Crystals

11 pages, 1217 KiB

Open AccessArticle

Spatial Anisotropy of Photoelasticity Determined by Path Difference in Ba₃TaGa₃Si₂O₁₄Crystals

by Natalia Demyanyshyn, Oleh Buryy, Bohdan Mytsyk, Pavlo Solomenchuk, Oleksandr Lishchuk and Anatoliy Andrushchak

Crystals 2025, 15(8), 708; https://doi.org/10.3390/cryst15080708 (registering DOI) - 31 Jul 2025

Abstract

The elastic and photoelastic coefficients of Ba₃TaGa₃Si₂O₁₄(BTGS) crystals were determined by the quantum–mechanical calculation technique. Based on these data, extreme piezo-optic surfaces π′°_km were constructed, which describe the change in the path difference [...] Read more.

The elastic and photoelastic coefficients of Ba₃TaGa₃Si₂O₁₄(BTGS) crystals were determined by the quantum–mechanical calculation technique. Based on these data, extreme piezo-optic surfaces π′°_km were constructed, which describe the change in the path difference in light beams in the crystal under the influence of mechanical stress. The results for BTGS crystals are compared with the ones for other crystals of the langasite group (La₃Ga₅SiO₁₄, Ca₃Ga₂Ge₄O₁₄, Ca₃TaGa₃Si₂O₁₄and Ca₃NbGa₃Si₂O₁₄). The global maxima of the π′°_km surfaces for BTGS crystals significantly exceed the ones for the other crystals mentioned above and, accordingly, BTGS crystals can be suitable for use in polarization-optic light modulators and devices based on them. The acousto-optic efficiency of BTGS crystals was evaluated. The correlations between the magnitude of the piezo- and elasto-optic coefficients and the parameters of the unit cell of the studied crystals were determined. Full article

(This article belongs to the Special Issue Design and Synthesis of Functional Crystal Materials)

19 pages, 1866 KiB

Open AccessArticle

Lithium Lanthanum Titanate (LLTO) Solid Electrolyte with High Ionic Conductivity and Excellent Mechanical Properties Prepared by Aerodynamic Levitation Rapid Solidification

by Yidong Hu, Fan Yang, Jianguo Li and Qiaodan Hu

Crystals 2025, 15(8), 707; https://doi.org/10.3390/cryst15080707 (registering DOI) - 31 Jul 2025

Abstract

Lithium lanthanum titanate (LLTO) is a promising solid electrolyte for all-solid-state lithium-ion batteries (ASSLIBs), and its total conductivity is dramatically influenced by the ceramic microstructure. Here we report a novel aerodynamic levitation rapid solidification method to prepare dense LLTO ceramics with a dendrite-like [...] Read more.

Lithium lanthanum titanate (LLTO) is a promising solid electrolyte for all-solid-state lithium-ion batteries (ASSLIBs), and its total conductivity is dramatically influenced by the ceramic microstructure. Here we report a novel aerodynamic levitation rapid solidification method to prepare dense LLTO ceramics with a dendrite-like microstructure, which can be hardly obtained by conventional sintering. At optimal nominal lithium content and cooling rate, the solidified LLTO ceramic achieved a high total conductivity of 2.5 × 10⁻⁴ S·cm⁻¹ at room temperature, along with excellent mechanical properties such as a high Young’s modulus of 240 GPa and a high hardness of 16.7 GPa. Results from this work suggest that aerodynamic levitation rapid solidification is an effective processing method to manipulate the microstructure of LLTO ceramics to minimize the GBs’ contribution to the total conductivity, which may be expanded to prepare other oxide-type lithium electrolytes. Full article

16 pages, 5622 KiB

Open AccessArticle

Molecular Dynamics Simulations on the Deformation Behaviors and Mechanical Properties of the γ/γ′ Superalloy with Different Phase Volume Fractions

by Xinmao Qin, Wanjun Yan, Yilong Liang and Fei Li

Crystals 2025, 15(8), 706; https://doi.org/10.3390/cryst15080706 (registering DOI) - 31 Jul 2025

Abstract

Based on molecular dynamics simulation, we conducted a comprehensive study on the tensile behaviors and properties of the

γ

(Ni)/

γ^{'}

(Ni₃Al) superalloy with varying

γ^{'}

(Ni₃Al) phase volume fractions (

V (γ^{'}))

under high-temperature, [...] Read more.

