Crystals

16 pages, 1930 KB

Open AccessArticle

Comprehensive Spectroscopic Study of Competing Recombination Channels and Thermal Quenching Mechanisms in β-Ga₂O₃ Single Crystals

by Aizat Bakytkyzy, Zhakyp T. Karipbayev, Alma Dauletbekova, Amangeldy M. Zhunusbekov, Meldra Kemere, Marina Konuhova, Anatolijs Sarakovskis and Anatoli I. Popov

Crystals 2025, 15(10), 909; https://doi.org/10.3390/cryst15100909 - 21 Oct 2025

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Abstract

This work investigates a comprehensive temperature-dependent photoluminescence (PL) study (7–300 K) of β-Ga₂O₃ single crystals under 250 nm excitation. The emission consists of three competing bands at ~3.55 eV (J₁), ~3.37 eV (J₂), and ~3.07 eV [...] Read more.

This work investigates a comprehensive temperature-dependent photoluminescence (PL) study (7–300 K) of β-Ga₂O₃ single crystals under 250 nm excitation. The emission consists of three competing bands at ~3.55 eV (J₁), ~3.37 eV (J₂), and ~3.07 eV (J₃), exhibiting a redshift, band broadening, and a crossover near ~140 K with increasing temperature. The novelty of this study lies in the first quantitative investigation of the temperature-dependent photoluminescence of undoped β-Ga₂O₃ single crystals, revealing activation, trap-release, and phonon-coupling parameters that define the competition between STE (Self-trapped exciton)- and DAP-related emission channels. A two-channel Arrhenius analysis of global thermal quenching at E_max (at maximum PL), J₁, and J₂ reveals a common shallow barrier (E₁ = 7–12 meV) alongside deeper, band-specific barriers (E₂ = 27 meV for J₁ and 125 meV for J₂). The J₃ band shows non-monotonic intensity (dip–peak–quench) reproduced by a trap-assisted generation model with a release energy E_rel = 50 meV. Linewidth analysis yields effective phonon energies (E_ph ≈ 40–46 meV), indicating strong electron–phonon coupling and a transition to multi-phonon broadening at higher temperatures. These results establish a coherent picture of thermally driven redistribution from near-edge STE-like states to deeper defect centers and provide quantitative targets (activation and phonon energies) for defect engineering in β-Ga₂O₃-based optoelectronic and scintillation materials. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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10 pages, 3403 KB

Open AccessArticle

Microstructural and XRD Investigations on Zn After Plastic Deformation

by Alessandra Ceci, Girolamo Costanza and Maria Elisa Tata

Crystals 2025, 15(10), 908; https://doi.org/10.3390/cryst15100908 - 21 Oct 2025

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Abstract

This work presents a microstructural analysis and X-ray diffraction (XRD) investigation of the plastic deformation in commercially pure, single-phase hexagonal close-packed (hcp) Zn subjected to rolling and tensile tests up to failure. Samples were examined by optical microscope and XRD; hardness was assessed [...] Read more.

This work presents a microstructural analysis and X-ray diffraction (XRD) investigation of the plastic deformation in commercially pure, single-phase hexagonal close-packed (hcp) Zn subjected to rolling and tensile tests up to failure. Samples were examined by optical microscope and XRD; hardness was assessed by Vickers microhardness. High-resolution diffraction profiles with Kα1/Kα2 deconvolution were used to identify deformation-induced texture and to estimate the dislocation density. Results show that rolling (40% thickness reduction) and tensile test change texture and cause peak shifts and broadening, with corresponding microstructural changes. Microhardness changes from 28–45 HV (annealed) to 30–50 HV after deformation. After rolling, the texture (002) is the most intense reflection and (004) increases without significant angular shifts. Tensile tests induce low-angle shifts of (101) and (004), as well as selective texture changes (appearance of (103) and (110)). The (101) full width at half maximum increases from β(2θ) = 0.115° (annealed) to 0.160° (rolled) and 0.140° (after tensile test), yielding dislocation densities from 2.73 × 10⁶ cm⁻² (annealed) to 3.03 × 10¹¹ cm⁻² (rolled) and 3.38 × 10¹⁰ cm⁻² (after tensile test). Finally, this study quantifies the XRD parameters (full width at half maximum, angular shifts and dislocation density). Plastic deformation of pure Zn leads to significant microstructural changes, including grain refinement, the generation of dislocations, and the formation of new crystallographic orientations, which are then observable in XRD patterns as peak broadening, shifts, and texture development. The severity of these effects depends on the level of deformation. Full article

(This article belongs to the Special Issue Microstructure and Characterization of Crystalline Materials)

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13 pages, 3441 KB

Open AccessArticle

Line-Defect Phononic Crystal Structure for Directional Enhancement Detection of Weak Acoustic Signals

by Shijie Zhang, Jinling Mu, Jiawei Xiao and Huiqiang Xu

Crystals 2025, 15(10), 907; https://doi.org/10.3390/cryst15100907 - 18 Oct 2025

Viewed by 450

Abstract

Effective detection of acoustic signals plays a crucial role in numerous fields, including industrial equipment fault prediction and environmental monitoring. Acoustic sensing technology, owing to its substantial information carrying capacity and non-contact measurement advantages, has garnered widespread attention in relevant applications. However, the [...] Read more.

Effective detection of acoustic signals plays a crucial role in numerous fields, including industrial equipment fault prediction and environmental monitoring. Acoustic sensing technology, owing to its substantial information carrying capacity and non-contact measurement advantages, has garnered widespread attention in relevant applications. However, the effective detection of weak target acoustic signals amidst strong noise interference remains a critical challenge in this field. The core bottleneck lies in the difficulty of traditional detection methods to simultaneously achieve both high sensitivity and high directionality. To address this limitation, this work proposes a line-defect phononic crystal (PnC) structure that enables directional enhancement and detection of weak target signals under intense spatial noise interference by coupling defect state localization characteristics with anisotropy mechanisms. Through theoretical derivation and finite element numerical simulation, the directional enhancement properties of this structure were systematically validated. Furthermore, numerical simulations were conducted to validate the detection of weak harmonic signals and weak bearing fault signals under strong spatial noise interference. The results demonstrate that this line-defect phononic crystal (PnC) structure exhibits high feasibility and outstanding performance in detecting weak acoustic signals. This work provides novel insights for developing new acoustic detection methods combining high sensitivity with high directivity, showcasing unique advantages and broad application prospects in acoustic signal sensing, enhancement, and localization. Full article

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

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15 pages, 3244 KB

Open AccessArticle

Synthesis, Structure, and Investigation of Terbium(III) Luminescent Metal-Organic Framework Based on (N-Morpholyl)-Functionalized 1,10-Phenanthroline

by Anna A. Ovchinnikova, Pavel A. Demakov, Alexey A. Ryadun, Alexander M. Agafontsev, Vladimir P. Fedin and Danil N. Dybtsev

Crystals 2025, 15(10), 906; https://doi.org/10.3390/cryst15100906 - 18 Oct 2025

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Abstract

4,7-di(N-morpholyl)-1,10-phenanthroline (morphen) was introduced for the first time as a ligand for the construction of metal–organic frameworks. The obtained MOF compound has the crystallographic formula {[Tb₂(morphen)₂Br₂(chdc)₂]}_n (1; chdc²⁻ = trans-1,4-cyclohexanedicarboxylate) [...] Read more.

