Crystals

17 pages, 48738 KB

Open AccessArticle

Experimental Characterization and Finite Element Simulation of the Microstructure and Mechanical Properties in 0.2% Sc-Modified A242 Aluminum Alloy

by Mahmoud A. Alzahrani, Obaidullah Alfahmi, Essam B. Moustafa and Ahmed O. Mosleh

Crystals 2026, 16(6), 388; https://doi.org/10.3390/cryst16060388 (registering DOI) - 12 Jun 2026

Abstract

Scandium (Sc) is well recognized as a potent grain refiner, yet optimizing its addition amount in the Al-Cu-Mg-Ni-Fe (A242) system remains a longstanding challenge, critically important for material performance in high-temperature automotive and aerospace applications. The present work, therefore, presents a study of [...] Read more.

Scandium (Sc) is well recognized as a potent grain refiner, yet optimizing its addition amount in the Al-Cu-Mg-Ni-Fe (A242) system remains a longstanding challenge, critically important for material performance in high-temperature automotive and aerospace applications. The present work, therefore, presents a study of low-Sc modified A242 alloys, demonstrating that 0.2 wt.% Sc microalloying of the system has a pronounced effect on its solidification-driven microstructural evolution, improving the high-temperature formability of the alloy over a 20–200 °C temperature range. The study demonstrates that this addition triggers a dramatic columnar-to-equiaxed grain transition, reducing the average grain size by 90.8% (from 400 ± 100 μm to 37 ± 10 μm) and fragmenting the brittle, continuous intermetallic network into a highly uniform architecture. Uniaxial compression testing revealed that, while the as-cast solid-solution alloy slightly reduces room-temperature strength due to solute trapping, it delivers an exceptional 142% increase in strain-to-failure at 200 °C (exceeding 0.8 mm) compared to the base alloy. This significant enhancement in ductility is driven by thermally stable Al₃Sc dispersoids that exert Zener pinning pressure, halting thermal grain coarsening and activating superplastic deformation mechanisms. These findings support the development of advanced thermoforming applications, with the finite element (FE) model predicting process improvements that enhance manufacturing efficiency. This work presents a validation and simulation-ready material framework that substantiates the viability of low-Sc-modified A242 alloys for such operations. Full article

(This article belongs to the Special Issue State of the Art of Crystalline Metals and Alloys)

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19 pages, 2531 KB

Open AccessArticle

Yield Prediction Model for Ingot Samples Based on Machine Learning and Data Augmentation

by Renlong Jie, Fan Yang, Shouzhi Xi, Sanqi Tang and Wanqi Jie

Crystals 2026, 16(6), 387; https://doi.org/10.3390/cryst16060387 (registering DOI) - 12 Jun 2026

Abstract

The preparation of high-performance cadmium zinc telluride (CZT) radiation detector materials requires efficient ingot-level quality assessment before full downstream wafer testing. This study proposes a machine learning framework that predicts the product-level yield of test wafers from IV and double-sided spectral measurements of [...] Read more.

The preparation of high-performance cadmium zinc telluride (CZT) radiation detector materials requires efficient ingot-level quality assessment before full downstream wafer testing. This study proposes a machine learning framework that predicts the product-level yield of test wafers from IV and double-sided spectral measurements of a limited number of standardized evaluation wafers from the same ingot. To address the small number of ingots and wafer-level variability, ingot-level aggregate, A/B-side consistency, threshold-ratio, and distributional features were combined with intra-ingot bootstrap augmentation. Among the evaluated regression models, Random Forest achieved the best held-out test performance under a leakage-safe protocol, with an MSE of 0.021, an MAE of 0.125, and a Pearson correlation coefficient of 0.646; XGBoost showed comparable performance, with an MSE of 0.023, an MAE of 0.128, and a Pearson correlation coefficient of 0.601. In a top-22% screening experiment, the average true yield of ingots selected by Random Forest and XGBoost reached 63.71% and 60.40%, respectively, exceeding the empirical Rule_IV_Abs baseline of 59.08%. These results indicate that the proposed framework can provide useful ranking and prioritization support for early CZT ingot screening, while remaining a decision-support tool rather than a replacement for wafer-level inspection. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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22 pages, 3410 KB

Open AccessReview

Crystallization-Based Technologies for Microplastic Removal from Wastewater: Mechanisms, Advances, and Future Perspectives

by Bhavya Tiwari, Nikita Joshi, Raj Kumar Arya, D. Giribabu and George D. Verros

Crystals 2026, 16(6), 386; https://doi.org/10.3390/cryst16060386 - 12 Jun 2026

Abstract

Persistent microplastics contaminate wastewater systems and pose significant environmental and human health risks due to their small size, buoyancy, persistence, and diverse physicochemical properties, which reduce the effectiveness of conventional treatment technologies. Freeze crystallization, indirect freeze crystallization, eutectic freeze crystallization, and ice-templated separation [...] Read more.