Based on molecular dynamics simulation, we conducted a comprehensive study on the tensile behaviors and properties of the

γ

(Ni)/

γ^{'}

(Ni₃Al) superalloy with varying

γ^{'}

(Ni₃Al) phase volume fractions (

V (γ^{'}))

under high-temperature, high-strain-rate service environments. Our investigation revealed that the tensile behavior of the superalloy depends critically on the

V (γ^{'})

. When the

V (γ^{'})

increased from 13.5 to 67%, the system’s tensile strength exhibited a non-monotonic response, peaking at

V (γ^{'})

= 40.3% before progressively decreasing. Conversely, the maximum uniform plastic strain decreased linearly and significantly when

V (γ^{'})

increased. These results establish an atomistically informed framework that elucidates the composition–microstructure–property relationships in

γ

(Ni)/

γ^{'}

(Ni₃Al) superalloys, specifically addressing how

V (γ^{'})

governs variations in deformation mechanisms and mechanical performance. Furthermore, this work provides quantitative design paradigm for optimizing

γ^{'}

(Ni₃Al) precipitate architecture and compositional tuning in the Ni-based

γ

(Ni)/

γ^{'}

(Ni₃Al) superalloy. Full article

(This article belongs to the Special Issue Advances in High-Performance Alloys)

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15 pages, 930 KiB

Open AccessArticle

The Effect of Nematic Liquid Crystal on the Performance of Dye-Sensitized Solar Cells

by Paweł Szubert and Stanisław A. Różański

Crystals 2025, 15(8), 705; https://doi.org/10.3390/cryst15080705 (registering DOI) - 31 Jul 2025

Abstract

The motivation for increasing the efficiency of renewable energy sources is the basic problem of ongoing research. Currently, intensive research is underway in technology based on the use of dye-sensitized solar cells (DSSCs). The aim of this work is to investigate the effect [...] Read more.

The motivation for increasing the efficiency of renewable energy sources is the basic problem of ongoing research. Currently, intensive research is underway in technology based on the use of dye-sensitized solar cells (DSSCs). The aim of this work is to investigate the effect of modifying the iodide electrolyte with liquid crystals (LCs) known for the self-organization of molecules into specific mesophases. The current–voltage (I-V) and power–voltage (P-V) characteristics were determined for the ruthenium-based dyes N3, Z907, and N719 to investigate the influence of their structure and concentration on the efficiency of DSSCs. The addition of a nematic LC of 4-n-pentyl-4-cyanobiphenyl (5CB) to the iodide electrolyte influences the I-V and P-V characteristics. A modification of the I-V characteristics was found, especially a change in the values of short circuit current (I_SC) and open circuit voltage (V_OC). The conversion efficiency for cells with modified electrolyte shows a complex dependence that first increases and then decreases with increasing LC concentration. It may be caused by the orientational interaction of LC molecules with the titanium dioxide (TiO₂) layer on the photoanode. A too high concentration of LC may lead to a reduction in total ionic conductivity due to the insulating effect of the elongated polar molecules. Full article

(This article belongs to the Collection Liquid Crystals and Their Applications)

16 pages, 6426 KiB

Open AccessArticle

Manganese-Rich Chromite in Myanmar Jadeite Jade: A Critical Source of Chromium and Manganese and Its Role in Coloration

by Yu Zhang, Guanghai Shi and Jiabao Wen

Crystals 2025, 15(8), 704; https://doi.org/10.3390/cryst15080704 (registering DOI) - 31 Jul 2025

Abstract

Color is a primary determinant of the value of jadeite jade, but the petrological provenance of the chromogenic elements of jadeite jade remains uncertain. The characteristics of the associated chromite in Myanmar jadeite jade were systematically investigated through a series of tests, including [...] Read more.

