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Single Crystal Growth and Structural Study of the New MCu₂Zn₂₀ (M = Nb, Hf) Compounds
Synthesis, Crystal Structure, DFT Analysis and Docking Studies of a Novel Spiro Compound Effecting on EGR-1-Regulated Gene Expression
The Effect of High-Temperature Annealing on the Magnetic and Structural Properties of (MnFePSi)-Based Glass-Coated Microwires

Journal Description

Crystals

Crystals is an international, peer-reviewed, open access journal on Crystallography published monthly online by MDPI. The Professional Committee of Key Materials and Technology for Electronic Components (PC-KMTEC) is affiliated with Crystals and its members receive discounts on the article processing charges.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, Ei Compendex, CAPlus / SciFinder, and other databases.
Journal Rank: JCR - Q2 (Crystallography) / CiteScore - Q2 (Condensed Matter Physics)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 12.7 days after submission; acceptance to publication is undertaken in 2.6 days (median values for papers published in this journal in the first half of 2025).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.

Impact Factor: 2.4 (2024); 5-Year Impact Factor: 2.4 (2024)

Imprint Information Journal Flyer Open Access ISSN: 2073-4352

Latest Articles

10 pages, 1150 KiB

Open AccessArticle

Crystal Structure of 4′-Phenyl-1′,4′-Dihydro-2,2′:6′,2″-Terpyridine: An Intermediate from the Synthesis of Phenylterpyridine

by Alexander Sedykh, Maksim Zhernakov, Mariia Becker, Dirk G. Kurth and Klaus Müller-Buschbaum

Crystals 2025, 15(7), 619; https://doi.org/10.3390/cryst15070619 - 1 Jul 2025

The intermediate compound 4′-phenyl-1′,4′-dihydro-2,2′:6′,2″-terpyridine (pdhtpy) was isolated for the first time during the synthesis of 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy) and characterised by single-crystal X-ray diffraction. Pdhtpy crystallises in the triclinic crystal system with space group P‾1 with the following unit cell [...] Read more.

The intermediate compound 4′-phenyl-1′,4′-dihydro-2,2′:6′,2″-terpyridine (pdhtpy) was isolated for the first time during the synthesis of 4′-phenyl-2,2′:6′,2″-terpyridine (ptpy) and characterised by single-crystal X-ray diffraction. Pdhtpy crystallises in the triclinic crystal system with space group P‾1 with the following unit cell parameters at 100 K: a = 6.1325(4) Å; b = 8.2667(5) Å; c = 16.052(2) Å; α = 86.829(2)°; β = 82.507(2)°; γ = 84.603(2)°; V = 802.49(9) Å³. The absence of stabilising electron-withdrawing groups renders pdhtpy prone to oxidative conditions. Pdhtpy was obtained as a mixture with ptpy, confirmed by Rietveld refinement of the powder X-ray diffraction pattern. Notably, pdhtpy is the first solid-state 1,4-dihydropyridine lacking electron-withdrawing groups at both positions 3 and 5, distinguishing it from Hantzsch esters and related compounds. Full article

(This article belongs to the Section Organic Crystalline Materials)

28 pages, 5647 KiB

Open AccessReview

Effect of Interstitial Oxygen on the Microstructure and Mechanical Properties of Titanium Alloys: A Review

by Yaojia Ren, Jiajun Xu, Yingkang Wei, Yingying Liu, Jilei Zhu and Shifeng Liu

Crystals 2025, 15(7), 618; https://doi.org/10.3390/cryst15070618 - 30 Jun 2025

Titanium alloys are of significant value in aerospace, biomedical, and marine engineering applications due to their excellent specific strength and favorable biocompatibility. As a crucial interstitial solute, oxygen significantly influences the mechanical properties of titanium alloys. However, excessive oxygen content can lead to [...] Read more.

Titanium alloys are of significant value in aerospace, biomedical, and marine engineering applications due to their excellent specific strength and favorable biocompatibility. As a crucial interstitial solute, oxygen significantly influences the mechanical properties of titanium alloys. However, excessive oxygen content can lead to severe embrittlement and a significant reduction in ductility. This paper systematically reviews the mechanisms of microstructural evolution induced by oxygen in conventionally manufactured titanium alloys and their impact on mechanical properties, highlighting that conventional processes require complex post-treatments (PT) to achieve a balance between strength and plasticity. This assessment further explores the regulatory mechanisms of oxygen on the microstructure and mechanical properties of laser additive manufactured (LAM) titanium alloys, elucidating the fundamental phenomena regarding the oxygen–microstructure–property relationship. Finally, based on the current research progress, this paper provides an outlook on the future development directions and key research priorities in this field. This review offers valuable insights into the role of oxygen in titanium alloys and the development of high-performance titanium alloys. Full article