Persistent microplastics contaminate wastewater systems and pose significant environmental and human health risks due to their small size, buoyancy, persistence, and diverse physicochemical properties, which reduce the effectiveness of conventional treatment technologies. Freeze crystallization, indirect freeze crystallization, eutectic freeze crystallization, and ice-templated separation have emerged as promising long-term technologies for microplastic removal. Particle rejection at the solid–liquid interface, heterogeneous ice nucleation, brine channel formation, and particle entrapment within advancing ice fronts are key crystallization mechanisms governing microplastic separation. Microplastics can adhere to or nucleate growing ice crystals, according to lab and field research. These interactions influence crystal growth kinetics and ice structure formation. Indirect freeze crystallization (IFC) and related chemical-free crystallization systems offer lower energy requirements and improved scalability. Crystallization processes concentrate microplastics for downstream treatment, may connect with photochemical or oxidative degradation at ice interfaces, and are useful in cold areas or low-temperature industrial streams. Despite these advances, several challenges remain, including freezing rate, salinity, particle size distribution, and surface weathering, which are difficult to control. Integrating crystallization into wastewater treatment systems is also difficult. This review covers the latest advances in microplastic–ice interactions, crystallization engineering, and freeze-based separation technologies. It also highlights major knowledge gaps and suggests future research to use crystallization to remove microplastics from wastewater in a sustainable, scalable, and energy-efficient manner. Full article

(This article belongs to the Section Industrial Crystallization)

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15 pages, 13457 KB

Open AccessArticle

Phase Transformation and Hydrogen Embrittlement Assessment in Pre-Strained 316L Austenitic Stainless Steel Sheets

by Stavroula Maritsa, Maciej Szczerba, Magdalena Bieda, Joanna Wojewoda-Budka, Theodore Steriotis, Christos Tampaxis and Anna D. Zervaki

Crystals 2026, 16(6), 385; https://doi.org/10.3390/cryst16060385 - 11 Jun 2026

Abstract

Marine transportation and storage of liquid hydrogen (LH2) has gained increasing interest, while potential LH2 membrane-type tanks could utilize 316L corrugated austenitic stainless-steel sheets. The corrugation process results in a strain-induced martensitic transformation in the material, introducing rapid diffusion pathways for hydrogen atoms [...] Read more.

Marine transportation and storage of liquid hydrogen (LH2) has gained increasing interest, while potential LH2 membrane-type tanks could utilize 316L corrugated austenitic stainless-steel sheets. The corrugation process results in a strain-induced martensitic transformation in the material, introducing rapid diffusion pathways for hydrogen atoms and promoting the formation of hydrogen-trapping sites that alter hydrogen transport and reduce the material’s resistance to hydrogen embrittlement. In this study, 316L sheets were subjected to different levels of uniaxial pre-strain (10, 20, 30, and 40%) with two different strain-rates, to replicate the varying degrees of pre-deformation caused by the corrugation. Microstructural analysis using Electron Backscatter Diffraction (EBSD) (Thermo Fisher Scientific, Waltham, MA, USA) and X-Ray Diffraction (XRD) (Bruker, Billerica, MA, USA) combined with quantitative phase analysis using the Rietveld Method on XRD data, provided valuable insights into the induced phase transformations. Cathodic hydrogen charging method was implemented on as-received and pre-strained material, followed by slow strain rate tensile testing (SSRT) and thermal desorption spectroscopy (TDS) to examine the hydrogen effect on each condition. Experimental results indicated that although 316L exhibits considerable phase stability, it undergoes strain-induced phase transformation resulting in a significant amount of martensite, reaching 5% in the 40% pre-strained condition. Pre-deformation increased hydrogen embrittlement, as evidenced by fractographic analysis which indicated a Relative Reduction of Area (RRA) of 0.83, and by increased hydrogen uptake. These findings contribute to a better understanding of phase transformations and the role of hydrogen in austenitic stainless steels. Full article

(This article belongs to the Special Issue From Processing to Performance: Microstructure Engineering in Advanced Metallic Alloys)

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18 pages, 13703 KB

Open AccessArticle

Investigation of Mechanical and Tribological Behaviour of SiC- and Carbon Nanotube-Reinforced Aluminium Matrix Hybrid Nanocomposites

by Arpita Chatterjee, Samjukta Sinha, Prabhat Das, Saikat Paul, Abhishek Ghosh and Manojit Ghosh

Crystals 2026, 16(6), 384; https://doi.org/10.3390/cryst16060384 - 9 Jun 2026

Abstract

Enhancing the mechanical performance of aluminium-based materials remains a critical challenge for their application in demanding environments. In this context, aluminium-based hybrid nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs) and nano-sized silicon carbide (nSiC) have been developed to overcome inherent limitations of pure [...] Read more.

Enhancing the mechanical performance of aluminium-based materials remains a critical challenge for their application in demanding environments. In this context, aluminium-based hybrid nanocomposites reinforced with multi-walled carbon nanotubes (MWCNTs) and nano-sized silicon carbide (nSiC) have been developed to overcome inherent limitations of pure aluminium, such as relatively low hardness, limited compressive strength and poor wear resistance. The composites were fabricated via powder metallurgy by incorporating a fixed 1 wt.% MWCNT content along with varying nSiC additions in the range of 0–4 wt.%, enabling a systematic evaluation of the effect of hybrid reinforcement on the overall material properties. Compared to pure aluminium, the composites exhibited significant improvements in mechanical and tribological properties, with the Al–1 wt.% MWCNT–4 wt.% nSiC composition showing the highest enhancement, achieving increases of ~149% in hardness and ~45% in compressive strength. Microstructural analysis revealed strong matrix–reinforcement bonding, notable grain refinement, and a largely uniform reinforcement distribution, with minor agglomeration at higher nSiC content. The hybrid nanocomposites also demonstrated superior wear resistance, while fractography indicated a transition from ductile fracture in pure aluminium to a mixed intergranular–transgranular mode, promoting effective load transfer and improved performance. Full article