Color is a primary determinant of the value of jadeite jade, but the petrological provenance of the chromogenic elements of jadeite jade remains uncertain. The characteristics of the associated chromite in Myanmar jadeite jade were systematically investigated through a series of tests, including polarized microscopy, microarea X-ray fluorescence spectroscopy (micro-XRF) mapping, electron probe microanalysis (EPMA), and backscattered electron (BSE) imaging. The results demonstrate that the chromite composition in Myanmar jadeite jade is characterized by a high concentration of Cr₂O₃ (46.18–67.11 wt.%), along with a notable abundance of MnO (1.68–9.13 wt.%) compared with the chromite from the adjacent Myitkyina peridotite. The diffusion of chromium (Cr) and manganese (Mn) in jadeite jade is accomplished by accompanying the metamorphic pathway of Mn-rich chromite → kosmochlor → chromian jadeite → jadeite. In the subsequent phase of jadeite jade formation, the chromium-rich omphacite veins generated by the fluid enriched in Ca and Mg along the fissures of kosmochlor and chromian jadeite play a role in the physical diffusion of Cr and Mn. The emergence of the lavender hue in jadeite is contingent upon the presence of a relatively high concentration of Mn (approximately 100–1000 ppmw) and the simultaneous absence of Cr, which would otherwise serve as a more effective chromophore (no Cr or up to a dozen ppmw). The distinctive Mn-rich chromite represents the primary origin of the chromogenic element Cr (green) and, perhaps more notably, an overlooked provider of Mn (lavender) in Myanmar jadeite jade. Full article

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13 pages, 2073 KiB

Open AccessArticle

Dynamic Nucleation in Zr-2.5Nb During Reduced-Gravity Electromagnetic Levitation Experiments

by Gwendolyn P. Bracker, Stephan Schneider, Sarah Nell, Mitja Beckers, Markus Mohr and Robert W. Hyers

Crystals 2025, 15(8), 703; https://doi.org/10.3390/cryst15080703 (registering DOI) - 31 Jul 2025

Abstract

Levitation techniques reduce the available heterogeneous nucleation sites and provide stable access to deeply undercooled melts. However, some samples have repeatably demonstrated that, in the presence of strong stirring, solidification may be induced at moderate, sub-critical undercoolings. Dynamic nucleation is a mechanism by [...] Read more.

Levitation techniques reduce the available heterogeneous nucleation sites and provide stable access to deeply undercooled melts. However, some samples have repeatably demonstrated that, in the presence of strong stirring, solidification may be induced at moderate, sub-critical undercoolings. Dynamic nucleation is a mechanism by which solidification may be induced through flow effects within a sub-critically undercooled melt. In this mechanism, collapsing cavities within the melt produce very high-pressure shocks, which shift the local melting temperature. In these regions of locally shifted melt temperatures, thermodynamic conditions enable nuclei to grow and trigger solidification of the full sample. By deepening the local undercooling, dynamic nucleation enables solidification to occur in conditions where classical nucleation does not. Dynamic nucleation has been observed in several zirconium and zirconium-based samples in the Electromagnetic Levitator onboard the International Space Station (ISS-EML). The experiments presented here address conditions in which a zirconium sample alloyed with 2.5 atomic percent niobium spontaneously solidifies during electromagnetic levitation experiments with strong melt stirring. In these experimental conditions, classical nucleation predicts the sample to remain liquid. This solidification behavior is consistent with the solidification behavior observed in prior experiments on pure zirconium. Full article

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14 pages, 4194 KiB

Open AccessArticle

Crystal Structure of Anthranilate Phosphoribosyltransferase from Methanocaldococcus jannaschii

by Jung-Min Choi

Crystals 2025, 15(8), 702; https://doi.org/10.3390/cryst15080702 (registering DOI) - 31 Jul 2025

Abstract

Tryptophan is synthesized in microorganisms via a five-step enzymatic pathway originating from chorismate, which is a product of the shikimate pathway. As a biosynthetic precursor to a wide range of high-value compounds such as indole-3-acetic acid, indigo, indirubin, and violacein, this pathway has [...] Read more.

Tryptophan is synthesized in microorganisms via a five-step enzymatic pathway originating from chorismate, which is a product of the shikimate pathway. As a biosynthetic precursor to a wide range of high-value compounds such as indole-3-acetic acid, indigo, indirubin, and violacein, this pathway has been a central target for metabolic engineering to enhance microbial production. Anthranilate phosphoribosyltransferase (AnPRT) catalyzes the second step of the pathway by transferring a phosphoribosyl group from PRPP to anthranilate, forming phosphoribosyl anthranilate (PRA). AnPRT, the sole member of class IV phosphoribosyltransferases, adopts a unique fold and functions as a homodimer. While the structural basis of AnPRT activity has been elucidated in several organisms, thermostable variants remain underexplored despite their relevance for high-temperature bioprocessing. In this study, the crystal structure of AnPRT from the thermophilic archaeon Methanocaldococcus jannaschii (MjAnPRT) was determined at a 2.16 Å resolution. The enzyme exhibits a conserved dimeric architecture and key catalytic motifs. Comparative structural analysis with mesophilic and hyper thermophilic homologs revealed that MjAnPRT possesses enhanced local stability in catalytically important regions and strengthened inter-subunit interactions. These features likely contribute to its thermostability and provide a valuable framework for the rational design of robust AnPRTs for industrial and synthetic biology applications. Full article

