem, here, we report the “side-chain labeling” approach using binary discotic systems and realize the preferential formation of such self-sorted columnar structures in a thermodynamically stable phase. The demonstrated key strategy involves the use of hydrophobic and hydrophilic side chains. The prepared blend is composed of liquid crystalline phthalocyanine with branched alkyl chains (H₂Pc) and perylenediimide (PDI) carrying alkyl chains at one side and triethyleneglycol (TEG) chains at the other side (PDI_C12/TEG). To avoid the thermodynamically unfavorable contact among hydrophobic and hydrophilic chains, PDI_C12/TEG self-assembles to stack up on top of each other and H₂Pc as well, forming a homo-stacked pair of columns (self-sort). Importantly, H₂Pc and PDI_C12/TEG in the blend are macroscopically miscible and uniform, and mesoscopically segregated. The columnar liquid crystalline microdomains of H₂Pc and PDI_C12/TEG are homeotropically aligned in a glass sandwiched cell. The “labeling” strategy demonstrated here is potentially applicable to any binary discotic system and enables the preferential formation of self-sorted columnar structures. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in Japan)

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14 pages, 3462 KiB

Open AccessEditor’s ChoiceArticle

Off-Eutectic Growth Model for Solidifying Alloy from an Undercooled State

by Junfeng Xu and Peter K. Galenko

Crystals 2023, 13(10), 1453; https://doi.org/10.3390/cryst13101453 - 29 Sep 2023

Viewed by 1581

Abstract

Classical eutectic growth models are based on the use of eutectic composition. These models neglect the effect of primary phase formation, and their direct use in the rapid solidification process of off-eutectic (hypoeutectic and hypereutectic) alloys is absent. Combining the effect of the [...] Read more.

Classical eutectic growth models are based on the use of eutectic composition. These models neglect the effect of primary phase formation, and their direct use in the rapid solidification process of off-eutectic (hypoeutectic and hypereutectic) alloys is absent. Combining the effect of the primary phase in the eutectic transformation and an off-eutectic composition, the solidification growth model is derived in the present work. The effect of the model and material parameters on solidification kinetics is discussed in comparison with experimental data. Computational results on the off-eutectic growth model show that the model agrees well with experimental data on the solidification kinetics of Ni–B and Ti–Si alloys. Full article

(This article belongs to the Special Issue Phase Transition in External Fields (2nd Edition))

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11 pages, 4133 KiB

Open AccessEditor’s ChoiceArticle

Flux Growth and Characterization of Bulk InVO₄ Crystals

by Olesia Voloshyna, Mikhail V. Gorbunov, Daria Mikhailova, Andrey Maljuk, Silvia Seiro and Bernd Büchner

Crystals 2023, 13(10), 1439; https://doi.org/10.3390/cryst13101439 - 28 Sep 2023

Cited by 1 | Viewed by 1631

Abstract

The flux growth of InVO₄ bulk single crystals has been explored for the first time. The reported eutectic composition at a ratio of V₂O₅:InVO₄ = 1:1 could not be used as a self-flux since no sign of [...] Read more.

The flux growth of InVO₄ bulk single crystals has been explored for the first time. The reported eutectic composition at a ratio of V₂O₅:InVO₄ = 1:1 could not be used as a self-flux since no sign of melting was observed up to 1100 °C. Crystals of InVO₄ of typical size 0.5 × 1 × 7 mm³ were obtained using copper pyrovanadate (Cu₂V₂O₇) as a flux, using Pt crucibles. X-ray powder diffraction confirmed the orthorhombic Cmcm structure. Rests of the flux material were observed on the sample surface, with occasional traces of Pt indicating some level of reaction with the crucible. X-ray absorption spectroscopy showed that oxidation states of indium and vanadium ions are +3 and +5, respectively. The size and high quality of the obtained InVO₄ crystals makes them excellent candidates for further study of their physical properties. Full article

(This article belongs to the Special Issue Application of X-ray and Electron to Crystal Structure Characterization)

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18 pages, 4236 KiB

Open AccessEditor’s ChoiceArticle

A Coupled Approach to Compute the Dislocation Density Development during Czochralski Growth and Its Application to the Growth of High-Purity Germanium (HPGe)

by Wolfram Miller, Andrejs Sabanskis, Alexander Gybin, Kevin-P. Gradwohl, Arved Wintzer, Kaspars Dadzis, Jānis Virbulis and Radhakrishnan Sumathi

Crystals 2023, 13(10), 1440; https://doi.org/10.3390/cryst13101440 - 28 Sep 2023

Cited by 3 | Viewed by 1746

Abstract

The evolution of the dislocation density during Czochralski growth is computed by the combination of global thermal calculations and local computation of the stress and dislocation density in the crystal. The global simulation was performed using the open-source software Elmer (version 8.4) and [...] Read more.

The evolution of the dislocation density during Czochralski growth is computed by the combination of global thermal calculations and local computation of the stress and dislocation density in the crystal. The global simulation was performed using the open-source software Elmer (version 8.4) and the local simulation with the open-source software MACPLAS (version of 23.1.2023). Interpolation both in space and time was used to transfer the boundary conditions from the global simulations to the local model, which uses a different mesh discretization and a considerably smaller time step. We applied this approach to the Czochralski growth of a high-purity Ge crystal. The heater power change predicted by the global model as well as the final dislocation density distribution in the crystal simulated by the local model are correlated to the experimental results. Full article

(This article belongs to the Special Issue Advances in Crystal Growth: Pioneering Materials for Tomorrow's Technologies)

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