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

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22 pages, 5048 KB

Open AccessArticle

Pressure-Induced Indirect-to-Direct Band Gap Transition and Tunable Deep-UV Response in CsCaF₃ Perovskite

by Serkan Güldal

Crystals 2026, 16(6), 383; https://doi.org/10.3390/cryst16060383 - 9 Jun 2026

Abstract

This study presents a comprehensive first-principles investigation of the structural, elastic, electronic, and optical behavior of cubic CsCaF₃ under hydrostatic pressure. The material is confirmed to be a stable Pm-3m fluoride perovskite, with a lattice constant of

4.496 Å

and a [...] Read more.

This study presents a comprehensive first-principles investigation of the structural, elastic, electronic, and optical behavior of cubic CsCaF₃ under hydrostatic pressure. The material is confirmed to be a stable Pm-3m fluoride perovskite, with a lattice constant of

4.496 Å

and a tolerance factor of

0.902

. At ambient conditions, CsCaF₃ exhibits high intrinsic stiffness (

C_{11} = 107.88 G P a

,

B = 53.07 G P a

,

G = 29.16 G P a

,

E = 73.94 G P a

) and maintains mechanical stability while becoming progressively stiffer under compression. The electronic structure reveals a wide indirect band gap of

7.1 e V

that broadens to

8.43 e V

and transforms into a direct gap at elevated pressures. Optical calculations show strong transparency in the visible range, with a low refractive index (

1.58

) and reflectivity (

~ 5 %

), and a deep-UV absorption edge near

6 e V

. Pressure enhances these features, increasing the refractive index to 1.66 and the maximum reflectivity to 45.87% at

24 G P a

. The plasmon resonance also displays pronounced tunability, blue-shifting from

29.56

to

30.79 e V

with a fourfold rise in intensity. Analysis of the effective-electron number further indicates pressure-driven redistribution of spectral weight within the UV region. Together, these findings demonstrate that CsCaF₃ combines robust structural stability with highly pressure-tunable optical and plasmonic responses, positioning it as a promising candidate for deep-UV optoelectronics, photonic coatings, and pressure-responsive optical technologies. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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13 pages, 3037 KB

Open AccessArticle

Research on the Electrical Properties and Microstructural Characteristics of ZnO Varistors Under Impulse Current

by Yong Wang, Jie Zhang, Jun Xiong, Junxiang Liu, Lu Zhu and Yongxia Han

Crystals 2026, 16(6), 382; https://doi.org/10.3390/cryst16060382 - 8 Jun 2026

Abstract

Zinc oxide (ZnO) varistors are a core component of surge arresters; their failure can directly affect the secure and reliable operation of power equipment. Therefore, this paper conducts an impulse degradation test on ZnO varistors, combining electrical and microstructural tests to systematically explore [...] Read more.

Zinc oxide (ZnO) varistors are a core component of surge arresters; their failure can directly affect the secure and reliable operation of power equipment. Therefore, this paper conducts an impulse degradation test on ZnO varistors, combining electrical and microstructural tests to systematically explore the intrinsic correlation mechanism between the electrical properties and microstructural characteristics. Test results show that this type of ZnO varistor is susceptible to side-glaze surface flashover under an impulse current with a waveform of 8/20 μs and an amplitude of 27 kA, and the discharge branches exhibit an extension from the negative electrode towards the positive electrode. Moreover, surface flashover causes the formation of local conductive channels in the side glaze layer, resulting in a significant drop in the direct-current (DC) reference voltage U_1mA. However, the residual voltage U_10kA increases slightly with an increase in the number of impulse groups, with a change in amplitude of less than 1.5%. Additionally, the microstructural testing reveals that the impulse currents cause the bismuth (Bi) element in ZnO grains to precipitate and form more Bi-rich phases at the grain boundaries. This results in an increase in the thickness of the grain boundary layer, which is negatively correlated with the U_1mA. Meanwhile, the grain morphology and size distribution of brand-new samples, samples with different degrees of degradation, and samples with side-glaze surface flashover damage are not significantly different. This is consistent with the fact that the change range of the residual voltage U_10kA during impulse degradation is very small. This test phenomenon indicates that the failure of this type of ZnO varistor to withstand an impulse current with a waveform of 8/20 μs and an amplitude of 27 kA is mainly due to changes in the volt-ampere properties of the small-current regions caused by ion migration within the grain boundary layer. This research provides an experimental basis and theoretical support for improving the impulse withstand capacity of ZnO varistors in their design. Full article

(This article belongs to the Section Crystal Engineering)

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18 pages, 20181 KB

Open AccessArticle

Al-Bearing Scorodite (Scorodite—Mansfieldite Series) from Hemerdon Ball Mine, Plympton, Tavistock District, Devon, United Kingdom: Single-Crystal X-Ray Diffraction, Chemistry and Vibrational Spectroscopy

by Iuliu Bobos, J. Theo Kloprogge, Paula Brandão, João Rocha, Rui Vilarinho and Joaquim Agostinho Moreira

Crystals 2026, 16(6), 381; https://doi.org/10.3390/cryst16060381 - 6 Jun 2026

Abstract

The Al-bearing scorodite from the Hemerdon Ball Mine (HBM) was studied using electron microscopy and microprobe analysis, single-crystal X-ray diffraction, infrared, and Raman spectroscopy. The crystal chemistry formula of Al-bearing scorodite is expressed as Fe³⁺_0.87Al³⁺_0.16(As_0.97O [...] Read more.