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

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22 pages, 9293 KiB

Open AccessArticle

Thermal Stability of the Ultra-Fine-Grained Structure and Mechanical Properties of AlSi7MgCu0.5 Alloy Processed by Equal Channel Angular Pressing at Room Temperature

by Miloš Matvija, Martin Fujda, Ondrej Milkovič, Marek Vojtko and Katarína Gáborová

Crystals 2025, 15(8), 701; https://doi.org/10.3390/cryst15080701 (registering DOI) - 31 Jul 2025

Abstract

Understanding the limitations of cold-formed aluminum alloys in practice applications is essential, particularly due to the risk of substructural changes and a reduction in strength when exposed to elevated temperatures. In this study, the thermal stability of the ultra-fine-grained (UFG) structure formed by [...] Read more.

Understanding the limitations of cold-formed aluminum alloys in practice applications is essential, particularly due to the risk of substructural changes and a reduction in strength when exposed to elevated temperatures. In this study, the thermal stability of the ultra-fine-grained (UFG) structure formed by equal channel angular pressing (ECAP) at room temperature and the mechanical properties of the AlSi7MgCu0.5 alloy were investigated. Prior to ECAP, the plasticity of the as-cast alloy was enhanced by a heat treatment consisting of solution annealing, quenching, and artificial aging to achieve an overaged state. Four repetitive passes via ECAP route A resulted in the homogenization of eutectic Si particles within the α-solid solution, the formation of ultra-fine grains and/or subgrains with high dislocation density, and a significant improvement in alloy strength due to strain hardening. The main objective of this work was to assess the microstructural and mechanical stability of the alloy after post-ECAP annealing in the temperature range of 373–573 K. The UFG microstructure was found to be thermally stable up to 523 K, above which notable grain and/or subgrain coarsening occurred as a result of discontinuous recrystallization of the solid solution. Mechanical properties remained stable up to 423 K; above this temperature, a considerable decrease in strength and a simultaneous increase in ductility were observed. Synchrotron radiation X-ray diffraction (XRD) was employed to analyze the phase composition and crystallographic characteristics, while transmission electron microscopy (TEM) was used to investigate substructural evolution. Mechanical properties were evaluated through tensile testing, impact toughness testing, and hardness measurements. Full article

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

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14 pages, 1605 KiB

Open AccessArticle

Supramolecular Switching by Substituent Tuning: A Crystal Engineering Study of 2-Amino- and 2,3-Diamino-5-Halogenopyridines

by Irina S. Konovalova and Guido J. Reiss

Crystals 2025, 15(8), 700; https://doi.org/10.3390/cryst15080700 (registering DOI) - 31 Jul 2025

Abstract

The crystal structures of the 2-amino-5-halogenopyridines (halogen = Cl (1), Br (2)) and 2,3-diamino-5-halogenopyridines (halogen = Cl (3), Br (4)) were compared with respect to their intermolecular interactions. An ab-initio-based method for evaluating the interaction [...] Read more.

The crystal structures of the 2-amino-5-halogenopyridines (halogen = Cl (1), Br (2)) and 2,3-diamino-5-halogenopyridines (halogen = Cl (3), Br (4)) were compared with respect to their intermolecular interactions. An ab-initio-based method for evaluating the interaction energies between molecules was employed to estimate the driving forces of crystal formation. As a result, regularities in crystal structure organization were identified. For compounds 1 and 2, a dimeric building unit is formed by two N–H…N_pyr hydrogen bonds. These dimers are further connected to neighboring units by C–H…π, C–H…N, N…X (X = Cl, Br), and non-specific interactions. The aforementioned intermolecular interactions give rise to layered structures that are similar but not isotypical. No significant contributions from π–π or N–H…N(H₂) interactions are observed in 1 and 2. The structures of 3 and 4 are isotypical and crystallize in the non-centrosymmetric space group P2₁2₁2₁. The most important intermolecular interactions are N–H…N_pyr, N–H…N(H₂), and stacking interactions. These interactions lead to identical columnar-layered structures in both 3 and 4. No significant contributions from halogen bonds of the type N…X (X = Cl, Br) are found in 3 and 4. Full article