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

15 pages, 1542 KiB

Open AccessArticle

Investigation on Tensile Behavior of Solid Solution-Strengthened Ni-Co-Cr-Based Superalloy During Long-Term Aging

by Wanqi Hou, Xianjun Guan, Jiaqi Wang, Jinrong Wu, Lanzhang Zhou and Zheng Jia

Crystals 2025, 15(7), 617; https://doi.org/10.3390/cryst15070617 - 30 Jun 2025

This study investigated how long-term aging (750 °C and 950 °C) affects the microstructure and room-temperature tensile properties of the Ni-Co-Cr superalloy GH3617. Characterization (SEM, EDS, EBSD) showed that initial aging (750 °C, 500 h) formed discontinuous M₂₃C₆ carbides, pinning [...] Read more.

This study investigated how long-term aging (750 °C and 950 °C) affects the microstructure and room-temperature tensile properties of the Ni-Co-Cr superalloy GH3617. Characterization (SEM, EDS, EBSD) showed that initial aging (750 °C, 500 h) formed discontinuous M₂₃C₆ carbides, pinning grain boundaries and improving strength. Prolonged aging (750 °C, 5000 h) caused M₂₃C₆ to coarsen into brittle chain-like structures (width up to 1.244 μm) and precipitated M₆C carbides, degrading grain boundaries. Aging at 950 °C accelerated this coarsening via LSW kinetics (rate constant: 6.83×10⁻² μm³/s), with Mo segregation promoting M₆C formation. Tensile properties resulted from competing γ′ precipitation strengthening (post-aging strength increased up to 23.3%) and grain boundary degradation (elongation dropped from 70.1% to 43.3%). Fracture shifted from purely intergranular (cracks along M₂₃C₆/γ interfaces at 750 °C) to mixed mode (cracks initiated by M₆C fragmentation at 950 °C). These insights support superalloy microstructure optimization and lifetime prediction. Full article

(This article belongs to the Special Issue Crystal Plasticity (4th Edition))

12 pages, 19225 KiB

Open AccessArticle

Microstructure, Mechanical Properties, Deformation Behavior, and Crystallographic Texture of the Al-Gd-Cr-Ti Quaternary Alloy for Thermal Neutron Absorption

by Sayed M. Amer, Dmitry I. Nikolayev, Tatiana A. Lychagina, Abdelmoneim El-Khouly, Ruslan Yu. Barkov, Alexey S. Prosviryakov, Anastasia V. Mikhaylovskaya, Maria V. Glavatskikh and Andrey V. Pozdniakov

Crystals 2025, 15(7), 616; https://doi.org/10.3390/cryst15070616 - 30 Jun 2025

In this work, we report the identification of a novel quaternary intermetallic phase (Al₂₁GdCrTi) formed during the solidification of a novel Al–Gd–Cr–Ti alloy, which has not been previously documented in the literature to the best of our knowledge. The study also [...] Read more.

In this work, we report the identification of a novel quaternary intermetallic phase (Al₂₁GdCrTi) formed during the solidification of a novel Al–Gd–Cr–Ti alloy, which has not been previously documented in the literature to the best of our knowledge. The study also provides a detailed analysis of microstructure evolution, texture behavior, and the mechanical strengthening effect of rolling processes, along with neutron absorption performance. XRD analysis reveals that the intensity of (022), (113) planes of the as-hot-cold-rolled sample is higher than that of the as-cast due to the change in the direction of some grains in these planes during rolling. The results indicate that the studied alloys scatter neutrons about 100 times less than a nearly pure aluminum alloy. The hardness of the as-cast alloy increased from 36 to 53 HV after cold rolling and to 50 HV after hot rolling-cold rolling. Hot-cold-rolled alloy has a yield strength of 160 MPa and an ultimate tensile strength of 181 MPa, while maintaining an elongation of 11.3%. The studied alloys, containing 4.2 wt.% of the alloying elements 3.8Gd, 0.2Cr, and 0.2Ti (Al-3.8Gd-0.2Cr-0.2Ti), exhibited a yield strength 28 MPa higher than those containing 21 wt.% of the alloying elements 5Cu, 6Gd, and 8Bi (Al-5Cu-6Gd-8Bi). The studied alloys form the basis for the development of high-technology Al-Gd alloys for neutron shielding. Full article

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

21 pages, 5673 KiB

Open AccessArticle

Functionalized Magnetic Nanomaterial Based on SiO₂/Ca(OH)₂-Coated Clusters Decorated with Silver Nanoparticles for Dental Applications

by Izabell Crăciunescu, George Marian Ispas, Alexandra Ciorîta and Rodica Paula Turcu

Crystals 2025, 15(7), 615; https://doi.org/10.3390/cryst15070615 - 30 Jun 2025

In this study, an innovative dental functionalized magnetic nanomaterial was developed by incorporating hydrophilic magnetic clusters as an alternative to conventional isolated magnetic nanoparticles, introducing a novel structural and functional concept in dental applications. The ~100 nm magnetic clusters—composed of densely packed 7 [...] Read more.