The Al-bearing scorodite from the Hemerdon Ball Mine (HBM) was studied using electron microscopy and microprobe analysis, single-crystal X-ray diffraction, infrared, and Raman spectroscopy. The crystal chemistry formula of Al-bearing scorodite is expressed as Fe³⁺_0.87Al³⁺_0.16(As_0.97O₄)·H₂O. The calculated d-spacings and unit-cell parameters of Al-bearing scorodite are slightly affected by the substitution of Al for Fe in the octahedral sites. The Al-bearing scorodite HBM crystalizes in the Pbca space group with the following unit-cell lattice parameters: a = 8.92882(14) Å; b = 10.02217(14) Å; c = 10.30525(15) Å; V(Å) = 922.18(2) and Z = 8. The lattice structure becomes slightly distorted by the formation of the Fe,Al-OH octahedron, which leads to a compression of the newly formed octahedron along the a* ^ b* direction and an expansion of the Fe-OH octahedron along the c* direction. The incorporation of Al³⁺ has a strong effect on the tilting angle of the Fe,Al-OH octahedron in the b* ^ c* crystallographic direction. The refined structure suggests that Al³⁺ occupies the octahedral sites alongside Fe³⁺, leading to a distortion of the Fe,Al-OH octahedron. Infrared and Raman spectroscopy exhibit a doublet at 820 and 800 cm⁻¹, and at 810 and 800 cm⁻¹ ascribed to the Fe,Al-O-OAsO₃ group. The 799–800 cm⁻¹ Raman region is assigned to the Fe–O–As group (at 798 and 803 cm⁻¹), whereas the 810–814 cm⁻¹ region is ascribed to a band resulting from the AsO₄³⁻ [υ₁ (A₁) symmetric stretching vibrational modes], indicative of the Fe,Al–OH–As group in both Al-bearing scorodite and mansfieldite. Full article

(This article belongs to the Special Issue Crystal Structure and Characterization of Minerals and Related Nanomaterials)

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29 pages, 3650 KB

Open AccessReview

Research Progress and Prospects of Inorganic Rare Earth Luminescence Thermometry Technology

by Junyuan Liang, Zibo Chen, Tingting Cao, Peixuan Chen, Caiyuan Wen, Qinhua Jiang, Jiajun Feng, Lianfen Chen and Xiang Li

Crystals 2026, 16(6), 380; https://doi.org/10.3390/cryst16060380 - 5 Jun 2026

Abstract

Temperature is a physical quantity that represents the degree of heat or cold of an object and has significant application value across various fields. Traditional contact temperature measurement technologies, such as thermocouples and infrared thermometers, suffer from limitations like poor environmental adaptability and [...] Read more.

Temperature is a physical quantity that represents the degree of heat or cold of an object and has significant application value across various fields. Traditional contact temperature measurement technologies, such as thermocouples and infrared thermometers, suffer from limitations like poor environmental adaptability and low spatial resolution, which makes it difficult to meet the temperature measurement requirements for micro-/nano-devices and extreme environments. In recent years, non-contact optical temperature measurement technology based on the luminescence characteristics of rare earth ions has garnered widespread attention due to its high sensitivity, strong interference resistance, and good environmental adaptability. In addition to inorganic luminescent materials, lanthanide-based molecular and coordination-complex thermometers have also become an important branch of this field; however, this paper focuses on inorganic rare earth luminescence thermometry. This paper provides a systematic review of the mechanisms of temperature measurement using rare earth ion luminescence, including single-energy-level luminescence intensity measurement and luminescence intensity ratio measurement based on thermally coupled levels (TCLs) and non-thermally coupled levels (NTCLs). It analyzes the principles of various technologies, performance parameters (such as absolute sensitivity S_a, relative sensitivity S_r, and temperature resolution δT), and their application progress in fields such as biomedical imaging, high-temperature aerospace environments, and the integration of micro-/nano-devices. Special attention is paid to emerging research directions, including Stark sublevel engineering for enhanced sensitivity, negative thermal expansion (NTE) host design for anti-thermal quenching, multi-modal collaborative thermometry, and artificial intelligence (AI)-assisted material design and data processing. The article also discusses the challenges currently faced by the technology, such as high-temperature fluorescence quenching and signal interference, and looks forward to future development directions, including artificial intelligence-assisted material design and multi-modal cooperative temperature measurement, aiming to provide a reference for the research and application of rare earth luminescence temperature sensing technology. Full article

(This article belongs to the Topic High Performance Ceramic Functional Materials)

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24 pages, 4132 KB

Open AccessArticle

Copper Complexes of Some Polyphenols Extracted from Taraxacum officinale and Their Immobilization on Sericite-Based Hybrid Supports

by Florentina Monica Raduly, Valentin Raditoiu, Alina Raditoiu, Iuliana Raut, Radu Claudiu Fierascu, Cristian-Andi Nicolae and Rusandica Stoica

Crystals 2026, 16(6), 379; https://doi.org/10.3390/cryst16060379 - 5 Jun 2026

Abstract

Polyphenolic compounds extracted from Taraxacum officinale (dandelion) were used as natural chelating ligands to synthesize copper–polyphenol complexes, which were subsequently immobilized on sericite to obtain hybrid organic–inorganic materials. The complexes were prepared under controlled pH and temperature conditions, yielding structures with different Cu–polyphenol [...] Read more.