(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals (2nd Edition))

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28 pages, 3272 KiB

Open AccessReview

Research Advancements in High-Temperature Constitutive Models of Metallic Materials

by Fengjuan Ding, Tengjiao Hong, Fulong Dong and Dong Huang

Crystals 2025, 15(8), 699; https://doi.org/10.3390/cryst15080699 (registering DOI) - 31 Jul 2025

Abstract

The constitutive model is widely employed to characterize the rheological properties of metallic materials under high-temperature conditions. It is typically derived from a series of high-temperature tests conducted at varying deformation temperatures, strain rates, and strains, including hot stretching, hot compression, separated Hopkinson [...] Read more.

The constitutive model is widely employed to characterize the rheological properties of metallic materials under high-temperature conditions. It is typically derived from a series of high-temperature tests conducted at varying deformation temperatures, strain rates, and strains, including hot stretching, hot compression, separated Hopkinson pressure bar testing, and hot torsion. The original experimental data used for establishing the constitutive model serves as the foundation for developing phenomenological models such as Arrhenius and Johnson–Cook models, as well as physical-based models like Zerilli–Armstrong or machine learning-based constitutive models. The resulting constitutive equations are integrated into finite element analysis software such as Abaqus, Ansys, and Deform to create custom programs that predict the distributions of stress, strain rate, and temperature in materials during processes such as cutting, stamping, forging, and others. By adhering to these methodologies, we can optimize parameters related to metal processing technology; this helps to prevent forming defects while minimizing the waste of consumables and reducing costs. This study provides a comprehensive overview of commonly utilized experimental equipment and methods for developing constitutive models. It discusses various types of constitutive models along with their modifications and applications. Additionally, it reviews recent research advancements in this field while anticipating future trends concerning the development of constitutive models for high-temperature deformation processes involving metallic materials. Full article

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12 pages, 7989 KiB

Open AccessArticle

Microstructures and Magnetic Properties of Rare-Earth-Free Co-Zr-Mo-B Alloys

by Tetsuji Saito and Masaru Itakura

Crystals 2025, 15(8), 698; https://doi.org/10.3390/cryst15080698 (registering DOI) - 31 Jul 2025

Abstract

The growing demand for rare-earth magnets has raised concerns over their price and the country’s risk of depleting the supply of rare-earth elements. These severe concerns have led to the study of rare-earth-free magnets that do not rely on rare-earth elements. Co-Zr-Mo-B alloys, [...] Read more.

The growing demand for rare-earth magnets has raised concerns over their price and the country’s risk of depleting the supply of rare-earth elements. These severe concerns have led to the study of rare-earth-free magnets that do not rely on rare-earth elements. Co-Zr-Mo-B alloys, one of the prospective candidates for rare-earth-free magnets, were produced by the melt-spinning technique and subsequent annealing. It was found that a small substitution of Mo for Zr in the Co-Zr-B alloys increased coercivity. The Co-Zr-Mo-B alloy with a Mo content of 2 at% showed a high coercivity of 6.2 kOe with a remanence of 40 emu/g. SEM studies showed that the annealed Co-Zr-Mo-B alloys had fine, uniform grains with an average diameter of about 0.6 μm. Further studies using STEM demonstrated that the ferromagnetic phase in the annealed Co-Zr-Mo-B alloys with high coercivity was composed of the Co₅Zr phase and the long-period stacking ordered (LPSO) phase. That is, the fine grains observed in the SEM studies were found to be ferromagnetic dendrites containing numerous twin boundaries of the Co₅Zr phase and its derived LPSO phase. Therefore, the high coercivity of the Co-Zr-Mo-B alloys can be attributed to the presence of ferromagnetic crystals of Co₅Zr and the derived LPSO phase. Full article

(This article belongs to the Special Issue Innovations in Magnetic Composites: Synthesis to Application)

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18 pages, 2612 KiB

Open AccessArticle

Pressure Response of Crystalline Fluoranthene Probed by Raman Spectroscopy

by Olga Karabinaki, Stylianos Papastylianos, Nayra Machín Padrón, Antonios Hatzidimitriou, Dimitrios Christofilos and John Arvanitidis

Crystals 2025, 15(8), 697; https://doi.org/10.3390/cryst15080697 (registering DOI) - 30 Jul 2025

Abstract

The pressure response and structural stability of fluoranthene crystals up to 8 GPa are investigated using Raman spectroscopy. The vast majority of the Raman peaks upshift with pressure, either sublinearly (intermolecular modes) or quasilinearly (intramolecular modes), reflecting the bond hardening upon volume contraction. [...] Read more.