4,7-di(N-morpholyl)-1,10-phenanthroline (morphen) was introduced for the first time as a ligand for the construction of metal–organic frameworks. The obtained MOF compound has the crystallographic formula {[Tb₂(morphen)₂Br₂(chdc)₂]}_n (1; chdc²⁻ = trans-1,4-cyclohexanedicarboxylate) and is based on binuclear {Tb₂(N^N)₂Br₂(OOCR)₄} carboxylate blocks, interlinked by ditopicchdc linkers into a layered coordination network with sql topology. Purity and integrity of the as-synthesized 1 were confirmed by common characterization techniques, such as PXRD, CHN, IR, and TGA. Compound 1 was found to be hydrolytically stable and possessing typical green emission for Tb(III) complexes. Exploiting its high stability, luminescent 1@PVA films were successfully prepared from 1 and polyvinyl alcohol (PVA) through the water solution drying approach. Full article

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

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12 pages, 4432 KB

Open AccessArticle

Preliminary Serial Femtosecond Crystallography Studies of Myoglobin from Equine Skeletal Muscle

by Jaehyun Park, Sehan Park and Ki Hyun Nam

Crystals 2025, 15(10), 905; https://doi.org/10.3390/cryst15100905 - 18 Oct 2025

Viewed by 508

Abstract

Myoglobin (Mb), a heme-containing protein, plays crucial roles in storing and transporting oxygen in muscle cells. Various Mb structures have been extensively determined using conventional cryogenic crystallography, providing valuable information for understanding the molecular mechanisms of the protein. However, this approach has limitations [...] Read more.

Myoglobin (Mb), a heme-containing protein, plays crucial roles in storing and transporting oxygen in muscle cells. Various Mb structures have been extensively determined using conventional cryogenic crystallography, providing valuable information for understanding the molecular mechanisms of the protein. However, this approach has limitations attributable to cryogenic temperatures and radiation damage. Serial femtosecond crystallography (SFX) using X-ray free-electron lasers is an emerging technique that enables the determination of biologically relevant room-temperature structures without causing radiation damage. In this study, we assessed the crystallization, collection, and processing of SFX diffraction data of Mb from equine skeletal muscle. Needle- and needle cluster-shaped Mb crystals were obtained using the microbatch method. Fixed-target SFX data collection was performed at the Pohang Accelerator Laboratory X-ray Free Electron Laser, yielding 1389 indexed diffraction patterns. The phase problem was solved by molecular replacement. The preliminary Mb structure determined at 2.3-Å resolution in this study exhibited subtle structural differences in the heme environment compared with previously reported Mb structures determined by SFX. These results both confirm the feasibility of myoglobin SFX experiments and establish a foundation for future time-resolved studies aiming to visualize ligand binding and oxygen transport. Full article

(This article belongs to the Section Biomolecular Crystals)

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14 pages, 4778 KB

Open AccessArticle

Synthesis of Multidoped Zirconia by Hydrothermal Method with Sequential Annealing

by Yuriy Alexsandrovich Garanin, Rafael Iosifivich Shakirzyanov, Dmitriy Igorevich Shlimas, Milana Abasovna Saidullayeva, Daryn Boranbaevich Borgekov and Malik Erlanovich Kaliyekperov

Crystals 2025, 15(10), 904; https://doi.org/10.3390/cryst15100904 - 17 Oct 2025

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Abstract

Over more than half a century of using zirconia in technology and industry, researchers have faced several challenges related to the performance of this material. It is believed that some issues regarding the low performance of the zirconia ceramics can be solved by [...] Read more.

Over more than half a century of using zirconia in technology and industry, researchers have faced several challenges related to the performance of this material. It is believed that some issues regarding the low performance of the zirconia ceramics can be solved by using a multidoping strategy. In this study, nanoparticles with the composition (1 − x)⸱ZrO₂ − x⸱MD (where MD—multi-dopant Y:Ce:Mg:Ca with cation relationship 1:1:1:1 and x = 0.05–0.25 mol. %) were synthesized using a hydrothermal method followed by annealing. XRD and Raman spectroscopy analyses demonstrated that in the concentration range of x = 0.10–0.25 mol.%, the only detectable phase in the synthesized samples was the tetragonal phase of zirconia. SEM analysis revealed that the size of the final particles ranged from 20 to 50 nm. It was demonstrated that using obtained nanoparticles as precursors for sintering leads to the formation of multiphase ceramics. The microhardness and biaxial flexural strength of the ceramic samples vary depending on the dopant concentration in the range of 600–1400 HV and 25–200 MPa respectively. Mechanical properties mostly depend on porosity and grain size in the sintered material. The study shows that the multidoping strategy has high potential to obtain new constructional ceramics and components for solid oxide fuel cells. Full article

(This article belongs to the Special Issue Ceramic Materials: Structural, Mechanical and Dielectric Properties)

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17 pages, 5457 KB

Open AccessArticle

Synthesis, Reaction Process, and Mechanical Properties of Medium-Entropy (TiVNb)₂AlC MAX Phase

by Lexing Che, Mingdong Bao, Zhihua Sun and Yingwen Cao

Crystals 2025, 15(10), 903; https://doi.org/10.3390/cryst15100903 - 17 Oct 2025

Viewed by 385

Abstract

The synthesis, reaction process, and mechanical properties of medium-entropy (TiVNb)₂AlC MAX phase materials were investigated. The Ti, V, Nb, Al, and C powders were mixed and sintered by the powder metallurgy method. The experimental results showed that the highest purity M [...] Read more.

The synthesis, reaction process, and mechanical properties of medium-entropy (TiVNb)₂AlC MAX phase materials were investigated. The Ti, V, Nb, Al, and C powders were mixed and sintered by the powder metallurgy method. The experimental results showed that the highest purity M₂AlC phase with a mass fraction of 95.8% was obtained when the raw material ratio was M(Ti:V:Nb):Al:C = 2:1.2:0.7 and the sintering temperature was 1450 °C. In order to explore the sintering process reactions and optimize the purity of sintered products, sintering was carried out under different temperatures and various molar ratios of raw materials. During the sintering process, the metal elements firstly reacted with aluminum to generate intermetallic compounds (IMCs), and with the increase in temperature, the IMCs gradually reacted with carbon to generate M₂AlC. Mechanical property tests revealed that the Vickers hardness of the medium-entropy (TiVNb)₂AlC material was 6.52 GPa, significantly higher than both the theoretical prediction based on the rule of mixtures and the hardness of traditional MAX phases. The severe lattice distortions in the polymeric solid solution structure contributed to this significant increase in hardness. In addition, the medium-entropy (TiVNb)₂AlC exhibited temperature-dependent friction behavior within the temperature range of room temperature to 400 °C, with the lowest friction coefficient observed at 200 °C when the sample was in contact with the bearing steel. This study provided an important theoretical and experimental basis for the synthesis and future application of medium-entropy MAX phase materials. Full article

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

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18 pages, 5563 KB

Open AccessArticle

Research on Ultrasonic-Assistance Microarc Plasma Polishing Method for 4H-SiC

by Feilong Liu, Jiayi Yue, Jianhua Shi, Shujuan Li, Yanfei Zhang and Zhenchao Yang

Crystals 2025, 15(10), 902; https://doi.org/10.3390/cryst15100902 - 17 Oct 2025

Viewed by 330

Abstract

Silicon carbide (SiC) is widely used in high-power, high-frequency, and high-temperature electronic devices due to its excellent physical and chemical properties. However, its high hardness and chemical inertness make it difficult to achieve efficient and damage-free ultra-smooth surface processing with traditional polishing methods. [...] Read more.