Polyphenolic compounds extracted from Taraxacum officinale (dandelion) were used as natural chelating ligands to synthesize copper–polyphenol complexes, which were subsequently immobilized on sericite to obtain hybrid organic–inorganic materials. The complexes were prepared under controlled pH and temperature conditions, yielding structures with different Cu–polyphenol ratios. Structural characterization confirmed the formation of Cu(II)–polyphenol chelates, partial reduction to Cu(I) species at higher pH values, and the deposition of mixed Cu₂O/CuO phases on the layered sericite substrate. Copper–polyphenol superstructures, copper nanoparticles, and copper oxide crystallites were heterogeneously distributed depending on synthesis conditions and metal–ligand ratios. The hybrid materials exhibited modified optical properties, combining the intrinsic reflectance of sericite with UV absorption from polyphenols and copper species. When incorporated into an emulsion matrix, the materials showed promising UV-screening performance, with SPF-equivalent values ranging from 7 to 33 depending on concentration. Antimicrobial evaluation demonstrated that copper–polyphenol complexes displayed enhanced activity against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Candida albicans compared to the natural extract, while sericite-supported hybrids retained selective efficacy, particularly against Gram-positive bacteria and C. albicans. These results indicate the potential of dandelion-derived copper complexes and their sericite hybrids as multifunctional bioactive agents for cosmetic dermatology applications. Full article

(This article belongs to the Special Issue Recent Advances in the Development and Application of Clay-Based Hybrid and Composite Materials)

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15 pages, 4837 KB

Open AccessArticle

First-Principles Investigation: Effects of Molybdenum Substitution on the Elastic Properties of Uranium Dioxide

by Haixin Xu, Jiaxuan Si, Hengheng Lv, Tao Peng, Peng Peng, Xin Wan, Tao Chen and Aitao Tang

Crystals 2026, 16(6), 378; https://doi.org/10.3390/cryst16060378 - 5 Jun 2026

Abstract

Uranium dioxide (UO₂) is the standard fuel in light water reactors, but improving its mechanical performance is essential for achieving higher burnups. This study employs first-principles density functional theory with the DFT + U approach to investigate the effect of molybdenum [...] Read more.

Uranium dioxide (UO₂) is the standard fuel in light water reactors, but improving its mechanical performance is essential for achieving higher burnups. This study employs first-principles density functional theory with the DFT + U approach to investigate the effect of molybdenum (Mo) substitution on the elastic properties of UO₂. Supercell models with Mo concentrations from 3.125 to 9.375 at.% are constructed, and elastic constants are calculated using the stress–strain method, complemented by Bader charge and charge density analyses. The results reveal a non-monotonic concentration-dependent behavior: at 3.125 at.% Mo, the shear and Young’s moduli increase by ~16% and ~14%, respectively, indicating significant stiffening; at higher concentrations (6.25 and 9.375 at.%), both moduli decrease, leading to softening of UO₂ lattice. Bader charge analysis shows that Mo loses only 0.13 electrons (vs. 2.56 for U) and the Mo–O bond is much shorter than the U–O bond; this is evidence of covalent bonding between Mo and O atoms that acts as local strengthening centers at low doping. The softening at higher concentrations is attributed to increased lattice distortion and enhanced bond delocalization, supported by changes in Cauchy pressure, Debye temperature, and Vickers hardness. The calculated elastic modulus and hardness of pure UO₂ are in good agreement with previously reported experimental data. For Mo-doped UO₂ systems, this work establishes a quantitative composition–property relationship, providing a theoretical reference for future experimental investigations. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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29 pages, 2156 KB

Open AccessArticle

Structural and Mechanical Properties of Y₂SiO₅-Lu₂SiO₅ Solid Solutions from Ab Initio Calculations

by Alexander Platonenko, Marina Konuhova, Dmitry V. Bocharov and Anatoli I. Popov

Crystals 2026, 16(6), 377; https://doi.org/10.3390/cryst16060377 - 4 Jun 2026

Abstract

Y₂SiO₅ (YSO) and Lu₂SiO₅ (LSO) are orthosilicates used in photonic and scintillation applications. Isovalent substitution on the rare-earth sublattice in YSO–LSO solid solutions enables systematic tuning of lattice parameters and elastic properties without changing the underlying monoclinic [...] Read more.