The pressure response and structural stability of fluoranthene crystals up to 8 GPa are investigated using Raman spectroscopy. The vast majority of the Raman peaks upshift with pressure, either sublinearly (intermolecular modes) or quasilinearly (intramolecular modes), reflecting the bond hardening upon volume contraction. The frequency shifts, accompanied by intensity redistribution among the Raman peaks, are by far larger for the former than those for the latter vibrations, compatible with their nature: weak intermolecular van der Waals interactions and strong intramolecular covalent bonds. For pressures higher than 2 GPa, changes in the linear pressure coefficients of the Raman peak frequencies, mainly towards lower values, are observed. These are more pronounced for intermolecular and C–H stretching vibrations. For P > 4.7 GPa, the pressure coefficients are further reduced, while all the observed pressure-induced changes are fully reversible upon pressure release. These changes may be interpreted either as two structural transitions at ~2 and ~4.7 GPa or as a single, but sluggish, structural phase transition in the pressure range 2–4.7 GPa, featuring the reorientation and different stacking of the molecules. From the high-pressure Raman data in the low-pressure phase, a bulk modulus of ~7 GPa at ambient pressure is estimated for solid fluoranthene. Full article

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Graphical abstract

14 pages, 1862 KiB

Open AccessReview

Update of Natural Compounds in Transthyretin Amyloidosis, Years 2020–2025

by Carlo Marotta, Lidia Ciccone and Susanna Nencetti

Crystals 2025, 15(8), 696; https://doi.org/10.3390/cryst15080696 - 30 Jul 2025

Abstract

Transthyretin amyloidosis (ATTR) is a disease caused by the deposition of transthyretin-derived fibrils in the body. Despite extensive research conducted over the years, there are currently only four drugs available in clinical use to treat this condition, two of which are repurposed drugs [...] Read more.

Transthyretin amyloidosis (ATTR) is a disease caused by the deposition of transthyretin-derived fibrils in the body. Despite extensive research conducted over the years, there are currently only four drugs available in clinical use to treat this condition, two of which are repurposed drugs used off-label. However, these treatments present several limitations; therefore, there is an urgent need for new therapeutic options. In this context, dietary supplements containing natural compounds capable of stabilizing the transthyretin (TTR) protein could represent a promising approach to contrast the disease progression, potentially supporting the therapeutic effects of the aforementioned drugs. In light of this, the present review highlights and analyzes the natural compounds that have most recently been reported in the literature as TTR stabilizers. In particular, the studies elucidating the potential of these compounds in the treatment of ATTR, along with the available crystallographic data explaining their binding mode to TTR, are reported. Overall, although the use of natural compounds as supplements shows promise in managing ATTR, further research is still needed to explore its feasibility and confirm its effectiveness. Hopefully, this work will help shed light on these issues and serve as a useful starting point for the development of new strategies to treat this disease. Full article

(This article belongs to the Collection Feature Papers in Biomolecular Crystals)

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18 pages, 7751 KiB

Open AccessArticle

Microanalysis-Based Simulation of Heterogeneous Dispersoid Distribution in an Al Alloy After the Homogenization Stage

by Nicolás García Arango, Roman Schuster, Rainer Abart and Erwin Povoden-Karadeniz

Crystals 2025, 15(8), 695; https://doi.org/10.3390/cryst15080695 (registering DOI) - 30 Jul 2025

Abstract

We simulate the dispersoid distribution within the Al matrix grains of an aluminum 6082 alloy by combining finite difference cell modeling with mean-field precipitation simulations. The results demonstrate that the initial as-cast microstructure and the heating rate during the ramp-up to the isothermal [...] Read more.