In this study, an innovative dental functionalized magnetic nanomaterial was developed by incorporating hydrophilic magnetic clusters as an alternative to conventional isolated magnetic nanoparticles, introducing a novel structural and functional concept in dental applications. The ~100 nm magnetic clusters—composed of densely packed 7 nm Fe₃O₄ nanoparticles—were sequentially coated with a silica (SiO₂) layer (3–5 nm) to improve chemical and mechanical stability, followed by an outer calcium hydroxide [Ca(OH)₂] layer to enhance bioactivity and optical integration. This bilayer architecture enables magnetic field-assisted positioning and improved dispersion within dental resin matrices. Silver nanoparticles were incorporated to enhance antimicrobial activity and reduce biofilm formation. The synthesis process was environmentally friendly and scalable. Comprehensive physicochemical characterization confirmed the material’s functional performance. Saturation magnetization decreased progressively with surface functionalization, from 62 to 14 emu/g, while the zeta potential became increasingly negative (from −2.42 to −22.5 mV), supporting its ability to promote apatite nucleation. The thermal conductivity (0.527 W/m·K) closely matched that of human dentin (0.44 W/m·K), and the colorimetric analysis showed improved brightness (ΔL = 5.3) and good color compatibility (ΔE = 11.76). These results indicate that the functionalized magnetic nanomaterial meets essential criteria for restorative use and holds strong potential for future clinical applications. Full article

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

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14 pages, 1768 KiB

Open AccessArticle

Properties of Cast Iron Produced with a Limited Share of Pig Iron in the Charge

by Krzysztof Janerka and Jan Jezierski

Crystals 2025, 15(7), 614; https://doi.org/10.3390/cryst15070614 - 30 Jun 2025

The article presents issues related to the melting of cast iron with a limited or zero share of pig iron in the charge. The results of melts conducted in electric induction furnaces are presented. The elimination of pig iron and its replacement with [...] Read more.

The article presents issues related to the melting of cast iron with a limited or zero share of pig iron in the charge. The results of melts conducted in electric induction furnaces are presented. The elimination of pig iron and its replacement with steel or return scrap is highly significant in the context of sustainable production and product life cycle assessment (LCA). The paper presents the results of research carried out during melts conducted under both laboratory and industrial conditions. The chemical composition of the cast iron, its physicochemical properties obtained from the analysis of the cooling curve and its derivative, as well as the structure, were analyzed. It was found that cast iron produced using high-quality steel scrap contains fewer sulfur and phosphorus impurities. However, it was also observed that such cast iron exhibits reduced nucleation ability, which can be improved by applying an inoculation process. Full article

18 pages, 3863 KiB

Open AccessArticle

The Temperature Sensitivity of the Piezoelectric Thickness Shear Mode of α-GeO₂ Single Crystals

by Philippe Papet and Pascale Armand

Crystals 2025, 15(7), 613; https://doi.org/10.3390/cryst15070613 - 30 Jun 2025

This paper focuses on identifying temperature-compensated Y-cuts (using a Cartesian coordinate system) in a piezoelectric α-GeO₂ single crystal, which is isostructural–quartz α-SiO₂. The study aims to minimize the frequency drift of the thickness shear mode by analyzing the resonant frequency’s [...] Read more.

This paper focuses on identifying temperature-compensated Y-cuts (using a Cartesian coordinate system) in a piezoelectric α-GeO₂ single crystal, which is isostructural–quartz α-SiO₂. The study aims to minimize the frequency drift of the thickness shear mode by analyzing the resonant frequency’s first- and second-order temperature coefficients T_f⁽¹⁾ and T_f⁽²⁾. To obtain these, the first-order, T_Cij⁽¹⁾, and second-order, T_Cij⁽²⁾, temperature coefficients of the elastic constant, C_ij, previously obtained from room temperature up to 900 °C, were calculated. Upon heating, the thermal behavior of the elastic constants indicated that some, such as C₁₁ and C₃₃, are stable over a range of temperatures, while others, such as C₄₄ and C₆₆, increase with the temperature. This paper also explores a family of singly and doubly rotated Y-cuts of α-GeO₂, revealing cuts with a potential application for temperature compensation and/or linear dependence over the temperature range. The results are compared with those of the well-known piezoelectric isomorph material α-SiO₂. The findings highlight that α-GeO₂ is a promising material for piezoelectric devices in high-temperature environments, outperforming α-SiO₂ (α-quartz), which is limited by a solid–solid phase transition at 573 °C. Full article