Y₂SiO₅ (YSO) and Lu₂SiO₅ (LSO) are orthosilicates used in photonic and scintillation applications. Isovalent substitution on the rare-earth sublattice in YSO–LSO solid solutions enables systematic tuning of lattice parameters and elastic properties without changing the underlying monoclinic structural framework. A systematic ab initio study of structural, elastic, and vibrational properties of Ce-free YSO–LSO solid solutions is performed within density functional theory using a localized Gaussian-type orbital basis. Nine compositions spanning the full range from YSO to LSO with a Lu content step of 12.5% are investigated. A total of 76 symmetry-independent Y/Lu substitution patterns are explicitly constructed. For each configuration, full geometry optimization and calculation of second-order elastic constants are carried out using the stress–strain approach. Bulk, shear, and Young’s moduli, as well as Poisson’s ratio, are obtained using the Voigt, Reuss, and Hill averaging schemes. Sound velocities and Debye temperatures are derived from the Hill-averaged elastic moduli and density. The unit-cell volumes decrease smoothly with increasing Lu content and follow Vegard’s law, indicating uniform lattice contraction. The Hill-averaged bulk modulus increases from 92 GPa (YSO) to 115 GPa (LSO), the Young’s modulus rises from 151 to 180 GPa, and a strong directional anisotropy (ratio ∼2) is preserved across the entire series. The Debye temperature decreases monotonically from 518 K to 439 K, indicating that the increase in mass density outweighs the stiffening-induced tendency toward higher sound velocities. These results provide quantitative guidance for composition selection and stress management in LYSO-based crystal detectors. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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19 pages, 4741 KB

Open AccessArticle

Multi-Phase Evolution and Surface Degradation Kinetics of a Non-Equiatomic (FeCoNiCr)₈₅Ga₁₅ High Entropy Alloy: The Role of Low-Temperature Thermal Activation

by Emmanuel Georgatis, Stavros Kiape, Margarita Ziavra, Anthoula Poulia and Alexander E. Karantzalis

Crystals 2026, 16(6), 376; https://doi.org/10.3390/cryst16060376 - 3 Jun 2026

Abstract

This study provides a rigorous analysis of the phase stability, mechanical behavior, and surface integrity of a non-equiatomic (FeCoNiCr)₈₅Ga₁₅ high-entropy alloy (HEA). By transitioning from the conventional equiatomic design to a gallium-doped 3d-transition metal matrix, we explore the interplay between [...] Read more.

This study provides a rigorous analysis of the phase stability, mechanical behavior, and surface integrity of a non-equiatomic (FeCoNiCr)₈₅Ga₁₅ high-entropy alloy (HEA). By transitioning from the conventional equiatomic design to a gallium-doped 3d-transition metal matrix, we explore the interplay between lattice distortion and phase separation. Synthesized via vacuum arc melting, the as-cast alloy exhibits a non-homogeneous dendritic morphology consisting of a Cr-Fe-Co rich face-centered cubic (FCC) matrix and Ni-Ga rich body-centered cubic (BCC) interdendritic regions. While global thermodynamic criteria (δ = 3.65, ΔH_mix = −9.28 kJ/mol, and Ω = 2.23) favor single-phase solid solution stability, the Valence Electron Concentration (VEC = 7.46) precisely forecasts this dual-phase structure. Following low-temperature annealing at 250 °C for 24 h, high lattice strain energy drives a significant morphological transformation where the continuous interdendritic network resolves into discrete, phase-separated B2/BCC “islands”. Mechanical and tribological characterizations reveal that this low-temperature thermal activation triggers precipitate hardening; the macro-hardness increases from 146 ± 11 HB to 153 ± 7.5 HB and the micro-hardness rises from 186 ± 4 HV_0.5 to 206 ± 17.5 HV_0.5, yielding enhanced resistance to oxidation-delamination wear. However, electrochemical evaluation in a 3.5 wt.% NaCl solution highlights a fundamental trade-off: the formation of localized galvanic micro-cells between the phase-separated islands and the matrix causes the corrosion current density (i_corr) to increase from ≈10⁻⁹ A/cm² in the as-cast state to ≈10⁻⁶ A/cm² post-heat treatment, accompanied by a heightened susceptibility to localized pitting. These findings elucidate the primary role of electronic structure and minor p-block additions in regulating the lifecycle performance of transition metal HEAs under extreme conditions. Full article

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

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17 pages, 8135 KB

Open AccessArticle

Viscosity of Low-Reactive Mold Flux and Its Correlation with Microstructure and Crystalline Phases

by Jie Qi, Jinhui Wang and Chengjun Liu

Crystals 2026, 16(6), 375; https://doi.org/10.3390/cryst16060375 - 3 Jun 2026

Abstract

For continuous casting of strong reducing steels, the low-reactive aluminate-based mold flux consisting of CaO-SiO₂-Al₂O₃-CaF₂-Li₂O-B₂O₃-Na₂O with low SiO₂ content was designed. The correlation between the melt [...] Read more.