We simulate the dispersoid distribution within the Al matrix grains of an aluminum 6082 alloy by combining finite difference cell modeling with mean-field precipitation simulations. The results demonstrate that the initial as-cast microstructure and the heating rate during the ramp-up to the isothermal homogenization temperature are the most important factors governing the dispersoid particle distribution. The simulation results are validated by Electron Probe Microanalysis (EPMA) and Optical Microscopy on experimental run products. The results indicate that dispersoids can only achieve uniform distribution throughout the grain when the heating rate to the homogenization temperature is sufficiently slow. Full article

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

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10 pages, 1727 KiB

Open AccessArticle

Chemical–Mechanical Super-Polishing of Al₂O₃ (0001) Wafer for Epitaxial Purposes

by Chih-Hao Lee and Chih-Hong Lee

Crystals 2025, 15(8), 694; https://doi.org/10.3390/cryst15080694 - 30 Jul 2025

Abstract

A super-polishing procedure was performed on the Al₂O₃ (0001) surface for epitaxial purposes. The roughness of the final polished surface was measured to be 0.16 nm using atomic force microscopy and X-ray reflectivity techniques. After heat treatment at 130 °C, [...] Read more.

A super-polishing procedure was performed on the Al₂O₃ (0001) surface for epitaxial purposes. The roughness of the final polished surface was measured to be 0.16 nm using atomic force microscopy and X-ray reflectivity techniques. After heat treatment at 130 °C, results from low-energy electron diffraction and Auger energy spectroscopy indicated that the top surface was well ordered and clean, rendering it suitable for epitaxial growth. The successful growth of a GaN thin film on an Al₂O₃ (0001) substrate was confirmed by the hk-circle scan in XRD and the presence of a sharp peak in the rocking curve of the GaN (0002) Bragg peak. These findings indicate that the top surface of the substrate is conducive to epitaxial growth. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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10 pages, 1855 KiB

Open AccessArticle

TCAD Design and Optimization of In_0.20Ga_0.80N/In_0.35Ga_0.65N Quantum-Dot Intermediate-Band Solar Cells

by Salaheddine Amezzoug, Haddou El Ghazi and Walid Belaid

Crystals 2025, 15(8), 693; https://doi.org/10.3390/cryst15080693 - 30 Jul 2025

Abstract

Intermediate-band photovoltaics promise single-junction efficiencies that exceed the Shockley and Queisser limit, yet viable material platforms and device geometries remain under debate. Here, we perform comprehensive two-dimensional device-scale simulations using Silvaco Atlas TCAD to analyze p-i-n In_0.20Ga_0.80N solar cells [...] Read more.

Intermediate-band photovoltaics promise single-junction efficiencies that exceed the Shockley and Queisser limit, yet viable material platforms and device geometries remain under debate. Here, we perform comprehensive two-dimensional device-scale simulations using Silvaco Atlas TCAD to analyze p-i-n In_0.20Ga_0.80N solar cells in which the intermediate band is supplied by In_0.35Ga_0.65N quantum dots located inside the intrinsic layer. Quantum-dot diameters from 1 nm to 10 nm and areal densities up to 116 dots per period are evaluated under AM 1.5G, one-sun illumination at 300 K. The baseline pn junction achieves a simulated power-conversion efficiency of 33.9%. The incorporation of a single 1 nm quantum-dot layer dramatically increases efficiency to 48.1%, driven by a 35% enhancement in short-circuit current density while maintaining open-circuit voltage stability. Further increases in dot density continue to boost current but with diminishing benefit; the highest efficiency recorded, 49.4% at 116 dots, is only 1.4 percentage points above the 40-dot configuration. The improvements originate from two-step sub-band-gap absorption mediated by the quantum dots and from enhanced carrier collection in a widened depletion region. These results define a practical design window centred on approximately 1 nm dots and about 40 dots per period, balancing substantial efficiency gains with manageable structural complexity and providing concrete targets for epitaxial implementation. Full article

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

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14 pages, 1657 KiB

Open AccessArticle

How Do the Surroundings of the C-NO₂ Fragment Affect the Mechanical Sensitivity of Trinitroaromatic Molecules? Evidence from Crystal Structures and Ab Initio Calculations

by Danijela S. Kretić, Aleksandra B. Đunović, Dragan B. Ninković and Dušan Ž. Veljković

Crystals 2025, 15(8), 692; https://doi.org/10.3390/cryst15080692 - 30 Jul 2025

Abstract

The dissociation of the C-NO₂ bond is the initial step in the process of the detonation of nitroaromatic explosives. The strength of the C-NO₂ bond is significantly influenced by the relative position of the nitro group with respect to the aromatic [...] Read more.