(This article belongs to the Section Crystal Engineering)

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15 pages, 2316 KiB

Open AccessArticle

Enhancement of Ethylene-Butene Terpolymer Performance via Carbon Nanotube-Induced Nanodispersion of Montmorillonite Layers

by Li Zhang, Jianming Liu, Duanjiao Li, Wenxing Sun, Zhi Li, Yongchao Liang, Qiang Fu, Nian Tang, Bo Zhang, Fei Huang, Xuelian Fan, Yuansi Wei, Pengxiang Bai and Yuqi Wang

Crystals 2025, 15(7), 612; https://doi.org/10.3390/cryst15070612 - 30 Jun 2025

In this study, the enhancement mechanism of the nano-dispersion of stearic acid-modified montmorillonite (SMMT) induced by carbon nanotubes (CNTs) in ethylene-butene terpolymer (EBT) was comprehensively investigated, and the regulation effect of composite fillers on EBT properties was revealed. Scanning electron microscopy (SEM) confirmed [...] Read more.

In this study, the enhancement mechanism of the nano-dispersion of stearic acid-modified montmorillonite (SMMT) induced by carbon nanotubes (CNTs) in ethylene-butene terpolymer (EBT) was comprehensively investigated, and the regulation effect of composite fillers on EBT properties was revealed. Scanning electron microscopy (SEM) confirmed that SMMT achieved homogeneous nanoscale dispersion after CNT addition, and the size of aggregates was greatly reduced. Four-cycle strain-scanning analysis revealed a 200% increase in rubber–filler (R-F) interaction strength due to CNT incorporation. At the optimal CNT/SMMT ratio of 1:5, the EBT composites exhibited a 40.4% increase in Young’s modulus, 71.4% enhancement in tensile strength, and maintained 250% elongation at break, effectively addressing the strength–toughness trade-off of traditional rigid fillers. Thermogravimetric analysis (TGA) showed near 20 °C elevation in EBT composites’ maximum decomposition temperature, while water contact angle measurements indicated a hydrophobicity increase to 117.5° and water absorption rate below 0.2%. The quantitative improvement in thermal oxidation stability and hydrophobic barrier performance was achieved simultaneously. Full article

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17 pages, 4438 KiB

Open AccessArticle

Y₅F₃[AsO₃]₄ and Y₅Cl₃[AsO₃]₄: Two Non-Isostructural Yttrium Halide Oxoarsenates(III) and Their Potential as Hosts for Luminescent Eu³⁺- and Tb³⁺-Doping

by Ralf J. C. Locke, Martina Mikuta, Florian Ledderboge, Frank C. Zimmer, Henning A. Höppe and Thomas Schleid

Crystals 2025, 15(7), 611; https://doi.org/10.3390/cryst15070611 - 30 Jun 2025

Y₅F₃[AsO₃]₄ crystallizes needle-shaped in the tetragonal space group P4/ncc with the lattice parameters a = 1143.80(8) pm, c = 1078.41(7) pm and c/a = 0.9428 for Z = 4. The yttrium-fluoride substructure [...] Read more.

Y₅F₃[AsO₃]₄ crystallizes needle-shaped in the tetragonal space group P4/ncc with the lattice parameters a = 1143.80(8) pm, c = 1078.41(7) pm and c/a = 0.9428 for Z = 4. The yttrium-fluoride substructure linked via secondary contacts forms a three-dimensional network

\begin{matrix} 3 \\ \infty \end{matrix}

{[Y₅F₃]¹²⁺} and the remaining part consists of ψ¹-tetrahedral [AsO₃]³⁻ units, which leave lone-pair channels along [001]. In contrast, platelet-shaped Y₅Cl₃[AsO₃]₄ crystals adopt the monoclinic space group C2/c with the lattice parameters a = 1860.56(9) pm, b = 536.27(3) pm, c = 1639.04(8) pm and β = 105.739(3)° for Z = 4. Condensation of [(Y1,2)O₈]¹³⁻ polyhedra via four common edges each leads to fluorite-like

\begin{matrix} 2 \\ \infty \end{matrix}

{[(Y1,2)O

\begin{matrix} e \\ 8 / 2 \end{matrix}

]⁵⁻} layers spreading out parallel to the (100) plane. Their three-dimensional linkage occurs via the (Y3)³⁺ cations with their Cl⁻ ligands on the one hand and the As³⁺ cations with their lone-pairs of electrons on the other, which also form within [AsO₃]³⁻ anions lone-pair channels along [010]. Both colorless compounds can be obtained by solid-state reactions from corresponding mixtures of the binaries (Y₂O₃, As₂O₃ and YX₃ with X = F and Cl) at elevated temperatures of 825 °C, most advantageously under halide-flux assistance (CsBr for Y₅F₃[AsO₃]₄ and ZnCl₂ for Y₅Cl₃[AsO₃]₄). By replacing a few percent of YX₃ with EuX₃ or TbX₃, Eu³⁺- or Tb³⁺-doped samples are accessible, which show red or green luminescence upon excitation with ultraviolet radiation. Full article