Silicon carbide (SiC) is widely used in high-power, high-frequency, and high-temperature electronic devices due to its excellent physical and chemical properties. However, its high hardness and chemical inertness make it difficult to achieve efficient and damage-free ultra-smooth surface processing with traditional polishing methods. This paper proposes a novel ultrasonic-assistance microarc plasma polishing (UMPP) method for high-quality and high-efficiency polishing of 4H-SiC. This study introduces a novel Ultrasonic-assisted Microarc Plasma Polishing (UMPP) method for achieving high-efficiency, high-quality surface finishing of 4H-SiC. The technique innovatively combines ultrasonic vibration with microarc plasma oxidation in a neutral NaCl electrolyte to overcome the limitations of conventional polishing methods. The UMPP process first generates a soft, porous oxide layer (primarily SiO₂) on the SiC surface through plasma discharge, which is then gently removed using soft CeO₂ abrasives. The key finding is that ultrasonic assistance synergistically enhances the oxidation process, leading to a thicker and more porous oxide layer that is more easily removed. Experimental results demonstrate that UMPP achieves a remarkably high material removal rate (MRR) of 21.7 μm/h while simultaneously delivering an ultra-smooth surface with a roughness (Ra) of 0.54 nm. Compared to the process without ultrasonic assistance, UMPP provides a 21.9% increase in MRR and a 28% reduction in Ra. This work establishes UMPP as a highly promising and efficient polishing strategy for hard and inert materials like SiC, offering a superior combination of speed and surface quality that is difficult to achieve with existing techniques. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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15 pages, 1977 KB

Open AccessArticle

Single-Crystal X-Ray Diffraction Studies of Derivatives of Phenolphthalein (3,3-Bis(4-hydroxyphenyl)isobenzofuran-1(3H)-one)

by Brian A. Chalmers, David B. Cordes, Aidan P. McKay, Iain L. J. Patterson, Russell J. Pearson, Joscelyn H. Sequeira-Shuker, Iain A. Smellie and Nadiia Vladymyrova

Crystals 2025, 15(10), 901; https://doi.org/10.3390/cryst15100901 - 17 Oct 2025

Viewed by 537

Abstract

An investigation of the molecular structure of a series of phenolphthalein derivatives is presented. The X-ray structures of thymolphthalein, 2,5-dimethylphenolphthalein, and 2,6-dimethylphenolphthalein have been determined for the first time. Furthermore, a series of related 3-(4-hydroxy-dialkyl)-3-(4-hydroxyphenyl)isobenzofuran-1(3H)-ones have also been prepared, and X-ray [...] Read more.

An investigation of the molecular structure of a series of phenolphthalein derivatives is presented. The X-ray structures of thymolphthalein, 2,5-dimethylphenolphthalein, and 2,6-dimethylphenolphthalein have been determined for the first time. Furthermore, a series of related 3-(4-hydroxy-dialkyl)-3-(4-hydroxyphenyl)isobenzofuran-1(3H)-ones have also been prepared, and X-ray structures obtained. The present study allows for comparison of the structures of substituted phenolphthalein derivatives, with a particular focus on the effect of different alkyl groups on the structures. Full article

(This article belongs to the Section Organic Crystalline Materials)

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14 pages, 4562 KB

Open AccessArticle

Step-Graded III–V Metamorphic Buffers on Ge for High-Efficiency Photovoltaics: Investigation of Strain Relaxation and Morphology Evolution

by Elisabetta Achilli, Nicola Armani, Jacopo Pedrini, Erminio Greco, Salvatore Digrandi, Andrea Fratta, Fabio Pezzoli, Roberta Campesato and Gianluca Timò

Crystals 2025, 15(10), 900; https://doi.org/10.3390/cryst15100900 - 17 Oct 2025

Viewed by 343

Abstract

This work is motivated by the need to enhance efficiency and radiation resistance and reduce weight in high-performance photovoltaic devices, with applications spanning both terrestrial and space environments. Metamorphic buffers are key enablers for reducing defect formation in lattice-mismatched structures, which are among [...] Read more.

This work is motivated by the need to enhance efficiency and radiation resistance and reduce weight in high-performance photovoltaic devices, with applications spanning both terrestrial and space environments. Metamorphic buffers are key enablers for reducing defect formation in lattice-mismatched structures, which are among the most widespread technologies for high-efficiency photovoltaic energy conversion. Although many systems have been created, absolute certainty about the effective relaxation mechanism remains unattained. In this work, MOVPE-grown step-graded buffers with variable In content were obtained on Ge substrates and investigated to identify the critical thresholds that govern strain relaxation and defect formation. The results show that the buffers are fully strained when the In top-layer content is <6.0%, while a degree of relaxation in the entire structure appears when the In top-layer content is >6.0%. In addition, the relaxation phenomenon is paralleled by the formation of a tilt angle between the layers and the substrate. We also found evidence that the appearance of relaxation is not limited to the upper layer but is presented by the structure as a whole. The effects of Te doping inside the InGaAs layers were also investigated: Te does not influence the structure of the crystal, but it introduces a Burstein–Moss blue shift in the photoluminescence energy of about 20 meV. Eventually, to reduce defect formation with the goal of achieving high-efficiency photovoltaic devices, a thick layer with a lower In content was grown onto the overshoot material (In_0.12Ga_0.88As). The results obtained confirm the high quality of the buffers and unveil the critical points, which are responsible for the most important changes in the buffer architecture and should be considered in future material engineering. The results provide valuable insights for the design of high-performance, sustainable photovoltaic devices and contribute to the advancement of III–V semiconductor integration on Ge substrates. Full article

(This article belongs to the Special Issue Crystal Growth of III–V Semiconductors)

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9 pages, 294 KB

Open AccessArticle

Germanium-Based Temperonic Crystal

by Jesus Manzanares-Martinez, Diego Soto-Puebla and Gerardo Morales-Morales

Crystals 2025, 15(10), 899; https://doi.org/10.3390/cryst15100899 - 16 Oct 2025

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Abstract

We propose a germanium-based temperonic crystal consisting of a two-layer unit cell designed to enable interference of thermal waves in the non-Fourier regime. Each layer features temperature-dependent properties, including thermal diffusivity

D (T)

, thermal conductivity

κ (T)

, [...] Read more.

We propose a germanium-based temperonic crystal consisting of a two-layer unit cell designed to enable interference of thermal waves in the non-Fourier regime. Each layer features temperature-dependent properties, including thermal diffusivity

D (T)

, thermal conductivity

κ (T)

, and relaxation time

τ (T)

. Utilizing the Cattaneo-Vernotte model, we predict band gaps in the temperature oscillation frequencies. Our analysis reveals that band gaps emerge when one layer is maintained at 110 K and the other at 50 K; however, these gaps close rapidly as the temperature contrast diminishes or the overall temperature increases. Drawing from the temperonic-crystal paradigm and inspired by recent experimental observations of thermal waves in germanium, this design offers a promising pathway for on-chip control of ultrafast thermal pulses and thermal-management devices in semiconductors. Full article

(This article belongs to the Topic Nanomaterials for Photonics and Optoelectronics: Practical Applications and Advances)

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20 pages, 2245 KB

Open AccessArticle

Incomplete Absorption Correction Results in an Increased Positive Mean Value of Weighted Residuals

by Julian Henn

Crystals 2025, 15(10), 898; https://doi.org/10.3390/cryst15100898 - 16 Oct 2025

Cited by 1 | Viewed by 333

Abstract

Incomplete absorption correction procedures in single-crystal diffraction experiments leave a characteristic trace—a “fingerprint”—in the residuals. Specifically, weak intensities are systematically overestimated, contributing disproportionately and sometimes even dominantly to the chi-square sum in least squares refinements. An analysis of six published crystal structures spanning [...] Read more.