For continuous casting of strong reducing steels, the low-reactive aluminate-based mold flux consisting of CaO-SiO₂-Al₂O₃-CaF₂-Li₂O-B₂O₃-Na₂O with low SiO₂ content was designed. The correlation between the melt structure under high temperature and the crystallization phases during the cooling process and the change of viscosity was analyzed. The following conclusions were obtained. The polymerization degree of the mold flux consistently decreased as the w(CaO)/w(Al₂O₃) ratio increased from 0.93 to 1.65. Due to melt structure depolymerization, the viscosity at 1300 °C dropped from 0.132 Pa·s to 0.054 Pa·s. As the w(CaO)/w(Al₂O₃) ratio increases near the breaking temperature, the crystalline phases in the mold flux transition from LiAlO₂ to Ca₂Al₂SiO₇, and finally to a combination of Ca₁₂Al₁₄O₃₂F₂ and LiAlO₂. The rapid viscosity increase at the breaking temperature was primarily due to the precipitation of these phases. Furthermore, influenced by the changes in crystallization tendency and crystalline phase precipitation, the breaking temperature first decreased and then increased. Increasing the Li₂O mass fraction from 5% to 9% led to a decrease in the polymerization degree of the mold flux. Due to the depolymerizing impact of Li₂O on the slag network, the mold flux viscosity at 1300 °C decreased from 0.102 Pa·s to 0.047 Pa·s. The breaking temperature of the mold flux rose notably with a higher Li₂O mass fraction. At the breaking temperature, the crystalline phases in the mold flux transition from Ca₂Al₂SiO₇ to a combination of LiAlO₂ and Ca₁₂Al₁₄O₃₂F₂. The precipitation of these phases at the breaking temperature directly caused a rapid increase in viscosity. The results systematically reveal the coupling mechanism between melt structure, crystalline phase evolution, and viscosity variation of low-SiO₂ aluminate-based mold flux, which provides an important theoretical basis for composition design and performance regulation of mold fluxes for high-aluminum steel continuous casting. Full article

(This article belongs to the Special Issue Metallurgy-Processing-Properties Relationship of Metallic Materials)

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20 pages, 2708 KB

Open AccessArticle

Compositional Characterization and Color Genesis of Precious Coral Based on Multi-Spectroscopic Techniques

by Yushu Yang, Ying Guo, Zhe Hu and Jiayang Han

Crystals 2026, 16(6), 374; https://doi.org/10.3390/cryst16060374 - 2 Jun 2026

Abstract

The color origin of precious coral, a highly valued biogenic polycrystalline gemstone, has long remained elusive. In this study, an integrated approach employing spectrophotometry, Raman, FTIR, and UV-Vis spectroscopy, coupled with Spearman correlation analysis, was utilized to investigate a color-graded series of precious [...] Read more.

The color origin of precious coral, a highly valued biogenic polycrystalline gemstone, has long remained elusive. In this study, an integrated approach employing spectrophotometry, Raman, FTIR, and UV-Vis spectroscopy, coupled with Spearman correlation analysis, was utilized to investigate a color-graded series of precious coral samples ranging from white to red. The results demonstrate that the calcareous composition of the samples tested in our study consists exclusively of calcite. The actual chromophores are identified as a blend of multiple distinct polyene species, characterized by Raman shifts at 1126 and 1515 cm⁻¹, with density functional theory (DFT) calculations determining the number of conjugated (C=C) bonds in the polyene chain to be 10–11. Inherently exhibiting a red-orange hue, the progressive accumulation of these polyenes drives a systematic color transition from orange to red. Both absorption bands at 314 nm and 532 nm in the UV-Vis spectra are attributed to the polyene pigment molecules. Specifically, the broad 532 nm band is dominated by π-π* electronic transitions, while the 314 nm band likely arises from terminal benzene rings and their derivatives. As the pigment concentration increases, this band exhibits pronounced broadening and an increase in absorbance, accompanied by a redshift in the maximum absorption peak. This spectral evolution leads to an intensified absorption in the yellow-orange region, elucidating the intrinsic mechanism underlying the color transition of precious coral from orange to red with increasing pigment content. This work lays a solid foundation for the non-destructive identification of precious corals and future research on their color genesis. Full article

(This article belongs to the Special Issue Modern Gem Crystals: Synthesis, Characterization, Genesis and Intelligent Analysis)

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14 pages, 17168 KB

Open AccessArticle

Collaborative Surface Modification of Alloy Wire and Wheel for Enhanced Photothermal Performance in a Solar-Driven NiTi Rotary Engine

by Xiangshen Kong, Yixin Chen, Xinyang Wang, Shuaidong Qi and Haibin Zhang

Crystals 2026, 16(6), 373; https://doi.org/10.3390/cryst16060373 - 2 Jun 2026

Abstract

Solar-driven NiTi alloy wire rotary engines are promising for lightweight actuation, but their performance is often restricted by insufficient light absorption of the alloy wire and unstable wheel–wire transmission. In this work, a collaborative surface-modification strategy was developed by combining a CNT/PDA-based photothermal [...] Read more.

Solar-driven NiTi alloy wire rotary engines are promising for lightweight actuation, but their performance is often restricted by insufficient light absorption of the alloy wire and unstable wheel–wire transmission. In this work, a collaborative surface-modification strategy was developed by combining a CNT/PDA-based photothermal coating on the NiTi alloy wire with a CNT/PDMS-based coating on the wheel surface. To establish a controllable wire-coating process, electrophoretic deposition parameters were first screened on titanium plates using an orthogonal design involving voltage, duty ratio, water content, treatment time, and electrode distance. Among the tested conditions, an electrode distance of 10 mm provided the most favorable balance between coating thickness and microstructural uniformity, while water content and electrode distance were identified as the main factors affecting coating variation. After transfer to the alloy wire, the coating greatly reduced reflectance in the 300–1400 nm range and significantly enhanced photothermal heating, increasing the maximum irradiation temperature by about 30 °C. On the wheel side, PDMS-based surface modification further improved rotational output, and the 1.5 wt% + 10 wt% formulation showed the best performance. In coupled rotation tests, the system with simultaneous wire and wheel modification exhibited the fastest startup and the highest angular velocity, reaching about five times that of the slowest rotating modified group. These results demonstrate that coordinated surface modification of the alloy wire and wheel is an effective route to improving the photothermal response and rotational performance of NiTi alloy wire rotary engines. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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20 pages, 9479 KB