(This article belongs to the Special Issue Synthesis and Crystal Structure of Rare-Earth Metal Compounds)

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18 pages, 9619 KiB

Open AccessArticle

Fractional Vortex Dynamics in Two-Band Superconductors with Linear Normal Strips

by Ariday S. Mosquera-Polo, Edwan A. Aríza-Echeverri, Cristhian Aguirre, Luis F. Muñoz-Martínez and Julián Faúndez

Crystals 2025, 15(7), 610; https://doi.org/10.3390/cryst15070610 - 30 Jun 2025

We investigate the impact of normal linear strips—both perpendicular and parallel to the direction of vortex motion—on the dynamics of fractional vortices in a two-band superconducting slab. In the absence of pinning, composite vortices dominate throughout the sample, while non-composite (dissociated) vortices appear [...] Read more.

We investigate the impact of normal linear strips—both perpendicular and parallel to the direction of vortex motion—on the dynamics of fractional vortices in a two-band superconducting slab. In the absence of pinning, composite vortices dominate throughout the sample, while non-composite (dissociated) vortices appear only near the vortex entry edge, with energy dissipation primarily governed by the motion of composite structures. To modulate vortex behavior, we introduce linear regions of locally suppressed superconductivity, oriented either perpendicular or parallel to the vortex trajectory. A single perpendicular strip confines fractional vortices to the injection region, whereas two perpendicular strips stabilize composite vortices in the central domain and induce fractional vortex states near the boundaries. In contrast, parallel strips promote the dissociation of vortices across the entire sample, significantly altering the spatial configuration and dynamics of the vortex matter. Furthermore, the interband correlation coefficient serves as a direct indicator of the degree of spatial overlap between vortices in the two condensates. These findings highlight the critical role of pinning geometry in shaping vortex dynamics and energy dissipation, offering new strategies for controlling flux behavior in multiband superconductors for technological applications. Full article

(This article belongs to the Special Issue Superconductivity and Condensed Matter Physics)

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16 pages, 8434 KiB

Open AccessArticle

Micro-Alloying with Samarium to Enhance the Thermal Conductivity and Mechanical Properties of Al-5Ni Cast Alloys

by Yi Huang, Kang Wang, Zhisheng Zhu, Wenxue Cheng and Wenfang Li

Crystals 2025, 15(7), 609; https://doi.org/10.3390/cryst15070609 - 30 Jun 2025

The research focuses on how the samarium (Sm) addition amount affects the microstructural development, mechanical characteristics, and thermal conductivity of Al-5wt%Ni alloys. Microstructural characterization revealed that minor Sm additions concurrently refined α-Al grains and eutectic structures (α-Al + Al₃Ni), attributed to [...] Read more.

The research focuses on how the samarium (Sm) addition amount affects the microstructural development, mechanical characteristics, and thermal conductivity of Al-5wt%Ni alloys. Microstructural characterization revealed that minor Sm additions concurrently refined α-Al grains and eutectic structures (α-Al + Al₃Ni), attributed to the reduced initial nucleation temperature of α-Al and an adsorption inhibition effect on Al₃Ni phase formation. The experimental findings revealed that the integration of Sm improved the yield strength, maximum tensile strength, and heat conduction. The enhancements were chiefly driven by three processes: the refinement of grains, the improvement of the eutectic structure’s morphology, and diminishing the dissolvability of Fe/Si impurities within the α-Al matrix. The combined improvement of mechanical and thermal characteristics via regulated Sm addition offers a hopeful approach for the microstructural design of Al-Ni alloys. This study provides a crucial basis for the production of Al-Ni alloys that possess high thermal conductivity and satisfactory mechanical properties. Full article

(This article belongs to the Special Issue Design, Development and Processing of Aluminium Alloys and Their Composite Materials)

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18 pages, 1871 KiB

Open AccessArticle

Magnesia Partially Stabilized Zirconia/Hydroxyapatite Biocomposites: Structural, Morphological and Microhardness Properties

by Liliana Bizo, Adriana-Liana Bot, Marieta Mureșan-Pop, Lucian Barbu-Tudoran, Claudia Andreea Cojan and Réka Barabás

Crystals 2025, 15(7), 608; https://doi.org/10.3390/cryst15070608 - 30 Jun 2025

Hydroxyapatite (HAP) is the most widely accepted biomaterial for repairing bone tissue defects, demonstrating excellent biocompatibility and bioactivity that promote new bone formation. Zirconia (ZrO₂), known for its strength and fracture toughness, is commonly used to reinforce ceramics. In this study, [...] Read more.