The dissociation of the C-NO₂ bond is the initial step in the process of the detonation of nitroaromatic explosives. The strength of the C-NO₂ bond is significantly influenced by the relative position of the nitro group with respect to the aromatic ring plane since the planar arrangement enables the delocalization of electron density, which strengthens this bond. In this study, we have combined a statistical analysis of geometrical parameters extracted from crystal structures of trinitroaromatic molecules with ab initio calculations of non-covalent index plots and Wiberg bond index values for selected trinitroaromatic molecules to elucidate the influence of nearby substituents on the relative position of nitro groups with respect to the aromatic ring plane. The results of the analysis showed that neighboring substituents have a significant impact on the geometry of nitro groups. The results also showed that this influence arises from the repulsive interaction of voluminous substituents, attractive non-covalent contacts, and the electronic effects of substituents. Full article

(This article belongs to the Section Organic Crystalline Materials)

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19 pages, 4231 KiB

Open AccessArticle

Design and Synthesis of a New Photoluminescent 2D Coordination Polymer Employing a Ligand Derived from Quinoline and Pyridine

by Andrzej Kochel, Małgorzata Hołyńska, Aneta Jezierska and Jarosław J. Panek

Crystals 2025, 15(8), 691; https://doi.org/10.3390/cryst15080691 - 30 Jul 2025

Abstract

Application of organic ligand 2-(3-ethyl-pyrazin-2-yl)quinoline-4-carboxylate with N/O donor atoms enabled solvothermal synthesis of a 2D Cu(II) coordination polymer, {Cu(L)BF₄}_n (L = deprotonated 2-(3-ethyl-pyrazin-2-yl)quinoline-4-carboxylate). Both the ligand and its coordination polymer have been characterized. The condensed ring system of the applied [...] Read more.

Application of organic ligand 2-(3-ethyl-pyrazin-2-yl)quinoline-4-carboxylate with N/O donor atoms enabled solvothermal synthesis of a 2D Cu(II) coordination polymer, {Cu(L)BF₄}_n (L = deprotonated 2-(3-ethyl-pyrazin-2-yl)quinoline-4-carboxylate). Both the ligand and its coordination polymer have been characterized. The condensed ring system of the applied ligand promotes the formation of coordination polymers rather than mononuclear species. The obtained 2D coordination polymer is photoluminescent with bathochromic/hypsochromic shifts in ligand absorption bands leading to a single absorption band at 465 nm. Density Functional Theory was employed to provide a theoretical description of the possible conformational changes within the ligand, with emphasis on the difference between the ligand conformation in its hydrochloride salt and in the polymer. Two models of polymer fragments were constructed to describe the electronic structure and non-covalent interactions. The Quantum Theory of Atoms in Molecules (QTAIM) was applied for this purpose. Using the obtained results, we were able to develop potential energy profiles for various conformations of the ligand. For the set of the studied systems, we detected non-covalent interactions, which are responsible for the spatial conformation. Concerning the models of polymers, electron spin density distribution has been visualized and discussed. Full article

(This article belongs to the Special Issue Research Progress of Photoluminescent Materials)

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22 pages, 4237 KiB

Open AccessArticle

Gone with the Wind—Adducts of Volatile Pyridine Derivatives and Copper(II) Acetylacetonate

by Luca Mensing, Tim Schäfer, Marcus Layh and Marian Hebenbrock

Crystals 2025, 15(8), 690; https://doi.org/10.3390/cryst15080690 - 29 Jul 2025

Abstract

The investigation of adducts of weakly coordinating pyridine ligands with copper acetylacetonate is more arduous in the presence of volatile pyridine derivatives. The present study reports the synthesis of new adducts, including those with volatile ligands. Furthermore, the formation of one-dimensional coordination polymers [...] Read more.

The investigation of adducts of weakly coordinating pyridine ligands with copper acetylacetonate is more arduous in the presence of volatile pyridine derivatives. The present study reports the synthesis of new adducts, including those with volatile ligands. Furthermore, the formation of one-dimensional coordination polymers is observed when bidentate ligands are used. The synthesis and characterization of the adduct formed by pyridine is particularly noteworthy, which despite its simplicity has not yet been structurally elucidated. A total of four pentacoordinate complexes, one oligomer and two coordination polymers are synthesized and discussed in this study. The obtained structures of the complexes complement the spectrum of known adducts due to the substituents on the pyridines, and allow conclusions to be drawn about the cause of the different structures based on the electronic properties of the substituents. Furthermore, intermolecular interactions are discussed using Hirshfeld surface analysis and attributed to the pyridine derivatives present. Full article

(This article belongs to the Special Issue Synthesis, Crystal Structures and Hirshfeld Surface Analysis of Coordination Compounds (3rd Edition))

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