Incomplete absorption correction procedures in single-crystal diffraction experiments leave a characteristic trace—a “fingerprint”—in the residuals. Specifically, weak intensities are systematically overestimated, contributing disproportionately and sometimes even dominantly to the chi-square sum in least squares refinements. An analysis of six published crystal structures spanning a wide range of absorption coefficients reveals a consistent positive shift of the weighted residuals, which were significant for crystals with

> 5.02

mm⁻¹. This shift is all the stronger the greater the absorption coefficient and is accompanied by a proportionally increasing fraction of positive excess residuals. The simultaneous increase in the mean value of the residuals and the fraction of positive excess residuals proves that the shift is not caused by strong reflections or isolated outliers, but rather by the systematic overestimation of many weak intensities. Diagnostic plots and statistical metrics are presented for additional published data sets, supporting the generality of the findings. These findings can support the development of improved methods for absorption correction, which lead to physically meaningful thermal motion parameters even with strong absorption. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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30 pages, 6082 KB

Open AccessReview

Metal–Organic Framework for Plastic Depolymerization and Upcycling

by Kisung Lee, Sumin Han, Minse Kim, Byoung-su Kim, Jeong-Ann Park, Kwang Suk Lim, Suk-Jin Ha and Hyun-Ouk Kim

Crystals 2025, 15(10), 897; https://doi.org/10.3390/cryst15100897 - 16 Oct 2025

Viewed by 929

Abstract

Plastics are essential in modern life but accumulate as waste. Mechanical reprocessing reduces material quality, whereas thermochemical routes require harsh conditions and are costly to upgrade. Together, these factors hinder the large-scale recovery of plastics into equivalent materials. Metal–organic frameworks provide a programmable [...] Read more.

Plastics are essential in modern life but accumulate as waste. Mechanical reprocessing reduces material quality, whereas thermochemical routes require harsh conditions and are costly to upgrade. Together, these factors hinder the large-scale recovery of plastics into equivalent materials. Metal–organic frameworks provide a programmable platform where reticular design fixes porosity and positions well-defined Lewis, Brønsted, redox, and photoredox sites that can preconcentrate oligomers and align scissile bonds for activation. These attributes enable complementary pathways spanning hydrolysis, alcoholysis, aminolysis, photo-oxidation, electrocatalysis, and MOF-derived transformations, with adsorption-guided capture-to-catalysis workflows emerging as integrative schemes. In this review, we establish common figures of merit such as space–time yield, monomer selectivity and purity, energy intensity, site-normalized turnover, and solvent or corrosion footprints. These metrics are connected to design rules that involve active-site chemistry and transport through semi-crystalline substrates. We also emphasize durability under hot aqueous, alcoholic, or oxidative conditions as essential for producing polymer-grade products. Full article

(This article belongs to the Section Macromolecular Crystals)

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12 pages, 8210 KB

Open AccessArticle

Structural and Magnetic Properties of Sputtered Chromium-Doped Sb₂Te₃ Thin Films

by Joshua Bibby, Angadjit Singh, Emily Heppell, Jack Bollard, Barat Achinuq, Julio Alves do Nascimento, Connor Murrill, Vlado K. Lazarov, Gerrit van der Laan and Thorsten Hesjedal

Crystals 2025, 15(10), 896; https://doi.org/10.3390/cryst15100896 - 16 Oct 2025

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Abstract

Magnetron sputtering offers a scalable route to magnetic topological insulators (MTIs) based on Cr-doped Sb₂Te₃. We combine a range of X-ray diffraction (XRD), reciprocal-space mapping (RSM), scanning transmission electron microscopy (STEM), scanning TEM-energy-dispersive X-ray spectroscopy (STEM-EDS), and X-ray absorption [...] Read more.

Magnetron sputtering offers a scalable route to magnetic topological insulators (MTIs) based on Cr-doped Sb₂Te₃. We combine a range of X-ray diffraction (XRD), reciprocal-space mapping (RSM), scanning transmission electron microscopy (STEM), scanning TEM-energy-dispersive X-ray spectroscopy (STEM-EDS), and X-ray absorption spectroscopy, and X-ray magnetic circular dichroism (XAS/XMCD) techniques to study the structure and magnetism of Cr-doped Sb₂Te₃ films. Symmetric

θ

-2

θ

XRD and RSM establish a solubility window. Layered tetradymite order persists up to ∼10 at.-% Cr, while higher doping yields CrTe/Cr₂Te₃ secondary phases. STEM reveals nanocrystalline layered stacking at low Cr and loss of long-range layering at higher Cr concentrations, consistent with XRD/RSM. Magnetometry on a 6% film shows soft ferromagnetism at 5 K. XAS and XMCD at the Cr

L_{2, 3}

edges exhibits a depth dependence: total electron yield (TE; surface sensitive) shows both nominal Cr²⁺ and Cr³⁺, whereas fluorescence yield (FY; bulk sensitive) shows a much higher Cr²⁺ weight. Sum rules applied to TEY give

m_{L} = (0.20 \pm 0.04)

μ_{B}

/Cr, and

m_{S} = (1.6 \pm 0.2)

μ_{B}

/Cr, whereby we note that the applied maximum field (3 T) likely underestimates

m_{S}

. These results define a practical growth window and outline key parameters for MTI films. Full article

(This article belongs to the Special Issue Advances in Thin-Film Materials and Their Applications)

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28 pages, 6980 KB

Open AccessArticle

Improving Weld Stability in Gas Metal Arc Welding: A Data-Driven and Machine Learning Approach

by Elina Mylen Montero Puñales, Guillermo Alvarez Bestard and Sadek Crisóstomo Absi Alfaro

Crystals 2025, 15(10), 895; https://doi.org/10.3390/cryst15100895 - 16 Oct 2025

Viewed by 531

Abstract

The Gas Metal Arc Welding (GMAW) process is widely utilized in industrial production, requiring careful selection of appropriate procedures to ensure the highest quality. A key area of study closely related to GMAW quality is the control of process stability. This research presents [...] Read more.

The Gas Metal Arc Welding (GMAW) process is widely utilized in industrial production, requiring careful selection of appropriate procedures to ensure the highest quality. A key area of study closely related to GMAW quality is the control of process stability. This research presents a methodology for analyzing welding data to identify instability, thus enabling the development of a stability indicator. Our approach focuses on sensory fusion by integrating multiple sources of information, including sound signals, images, and current signals captured during the welding process. This work explores various configurations of variables to analyze the three primary transfer modes. Additionally, a comprehensive statistical analysis of the results obtained is conducted. Image processing techniques, sound analysis, and artificial intelligence methodologies are employed to enhance the analysis process. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Welded Structures)

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18 pages, 9611 KB

Open AccessArticle

Design, Preparation and Synergistic Optimization of Mechanical Properties and Thermal Neutron Shielding Performance of Mg-Dy-Sm-Zr Alloys

by Huabing Lu, Chengzhi Duan, Enci Niu, Xiyu Xu, Jia She, Jun Tan, Wei Zhang and Jianjun Mao

Crystals 2025, 15(10), 894; https://doi.org/10.3390/cryst15100894 - 15 Oct 2025

Viewed by 334

Abstract

Addressing the challenge of synergistically optimizing shielding performance and mechanical properties in nuclear radiation shielding materials, this study designed and prepared as-cast Mg-12Dy-xSm-0.4Zr (x = 1, 2, 3) alloys by incorporating rare earth elements Dy and Sm, which possess high thermal neutron absorption [...] Read more.