Hydroxyapatite (HAP) is the most widely accepted biomaterial for repairing bone tissue defects, demonstrating excellent biocompatibility and bioactivity that promote new bone formation. Zirconia (ZrO₂), known for its strength and fracture toughness, is commonly used to reinforce ceramics. In this study, magnesium oxide (MgO) served as a stabilizer for zirconia, resulting in magnesia partially stabilized zirconia (Mg-PSZ). Both Mg-PSZ and HAP were synthesized via coprecipitation and mixed in specific ratios to create composites through a ceramic method involving mixing, compaction, and sintering at 1100 °C. The samples were characterized using techniques such as X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS). Structural analyses confirmed the presence of both monoclinic and tetragonal zirconia phases. Besides, the increased wt.% HAP in the composites produced distinct peaks for hexagonal HAP. Crystallite sizes ranged from 27.45 nm to 31.5 nm, and surface morphology was homogeneous with small pores. Elements such as calcium, phosphorus, magnesium, zirconium, and oxygen were detected in all samples. This research also examined microhardness changes in the materials. The findings revealed enhancement in microhardness for the biocomposite with higher zirconia content, 90Mg-PSZ/10HAP sample, with the smallest average pore size, highlighting its potential for biomedical applications. Full article

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

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14 pages, 3538 KiB

Open AccessArticle

Diamond-like Cage Motifs in {Cu₆(S^tBu)₄} Complexes with Pyridines

by Taisiya S. Sukhikh, Maxim N. Sokolov and Pavel A. Abramov

Crystals 2025, 15(7), 607; https://doi.org/10.3390/cryst15070607 - 28 Jun 2025

The reduction of Cu(NO₃)₂ by HS^tBu in CH₃CN under Ar atmosphere produces a light-yellow solution containing numerous {Cu_x(S^tBu)_y} species. The addition of different pyridines (py-R) into this solution results in [...] Read more.

The reduction of Cu(NO₃)₂ by HS^tBu in CH₃CN under Ar atmosphere produces a light-yellow solution containing numerous {Cu_x(S^tBu)_y} species. The addition of different pyridines (py-R) into this solution results in the formation of {Cu₆(S^tBu)₄} hexanuclear complexes. The slow Et₂O diffusion leads to crystals of [Cu₆(S^tBu)₄(2-Me-py)₅(CH₃CN)(NO₃)](NO₃) (1), [Cu₆(S^tBu)₄(Me₃py)₄(NO₃)₂]·3.5CH₃CN (2a), [Cu₆(S^tBu)₄(Me₃py)₅(NO₃)](NO₃)·5CH₃CN (2b), (NHEt₃)[Cu₆(S^tBu)₄(CH₃CN)₃(NO₃)₃]·H₂O (3), [Cu₆(S^tBu)₄(2-Br-py)₄(NO₃)₂]·2-Br-Py (4), [Cu₆(S^tBu)₄(3-Br-py)₆][Cu₆(S^tBu)₄(CH₃CN)₆](NO₃)₄·9CH₃CN (5), and [Cu₆(S^tBu)₄(3-Cl-py)₆][Cu₆(S^tBu)₄(CH₃CN)₆](NO₃)₄·5CH₃CN (6). The titled compounds were characterized by single crystal X-ray diffraction (SCXRD). The Cu···Cu contacts were analyzed with quantum chemical methods. Full article

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17 pages, 4381 KiB

Open AccessArticle

The Influence of Different Foaming Agents on the Properties and Foaming Mechanisms of Foam Ceramics from Quartz Tailings

by Huiyang Gao and Jie Zhang

Crystals 2025, 15(7), 606; https://doi.org/10.3390/cryst15070606 - 28 Jun 2025

The type of foaming agent significantly influences the pore structure and properties of foam ceramics, particularly their compressive strength. This study used quartz sand tailings and waste glass powder as raw materials to fabricate foam ceramic materials. The effects of different foaming agents [...] Read more.