Open AccessArticle

Mechanical Properties and Microstructure of Alkali-Activated Fiber-Reinforced Mortar Incorporating Red Mud and Fly Ash

by Xiangqin Du, Tingjie Wu, Zhilong Liu, Guang Xu, Yuanshuai Zhu, Chunyi Wang and Xingjie Liu

Crystals 2026, 16(6), 372; https://doi.org/10.3390/cryst16060372 - 2 Jun 2026

Abstract

Red mud (RM) and fly ash (FA) were used as a 30% replacement of cement in a sodium silicate-activated system. Composite mortar specimens with RM/FA ratios of 0:30, 1:5, 1:2, 1:1, and 2:1 were prepared with polypropylene fibers (PPF) for toughness enhancement. The [...] Read more.

Red mud (RM) and fly ash (FA) were used as a 30% replacement of cement in a sodium silicate-activated system. Composite mortar specimens with RM/FA ratios of 0:30, 1:5, 1:2, 1:1, and 2:1 were prepared with polypropylene fibers (PPF) for toughness enhancement. The mechanical properties and microstructure of the fiber-reinforced mortar were systematically investigated. The results showed that RM20F10 (RM/FA = 2:1) exhibited the best overall mechanical performance among all tested proportions. At this ratio, the 28-day compressive, flexural, and splitting tensile strengths reached 32.4 MPa, 7.3 MPa, and 4.2 MPa, exceeding the control mortar by 12.5%, 15.9%, and 23.5%, respectively. The RM/FA ratio of 1:1 achieved the highest 7-day flexural-to-compressive strength ratio. At 28 days, autogenous shrinkage increased from 910 με to 1100 με as the RM/FA ratio rose from 0:30 to 2:1, and all RM-containing specimens exhibited higher water absorption than the control mortar. Microstructural analysis by SEM, XRD, and FTIR revealed a denser matrix with reduced porosity, attributed to the synergistic formation of C–S–H, C–A–S–H, and N–A–S–H gels. RM reduced early-age porosity by promoting C–A–S–H gel formation, while FA facilitated late-age densification through delayed activation. PPF effectively bridged microcracks via fiber pull-out, leading to a ductile failure mode. Full article

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

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14 pages, 6495 KB

Open AccessArticle

Development of a Non-Invasive Biosensor Utilizing an Erbium Phthalocyanine Colloid for Potential Glucose Detection in Saliva

by Diego Hernán Cuate Gómez, Jesús Manuel Lugo Quintal, Carlos Zuñiga Islas, Abel Garzón Roman and José Luis Sosa Sánchez

Crystals 2026, 16(6), 371; https://doi.org/10.3390/cryst16060371 - 2 Jun 2026

Abstract

This study presents a novel biosensor for non-invasive glucose detection in saliva using sol colloids of erbium phthalocyanine (ErPc) and polyvinyl acetate (PVAc). The sensors were manufactured by depositing thin films on glass substrates and characterized via optical transmission spectroscopy in the UV-Vis [...] Read more.

This study presents a novel biosensor for non-invasive glucose detection in saliva using sol colloids of erbium phthalocyanine (ErPc) and polyvinyl acetate (PVAc). The sensors were manufactured by depositing thin films on glass substrates and characterized via optical transmission spectroscopy in the UV-Vis range. The detection signal was based on variations in the transmission spectra amplitude after glucose intake. Results showed that the transmission response effectively distinguished between three health conditions: a regular individual, an athlete, and a prediabetic patient. Specifically, the relative transmission increased significantly in the prediabetic subject compared to the healthy individuals, demonstrating the biosensor’s capability to track glucose fluctuations non-invasively. Full article

(This article belongs to the Special Issue Design and Development of Silicon Heterostructures for Electronics and Photonics)

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21 pages, 4174 KB

Open AccessArticle

Superconfined Antiferromagnons on the Two-Dimensional Penrose Lattice

by Takashi Inoue and Shoji Yamamoto

Crystals 2026, 16(6), 370; https://doi.org/10.3390/cryst16060370 - 1 Jun 2026

Abstract

We find novel confined states in the spin-S nearest-neighbor antiferromagnetic Heisenberg model on the two-dimensional Penrose lattice. Linear spin waves have massively degenerate eigenstates strictly confined to tricoordinated sites. They contrast with the well-known itinerant analogs in the tight-binding model, where electrons [...] Read more.

We find novel confined states in the spin-S nearest-neighbor antiferromagnetic Heisenberg model on the two-dimensional Penrose lattice. Linear spin waves have massively degenerate eigenstates strictly confined to tricoordinated sites. They contrast with the well-known itinerant analogs in the tight-binding model, where electrons are confined but extended to both tricoordinated and pentacoordinated sites. It is the site potentials in the spin-wave Hamiltonian, originating from Coulomb interactions between electrons, that confine spin waves to minimally coordinated sites only. Confined states in the tight-binding Hamiltonian consist of six types of building blocks, whereas those in the spin-wave Hamiltonian consist of only four of them. Confined spin waves are robust against 1/S corrections. Emergent O(S⁰) interactions further confine—superconfine—spin waves into two separate groups within tricoordinated sites. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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