Addressing the challenge of synergistically optimizing shielding performance and mechanical properties in nuclear radiation shielding materials, this study designed and prepared as-cast Mg-12Dy-xSm-0.4Zr (x = 1, 2, 3) alloys by incorporating rare earth elements Dy and Sm, which possess high thermal neutron absorption cross-sections. The co-addition of Sm and Dy significantly refined the grains and promoted the precipitation of bone-like Mg₅(Sm,Dy) and Mg₄₁Sm₅ phases along grain boundaries. The alloys exhibited favorable mechanical properties, with ultimate tensile strength (UTS) reaching up to 194.6 MPa and elongation (EL) up to 10.9%. However, higher Sm content led to an increased amount of secondary phases at grain boundaries, resulting in stress concentration and a subsequent decline in both yield strength and elongation. Moreover, the combined addition of Dy and Sm markedly enhanced the thermal neutron shielding performance. Experimental results agreed well with Geant4 simulations, showing that both the neutron shielding rate and linear attenuation coefficient improved with increasing Sm content, demonstrating the positive role of Dy and Sm in neutron absorption. The developed alloy achieves simultaneous improvement in mechanical properties and neutron shielding capacity, providing valuable insights for the development of lightweight “function–structure integrated” radiation shielding materials for applications such as nuclear medicine and aerospace. Full article

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

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16 pages, 1751 KB

Open AccessArticle

Automated and Selective Product Removal for Lab-Scale Draft Tube Baffle Crystallizer Under Vacuum Operation

by Laura Marsollek, Merlin Hubmann, Kim Buchhorn and Norbert Kockmann

Crystals 2025, 15(10), 893; https://doi.org/10.3390/cryst15100893 - 15 Oct 2025

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Abstract

Continuous product removal in lab-scale vacuum applications poses significant challenges, particularly due to the risk of clogging in the product tube caused by the small tubing diameter relative to the particle size. This contribution addresses this problem by presenting an automatic gate system [...] Read more.

Continuous product removal in lab-scale vacuum applications poses significant challenges, particularly due to the risk of clogging in the product tube caused by the small tubing diameter relative to the particle size. This contribution addresses this problem by presenting an automatic gate system specifically designed for selective product removal within a Draft Tube Baffle Crystallizer (DTBC). In order to enable selective product removal, the classification behavior of the crystals in the DTBC was evaluated in experimental studies by determining the crystal size distributions in the product removal and in the fine grain dissolution. The influence of different stirring speeds and solid contents were considered for different product removal rates. The results indicated that sufficient classification occurs at stirring speeds of 600 rpm and a crystal content of ≥3 wt%. Under these conditions, more than 75% of the crystals in the product were larger than 210 μm from a sieve size range of 45 to 500 µm. During experiments, the automatic gate system allowed for blockage-free, continuous product removal for six hours per experiment and more than thirty hours in total, proving the reliability of the system. Although designed for down-scaling of the DTBC, this system can also be applied to other continuous-flow lab-scale applications. Full article

(This article belongs to the Section Crystal Engineering)

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21 pages, 4436 KB

Open AccessArticle

Activated Carbon–Geopolymer Composites: Influence of Particle Size and Content on CO₂ Adsorption and Mechanical and Thermal Properties

by Daniela Řimnáčová, Ivana Perná, Martina Novotná, Monika Šupová, Martina Nováková and Olga Bičáková

Crystals 2025, 15(10), 892; https://doi.org/10.3390/cryst15100892 - 15 Oct 2025

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Abstract

This study aims to develop and characterize innovative geopolymer composites by incorporating activated carbon into a geopolymer matrix to create a novel, effective sorption material suitable for non-dusty or medium-temperature environmental applications. Specifically, it examines the impact of using a single source of [...] Read more.

This study aims to develop and characterize innovative geopolymer composites by incorporating activated carbon into a geopolymer matrix to create a novel, effective sorption material suitable for non-dusty or medium-temperature environmental applications. Specifically, it examines the impact of using a single source of activated carbon, both in its original granular form and milled form, at two different loading levels for each. The research focuses on evaluating how these variations influence the textural, adsorption, mechanical, and thermal properties of the resulting geopolymer composites, with particular attention to strength and thermal stability under operational conditions. The CO₂ adsorption capacity of the composites measured at 25 °C and pressure up to 0.1 MPa varied from 48.8 to 60.0 mg.g⁻¹, with the highest performance observed at a lower content of the granular form, while commercial pure activated carbon reached 120.8 mg.g⁻¹. However, incorporation of a granular form negatively affected thermal stability (approximately 20 wt.% weight loss) and significantly reduced compressive strength (below 45 MPa) due to increased material inhomogeneity. Despite these limitations, both types of composites show promising potential for environmental applications. However, further optimization is required to balance sorption capacity, strength, and thermal stability. Full article

(This article belongs to the Section Macromolecular Crystals)

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19 pages, 5326 KB

Open AccessArticle

Preparation of Temperature-Responsive Janus Nanosheets and Their Application in Emulsions

by Yue Gao, Xuan Qi, Hao Yan, Dan Xue, Xuefeng Xu, Suixin He, Wei Xia and Junfeng Zhang

Crystals 2025, 15(10), 891; https://doi.org/10.3390/cryst15100891 - 15 Oct 2025

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Abstract

In this study, patch-structured C₈/CHO template microspheres were successfully synthesized through in situ reduction and sol–gel reactions, providing a reusable platform for subsequent modifications. Based on these templates, temperature-responsive PW₁₂O₄₀³⁻-PILs/PNIPAM Janus nanosheets were prepared via sequential [...] Read more.

In this study, patch-structured C₈/CHO template microspheres were successfully synthesized through in situ reduction and sol–gel reactions, providing a reusable platform for subsequent modifications. Based on these templates, temperature-responsive PW₁₂O₄₀³⁻-PILs/PNIPAM Janus nanosheets were prepared via sequential Schiff-base coupling and ATRP. Structural characterizations (XRD, SEM, TEM, FTIR, and TGA) confirmed successful functionalization and nanosheet formation. The PNIPAM moiety endowed the nanosheets with temperature responsiveness, while the incorporation of polymerized ionic liquids and phosphotungstate anions further enhanced amphiphilicity and dispersion stability. When applied as particulate emulsifiers in water/toluene systems, the Janus nanosheets formed stable Pickering emulsions at elevated temperatures and underwent reversible emulsification–demulsification upon temperature cycling. These findings demonstrate the potential of PW₁₂O₄₀³⁻-PILs/PNIPAM Janus nanosheets as smart emulsifiers for responsive separation and formulation technologies. Full article

(This article belongs to the Section Macromolecular Crystals)

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21 pages, 5374 KB

Open AccessArticle

Barium Carbonate Synthesized via Hydrolysis: Morphostructural Analysis and Photocatalytic Performance in Polymer and Geopolymer Matrices

by Adriana-Gabriela Schiopu, Maria-Ionela Popescu, Chaima Assamadi, Ecaterina Magdalena Modan, Sorin Georgian Moga, Denis Aurelian Negrea, Mihai Oproescu, Soumia Aboulhrouz, Hakima Aouad and Miruna-Adriana Ioța

Crystals 2025, 15(10), 890; https://doi.org/10.3390/cryst15100890 - 15 Oct 2025

Cited by 2 | Viewed by 453

Abstract

Barium carbonate (BaCO₃) nanoparticles were synthesized by a facile hydrolysis route using BaCl₂ and KOH in aqueous solution, with atmospheric CO₂ as the carbonate source, without external agents. Their structural and morphological properties were investigated by XRD, ATR-FTIR, SEM, [...] Read more.