The type of foaming agent significantly influences the pore structure and properties of foam ceramics, particularly their compressive strength. This study used quartz sand tailings and waste glass powder as raw materials to fabricate foam ceramic materials. The effects of different foaming agents (SiC, CaCO₃, and MnO₂) on the phase evolution, microstructure, pore size distribution, and physical properties of the foam ceramics were investigated, and the foaming mechanisms were elucidated. The results indicated that when SiC was employed as the foaming agent, the viscosity was high at elevated temperatures and pores with irregular shapes tended to form because of the anisotropy of the quartz crystals. CaO generated from CaCO₃ decomposition reduced the melt viscosity by disrupting the [SiO₄] tetrahedra, whereas the formation of anorthite and diopside stabilized the pore morphology, resulting in regular circular pores. When MnO₂ was used as the foaming agent, the pressure from the gas produced during oxidation exceeded the surface tension of the molten phase owing to its viscosity, leading to the formation of larger, irregular, and interconnected pores. The foam ceramic material exhibited optimal properties when 2% CaCO₃ was used as the foaming agent, with a water absorption rate of 30%, bulk density of 0.62 g/cm³, porosity of 68.4%, compressive strength of 9.67 MPa, and thermal conductivity of 0.26 W/(m·K). Full article

(This article belongs to the Section Polycrystalline Ceramics)

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18 pages, 2524 KiB

Open AccessArticle

Measuring Optical Scattering in Relation to Coatings on Crystalline X-Ray Scintillator Screens

by Matthias Diez and Simon Zabler

Crystals 2025, 15(7), 605; https://doi.org/10.3390/cryst15070605 - 27 Jun 2025

Scattered light makes up a significant amount of recorded intensities during tomographic imaging, thereby leading to severe misinterpretation and artifacts in the reconstructed volume images. Correcting artificial intensities that stem from scattered light, therefore, is of primary interest and demands quantitative measurements. While [...] Read more.

Scattered light makes up a significant amount of recorded intensities during tomographic imaging, thereby leading to severe misinterpretation and artifacts in the reconstructed volume images. Correcting artificial intensities that stem from scattered light, therefore, is of primary interest and demands quantitative measurements. While numerous methods have been developed to reduce X-ray scattering artifacts, fewer methods deal with optical scattering. In this study, a measurement method for determining optical scattering in scintillators is presented with the aim of further developing correction algorithms. A theoretical model based on internal multiple reflections was developed for this purpose. This model assumes an additive exponential kernel with a certain scattering length to the system’s point spread function. This assumption was confirmed, and the scatter length was estimated from three new different kinds of experiments (hgap, rect, and LSF) on the BM18 beamline of the European synchrotron. The experiments further revealed significant differences in scattering proportion and length when different coatings are applied to the front and back faces of crystalline LuAG scintillators. Anti-reflective coatings on the backside show an effect of reducing the scattering magnitude while reflective coatings on the front side increase the proportion of the unscattered signal and, thus, show proportionally less scattering than black coating or no front coating. In particular, roughened black coating is found to worsen optical scattering. In summary, our results indicate that a combination of reflective (front) and anti-reflective (back) coatings yields the least optical scattering and, hence, the best image quality. Full article

(This article belongs to the Section Crystal Engineering)

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10 pages, 1703 KiB

Open AccessArticle

The Performance Degradation of Red, Green, and Blue Micro-LEDs Under High-Temperature Electrical Stress

by Changdong Tong, Yu Liu, Quan Deng, Li Pan, Guolong Chen, Yijun Lu, Tingzhu Wu, Zhong Chen and Weijie Guo

Crystals 2025, 15(7), 604; https://doi.org/10.3390/cryst15070604 - 27 Jun 2025

In this work, the degradation in luminous characteristics of red, green, and blue (RGB) micro-LEDs (10 µm × 10 µm) under electrical stress at 360 K has been investigated. After 280 h of aging, the AlGaInP-based red micro-LEDs exhibit a 31.7% reduction in [...] Read more.

In this work, the degradation in luminous characteristics of red, green, and blue (RGB) micro-LEDs (10 µm × 10 µm) under electrical stress at 360 K has been investigated. After 280 h of aging, the AlGaInP-based red micro-LEDs exhibit a 31.7% reduction in maximum external quantum efficiency, which is significantly greater than the reductions observed in InGaN-based green and blue micro-LEDs. Specifically, the peak wavelength redshift by 0.6 nm, and blueshift 1.0 nm, and 0.5 nm for RGB micro-LEDs, respectively. The color purity of green and blue micro-LEDs decreases by 3.6% and 0.7%, respectively, resulting in a 7% reduction in color gamut. Full article

(This article belongs to the Special Issue II-VI and III-V Semiconductors for Optoelectronic Devices)

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7 pages, 656 KiB

Open AccessCommunication

Cyclic Voltammetry and Micro-Raman Study of Graphene Oxide-Coated Silicon Substrates

by Grazia Giuseppina Politano

Crystals 2025, 15(7), 603; https://doi.org/10.3390/cryst15070603 - 27 Jun 2025

This work presents the improvement of the electro-optical response of n-type crystalline silicon via dip-coated graphene oxide (GO) thin films. GO was deposited on Si/SiO₂ by immersion, and the resulting heterostructures were characterized by cyclic voltammetry measurements and Raman spectroscopy. Raman analysis [...] Read more.