Barium carbonate (BaCO₃) nanoparticles were synthesized by a facile hydrolysis route using BaCl₂ and KOH in aqueous solution, with atmospheric CO₂ as the carbonate source, without external agents. Their structural and morphological properties were investigated by XRD, ATR-FTIR, SEM, and BET, confirming the formation of a pure orthorhombic witherite phase with rod-like morphology and different surface specific areas. The crystallite size increased from 52 to 86 nm with higher precursor concentration and synthesis temperature, as predicted by a regression model correlating synthesis parameter with particle growth. When incorporated into polymer (PVC) and geopolymer (GP) matrices, BaCO₃ enhanced the photocatalytic degradation of methylene blue (MB) under solar light, with GP@Nano-BaCO₃ achieving a higher rate constant compared to PVC@Nano-BaCO₃. The results highlight that the synthesis strategy yields well-defined BaCO₃ nanoparticles with tunable structural features and promising photocatalytic potential when integrated in functional polymer matrices. Future work will address doping strategies and testing in real wastewater conditions. Overall, this synthesis strategy offers a reproducible and environmentally friendly route to BaCO₃ nanoparticles with potential applications in hybrid materials for visible light-driven environmental remediation. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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21 pages, 3712 KB

Open AccessArticle

LiCl@C-BMZIF Porous Composites: Synthesis, Structural Characterization, and the Effects of Carbonization Temperature and Salt Loading on Thermochemical Energy Storage

by Fuyao Zhang, Wenjing Wei, Quanrong Fang and Xianfeng Fan

Crystals 2025, 15(10), 889; https://doi.org/10.3390/cryst15100889 - 14 Oct 2025

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Abstract

To address the imbalance in energy supply and demand across different regions and seasons, the thermochemical conversion process was selected to efficiently utilize surplus energy. In the search for suitable novel materials, this study developed a porous matrix “in-salt” composite using a carbonized [...] Read more.

To address the imbalance in energy supply and demand across different regions and seasons, the thermochemical conversion process was selected to efficiently utilize surplus energy. In the search for suitable novel materials, this study developed a porous matrix “in-salt” composite using a carbonized metal-organic framework as the carrier and LiCl as the primary reactant. When exposed to water vapor, the innovative material enabled both adsorption and desorption of water vapor, leading to the release and storage of thermal energy, thereby achieving effective energy storage. Using Zn(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O as metal ion sources and 2-methylimidazole as the ligand, bimetallic zeolitic imidazolate frameworks (BMZIFs) were fabricated via the liquid-phase precipitation method. The composite specimen prepared at a carbonization temperature of 1000 °C with a 20% LiCl mass concentration exhibited the most promising thermal storage performance, achieving the highest capacity, with a final water loss of 53.56% and a stable water adsorption capacity of about 0.831 g·g⁻¹. Full article

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

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11 pages, 5008 KB

Open AccessArticle

Creation of Modified Aluminum Powders with Increased Reactivity for Energy Systems

by Ayagoz E. Bakkara, Ainur S. Khairullina, Aida B. Artykbayeva, Alua E. Maten, Aizhan O. Nugymanova, Anar O. Zhapekova and Bakhtiyar S. Sadykov

Crystals 2025, 15(10), 888; https://doi.org/10.3390/cryst15100888 - 14 Oct 2025

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Abstract

Aluminium plays a key role in developing modern energy technologies, from electrical systems to high-energy materials, providing a combination of functionality, economy, and reliability, but the oxide film on its particles reduces the effective reactivity. This work aims to increase the reactivity of [...] Read more.

Aluminium plays a key role in developing modern energy technologies, from electrical systems to high-energy materials, providing a combination of functionality, economy, and reliability, but the oxide film on its particles reduces the effective reactivity. This work aims to increase the reactivity of aluminum powder by mechanochemical treatment using modifiers. The materials used were aluminum powder of the ASD brand and graphite of the GL-1 brand. The experiment subjected aluminum powder to mechanochemical treatment (MCT) with different graphite contents. It was shown that MCT significantly increases active aluminum content in the powder due to partial destruction of the oxide film on its surface. In addition, morphological analyses confirm the destruction of the oxide, the graphite coating, and the appearance of lamellar structures measuring 0–58 µm. Thermal analysis shows that the primary exothermic peak shifts from 662.6 °C to 653.9 °C for Al + 10% graphite, and the heat released increases by 27%, which means lower activation energy and more complete oxidation. However, at 20% graphite, the thermal gain decreases, since carbon shields the metal areas. Thus, the optimal content is 10% graphite: at this ratio, the best thermochemical behavior of the powder is achieved. The data obtained indicate that the MCT of aluminum powder with graphite effectively increases its reactivity. The resulting aluminum powders with modified particle surfaces facilitate the development of new technologies for the creation of various high-energy solid propellant systems. For rocket engines, preference is given to solid rocket propellant (SRP), which is a mixture of substances (components) capable of burning in the absence of air, producing a large amount of gaseous working fluid heated to a high temperature, providing thrust. Full article

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

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22 pages, 4819 KB

Open AccessPerspective

Carbon Nanotube Production Pathways: A Review of Chemical Vapor Deposition and Electrochemical CO₂ Conversion, Such as C2CNT

by Gad Licht and Stuart Licht

Crystals 2025, 15(10), 887; https://doi.org/10.3390/cryst15100887 - 14 Oct 2025

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Abstract

Graphene Nano-Carbons (GNCs) have a huge potential, but current production methods limit their exploration and use. Many GNCs will be explored here with a focus on CNTs (Carbon NanoTubes) (which have some of the highest strengths of any known material, conductivity, EMF absorptivity, [...] Read more.

Graphene Nano-Carbons (GNCs) have a huge potential, but current production methods limit their exploration and use. Many GNCs will be explored here with a focus on CNTs (Carbon NanoTubes) (which have some of the highest strengths of any known material, conductivity, EMF absorptivity, and many other useful properties. Manufacturing them abundantly, inexpensively, and in eco-friendly ways remains a significant challenge. Two CNT/GNCs production methods are compared and reviewed. Traditional Chemical Vapor Deposition (CVD) production heats organic reactants with metal catalysts to form GNC/CNTs. As of now, the CVD CNT production has been limited by the high-energy costs, costs per weight comparable to precious metals, and a high CO₂-footprint. C2CNT is an electrochemical methodology that overcomes the constraints of CVD, while producing high-quality CNT/GNCs. C2CNT is a molten carbonate CO₂-electrolysis that makes GNCs. The C2CNT process also selectively produces a wider variety of CNTs (including helical, magnetic, and doped) and GNCs with higher product specificity than CVD by fine-tuning electrolysis parameters. The wide variety of CNTs/GNCs that can be produced by each of these methods is reviewed and discussed. The goal of this perspective is to compare GNC production methods. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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15 pages, 3607 KB

Open AccessArticle

Photo-Responsive Brominated Hydrogen-Bonded Liquid Crystals

by Christian Anders, Tejal Nirgude, Ahmed F. Darweesh and Mohamed Alaasar

Crystals 2025, 15(10), 886; https://doi.org/10.3390/cryst15100886 - 14 Oct 2025

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Abstract

This study reports on the preparation and comprehensive characterisation of new brominated hydrogen-bonded liquid crystalline (HBLC) materials. Two distinct series of supramolecular complexes were prepared by hydrogen-bond formation between 3-bromo-4-pentyloxybenzoic acid as the proton donor and non-fluorinated and fluorinated azopyridines with variable terminal [...] Read more.

This study reports on the preparation and comprehensive characterisation of new brominated hydrogen-bonded liquid crystalline (HBLC) materials. Two distinct series of supramolecular complexes were prepared by hydrogen-bond formation between 3-bromo-4-pentyloxybenzoic acid as the proton donor and non-fluorinated and fluorinated azopyridines with variable terminal chains as proton acceptors. The successful formation of a hydrogen bond was confirmed by FTIR spectroscopy. The impact of alkyl chain length and fluorination on the mesomorphic properties of the HBLCs was systematically investigated. The molecular self-assembly was thoroughly examined using polarised optical microscopy (POM) and differential scanning calorimetry (DSC), revealing the presence of smectic C (SmC), smectic A (SmA), and nematic (N) phases, with thermal stability being highly dependent on the molecular architecture. Notably, the introduction of fluorine atoms significantly influenced the phase transition temperatures and the overall mesophase range. Using bromine as a lateral substituent induces the formation of SmC phases in these HBLCs, a feature absent in their non-brominated analogues. Further structural insights were obtained through X-ray diffraction (XRD) investigations, confirming the nature of the observed LC phases. Additionally, the photo-responsive characteristics of these HBLCs were explored via UV-Vis spectroscopy, demonstrating their ability to undergo reversible photoisomerisation upon light irradiation. These findings underscore the critical role of precise molecular design in tailoring the properties of HBLCs for potential applications such as optical storage devices. Full article

(This article belongs to the Special Issue Thermotropic Liquid Crystals as Novel Functional Materials)

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10 pages, 3119 KB

Open AccessArticle

Printable Silicone-Based Emulsions as Promising Candidates for Electrically Conductive Glass-Ceramic Composites

by Annalaura Zilio and Enrico Bernardo

Crystals 2025, 15(10), 885; https://doi.org/10.3390/cryst15100885 - 14 Oct 2025

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Abstract

The Na₂O-SrO-SiO₂ system shows promise in the development of glasses that can be transformed into electrically conductive glass ceramics. The conventional processing of such materials usually involves the synthesis of a parent glass, followed by a complex devitrification treatment. This [...] Read more.

The Na₂O-SrO-SiO₂ system shows promise in the development of glasses that can be transformed into electrically conductive glass ceramics. The conventional processing of such materials usually involves the synthesis of a parent glass, followed by a complex devitrification treatment. This study proposes a simplified approach based on the use of preceramic polymers, namely silicone resins combined with oxide fillers. These systems yield silicate-based ceramics through direct heat treatment, replicating the phase assembly of traditional glass ceramics with no need for prior glass melting. A printable formulation was developed by mixing a silicone resin with an acrylate-based photocurable resin, sodium nitrate and strontium carbonate. The resulting ‘suspension-emulsion’ was later shaped into monolithic components using digital light processing. After pyrolysis in nitrogen atmosphere, the components transformed into SrSiO₃ crystals embedded in a composite matrix, in turn composed of glass and turbostratic carbon (the latter specifically offered by the silicone polymer). This combination of crystalline silicates and carbon resulted in measurable electrical conductivity. This study confirms that silicone-derived systems can serve as effective precursors for conductive glass-ceramic analogues, providing an alternative to conventional methods with single-step processing. This approach enables structural shaping through 3D printing and the development of functional properties suitable for electronic or electrochemical applications. Full article

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

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15 pages, 6721 KB

Open AccessArticle

Mechanical Behaviors of Copper Nanoparticle Superlattices: Role of Lattice Structure

by Jianjun Bian and Liang Yang

Crystals 2025, 15(10), 884; https://doi.org/10.3390/cryst15100884 - 13 Oct 2025

Viewed by 363

Abstract

Nanoparticle superlattices, periodic assemblies of nanoscale building blocks, offer opportunities to tailor mechanical behavior through controlled lattice geometry and interparticle interactions. Here, classical molecular dynamics simulations were performed to investigate the compressive responses of copper nanoparticle superlattices with face-centered cubic (FCC), hexagonal close-packed [...] Read more.

Nanoparticle superlattices, periodic assemblies of nanoscale building blocks, offer opportunities to tailor mechanical behavior through controlled lattice geometry and interparticle interactions. Here, classical molecular dynamics simulations were performed to investigate the compressive responses of copper nanoparticle superlattices with face-centered cubic (FCC), hexagonal close-packed (HCP), body-centered cubic (BCC), and simple cubic (SC) arrangements, as well as disordered assemblies. The flow stresses span 0.5–1.5 GPa. Among the studied configurations, the FCC and HCP superlattices exhibit the highest strengths (~1.5 GPa), followed by the disordered assembly (~1.0 GPa) and the SC structure (~0.8 GPa), while the BCC superlattice exhibits the lowest strength (~0.5 GPa), characterized by pronounced stress drops and recoveries resulting from interfacial sliding. Atomic-scale analyses reveal that plastic deformation is governed by two coupled geometric factors: (i) the number of interparticle contact patches, controlling the density of dislocation sources, and (ii) their orientation relative to the loading axis, which dictates stress transmission and slip activation. A combined parameter integrating particle coordination number and contact orientation is proposed to rationalize the structure-dependent strength, providing mechanistic insight into the deformation physics of metallic nanoparticle assemblies. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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21 pages, 3707 KB

Open AccessArticle

Synthesis, Crystal Structure and Optical Properties of Novel 1,10-Phenanthroline Derivatives Containing 2,6-Diisopropylphenoxy Substituents

by Martin Tsvetkov, Rumen Lyapchev, Mihail Kolarski, Bernd Morgenstern and Joana Zaharieva

Crystals 2025, 15(10), 883; https://doi.org/10.3390/cryst15100883 - 13 Oct 2025

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Abstract

Two phenanthroline derivatives, 2-(2,6-diisopropylphenoxy)-9-phenyl-1,10-phenanthroline and 2,9-bis(2,6-diisopropylphenoxy)-1,10-phenanthroline, were synthesized. The unsymmetrical derivative was obtained in high yield through a sequence combining Suzuki coupling and nucleophilic substitution. The crystal structures of both compounds were determined by single-crystal X-ray diffraction and examined by Hirshfeld surface analysis, [...] Read more.

Two phenanthroline derivatives, 2-(2,6-diisopropylphenoxy)-9-phenyl-1,10-phenanthroline and 2,9-bis(2,6-diisopropylphenoxy)-1,10-phenanthroline, were synthesized. The unsymmetrical derivative was obtained in high yield through a sequence combining Suzuki coupling and nucleophilic substitution. The crystal structures of both compounds were determined by single-crystal X-ray diffraction and examined by Hirshfeld surface analysis, which outlined the main intermolecular interactions responsible for the packing. The optical properties were studied by UV–Vis absorption and fluorescence spectroscopy in different solvents. The unsymmetrical compound showed stronger intramolecular charge transfer and more pronounced solvatochromism, while the symmetrical analog had a higher fluorescence quantum yield and longer excited-state lifetime. These results demonstrate the role of substitution symmetry in controlling molecular organization and photophysical properties of phenanthroline derivatives, with relevance to sensing and optoelectronic applications. Full article

(This article belongs to the Section Organic Crystalline Materials)

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15 pages, 3572 KB

Open AccessArticle

Effects of Nd₂Fe₁₄B Powder Particle Size and Content on Microstructure and Properties of Nd₂Fe₁₄B_p/2024Al Composites

by Tao Qin, Qin Yang, Jincheng Yu, Bowen Fan, Ping Guo and Chenglong Ding

Crystals 2025, 15(10), 882; https://doi.org/10.3390/cryst15100882 - 13 Oct 2025

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Abstract

In this article, a Nd₂Fe₁₄B_p/2024Al composite was prepared using high-energy ball milling, magnetic field cold isostatic pressing, and microwave sintering. The influence of powder particle size on microstructure and mechanical properties was discussed. The experimental results demonstrated [...] Read more.

In this article, a Nd₂Fe₁₄B_p/2024Al composite was prepared using high-energy ball milling, magnetic field cold isostatic pressing, and microwave sintering. The influence of powder particle size on microstructure and mechanical properties was discussed. The experimental results demonstrated that a ball milling duration of 10 h yielded powders with an average particle size of 5 μm, resulting in a refined and homogeneous microstructure, with a hardness value of 115 HV. Additionally, the densification process of the microwave-sintered sample was analyzed. When the sintering temperature was 490 °C, in-depth analysis was conducted on the effect of Nd₂Fe₁₄B addition on the microstructure and properties of the composite. The results showed that when the addition of Nd₂Fe₁₄B was 15 wt.%, the microstructure of the composite was uniform with fewer pores, and the Nd₂Fe₁₄B phase was evenly distributed on the matrix. At the same time, the compactness, microhardness, yield strength, and compressive strength of the composite also reached their optimal values, which were 94.3%, 136 HV, 190.5 MPa, and 248.9 MPa, respectively. When the addition of Nd₂Fe₁₄B reached 20 wt.%, the magnetic properties of the composite were slightly better than those of 15 wt.% Nd₂Fe₁₄B addition. However, based on the goal of preparing a high-magnetic and high-performance aluminum-based composite, considering the microstructure, mechanical properties, and magnetic properties comprehensively, it is believed that 15 wt.% is the optimal addition amount of Nd₂Fe₁₄B. Full article

(This article belongs to the Special Issue Microstructural Characterization and Property Analysis of Alloys)

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15 pages, 8005 KB

Open AccessArticle

Effect of the Activator B(OCH₃)₃ on the Microstructure and Mechanical Properties of Cu-Mn-Al Alloy Coating via CMT Cladding

by Jin Peng, Shihua Xie, Junhai Xia, Xingxing Wang, Zenglei Ni, Pei Wang and Nannan Chen

Crystals 2025, 15(10), 881; https://doi.org/10.3390/cryst15100881 - 13 Oct 2025

Cited by 1 | Viewed by 323

Abstract

This study investigates the fabrication of a Cu-Mn-Al alloy coating on 27SiMn steel using Cold Metal Transfer (CMT) technology with an innovative Ar-B(OCH₃)₃ mixed shielding gas, focusing on the effect of the gas flow rate (5–20 L/min). The addition of [...] Read more.

This study investigates the fabrication of a Cu-Mn-Al alloy coating on 27SiMn steel using Cold Metal Transfer (CMT) technology with an innovative Ar-B(OCH₃)₃ mixed shielding gas, focusing on the effect of the gas flow rate (5–20 L/min). The addition of B(OCH₃)₃ was found to significantly enhance process stability by improving molten pool wettability, resulting in a wider cladding layer (6.565 mm) and smaller wetting angles compared to pure Ar. Macro-morphology analysis identified 10 L/min as the optimal flow rate for achieving a uniform and defect-free coating, while deviations led to oxidation (at low flow) or spatter and turbulence (at high flow). Microstructural characterization revealed that the flow rate critically governs phase evolution, with the primary κI phase transforming from dendritic/granular to petal-like/rod-like morphologies. At higher flow rates (≥15 L/min), increased stirring promoted Fe dilution from the substrate, leading to the formation of Fe-rich intermetallic compounds and distinct spherical Fe phases. Consequently, the cladding layer obtained at 10 L/min exhibited balanced and superior properties, achieving a maximum shear strength of 303.22 MPa and optimal corrosion resistance with a minimum corrosion rate of 0.02935 mm/y. All shear fractures occurred within the cladding layer, demonstrating superior interfacial bonding strength and ductile fracture characteristics. This work provides a systematic guideline for optimizing shielding gas parameters in the CMT cladding of high-performance Cu-Mn-Al alloy coatings. Full article

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18 pages, 2751 KB

Open AccessArticle

Assessment of the Influence of Chemical Composition, Atomic Distribution, and Grain Boundaries on Heat Transfer in Refractory High-Entropy Alloys Hf–Nb–Ta–Zr Based on Atomistic Simulation

by Rita I. Babicheva, Arseny M. Kazakov and Elena A. Korznikova

Crystals 2025, 15(10), 880; https://doi.org/10.3390/cryst15100880 - 13 Oct 2025

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Abstract

This work investigates the influence of chemical composition, grain boundary (GB) type, and atomic distribution on the thermal conductivity of Hf–Nb–Ta–Zr refractory high-entropy alloys (RHEAs) via atomistic simulations. Three compositions—equiatomic HfNbTaZr (M1), Hf₁₀Nb₄₀Ta₁₀Zr₄₀ (M2), and Hf [...] Read more.

This work investigates the influence of chemical composition, grain boundary (GB) type, and atomic distribution on the thermal conductivity of Hf–Nb–Ta–Zr refractory high-entropy alloys (RHEAs) via atomistic simulations. Three compositions—equiatomic HfNbTaZr (M1), Hf₁₀Nb₄₀Ta₁₀Zr₄₀ (M2), and Hf₄₀Nb₁₀Ta₄₀Zr₁₀ (M3)—were studied in single-crystalline and bicrystalline models containing Σ3 or Σ5 GBs. The effect of chemical short-range order (SRO) and GB segregation was probed by comparing results for non-relaxed structures with those obtained for corresponding materials relaxed using combined Monte Carlo/molecular dynamics (MC/MD) simulation. Material relaxation is accompanied by the formation of coherent nanoclusters (NbTa in M1, Nb or Zr in M2, Hf or Ta in M3) and Hf/Zr segregation to GBs. In single crystals, SRO reduces thermal conductivity by up to ~2.7% (e.g., from 3.66 to 3.56 W/m·K in M1), which is explained by the phonon scattering effect from matrix–cluster interfaces, densely distributed in the structures. In contrast, in certain bicrystals, the combined effects of GB healing and intragranular cluster coarsening lead to a 6.9% increase in thermal conductivity (from 4.59 to 4.93 W/m·K), despite the presence of high-energy Σ5 GBs. These results demonstrate that the interplay between SRO, GB segregation, and microstructural evolution governs phonon transport in RHEAs, revealing a counterintuitive pathway to enhance thermal conductivity through controlled atomic redistribution. Full article

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

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