This work presents the improvement of the electro-optical response of n-type crystalline silicon via dip-coated graphene oxide (GO) thin films. GO was deposited on Si/SiO₂ by immersion, and the resulting heterostructures were characterized by cyclic voltammetry measurements and Raman spectroscopy. Raman analysis revealed a slight but measurable broadening (~0.7 cm⁻¹) of the Si TO phonon mode at 514 cm⁻¹, indicating local interfacial strain. Cyclic voltammetry measurements showed a substantial increase in photocurrent in comparison to pristine silicon substrates. These effects are attributed to a GO-induced p-type inversion layer and enhanced interfacial charge transfer. The results suggest that GO can serve as a functional interfacial layer for improving silicon-based optoelectronic and photoelectrochemical devices. Full article

(This article belongs to the Special Issue Optical Characterization of Functional Materials)

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14 pages, 2103 KiB

Open AccessArticle

Analysis of Fatigue Performance of Metallic Components with Gradient Microstructures

by Pandi Zhao, Liheng Tuo, Hongrui Zhang, Zhiyan Sun, Shuai Ren, Gaihuan Yuan and Zebang Zheng

Crystals 2025, 15(7), 602; https://doi.org/10.3390/cryst15070602 - 27 Jun 2025

Studying the fatigue performance of metallic components and optimizing their design from the perspectives of structure, microstructure, and service conditions has long been a critical research focus. In this study, a comprehensive analysis was conducted on the sealing performance and fatigue behavior of [...] Read more.

Studying the fatigue performance of metallic components and optimizing their design from the perspectives of structure, microstructure, and service conditions has long been a critical research focus. In this study, a comprehensive analysis was conducted on the sealing performance and fatigue behavior of W-shaped metallic sealing rings with varying microstructures. A novel simulation approach is proposed that replaces explicit gradient definitions with temperature conduction to address the issue of stress concentration at interfaces in the finite element modeling of gradient structures. Based on this method, a macroscopic finite element model was developed to simulate the plastic strain accumulation and springback of the sealing ring in service. Then, taking the stress evolution at the trough position of the sealing ring during service as a boundary condition, the evolution of stored-energy density and fatigue life of rings with different microstructures, including both homogeneous and gradient configurations, was quantitatively evaluated. The findings of this work provide valuable insights for the design of structural parameters and the optimization of forming process parameters in high-performance sealing-ring applications. Full article

(This article belongs to the Special Issue Crystallization of High Performance Metallic Materials (2nd Edition))

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13 pages, 2634 KiB

Open AccessArticle

Fabrication and Ultraviolet Response Characteristics of All-Oxide Bi₂O₃/Ga₂O₃ Heterojunction

by Xiuqing Cao, Fanxiang Wei, Jianwei Gu, Qingqing Zheng, Libin Wang and Zhenying Chen

Crystals 2025, 15(7), 601; https://doi.org/10.3390/cryst15070601 - 27 Jun 2025

Heterojunctions are commonly used in optoelectronic devices to improve device performance. However, interface defects and lattice mismatch often hinder carrier transport and reduce efficiency, emphasizing the need for further exploration of diverse heterojunction structures. In this study, a heterojunction device constructed from Bi [...] Read more.

Heterojunctions are commonly used in optoelectronic devices to improve device performance. However, interface defects and lattice mismatch often hinder carrier transport and reduce efficiency, emphasizing the need for further exploration of diverse heterojunction structures. In this study, a heterojunction device constructed from Bi₂O₃ and Ga₂O₃ is demonstrated. The microstructures and photoelectrical properties of Bi₂O₃ and Ga₂O₃ thin films were investigated. Bi₂O₃ and Ga₂O₃ thin films show a bandgap of 3.19 and 5.10 eV. The Bi₂O₃/Ga₂O₃ heterojunction-based device demonstrates rectification characteristics, with a rectification ratio of 2.72 × 10³ at ±4.5 V and an ON/OFF ratio of 1.07 × 10⁵ (4.5/−3.9 V). Additionally, we fabricated a sandwich-structured photodetector based on the Bi₂O₃/Ga₂O₃ heterojunction and investigated its ultraviolet photoresponse performance. The photodetector exhibits low dark current (0.34 pA @ −3.9 V) and fast response rise/fall time (<40/920 ms). This work offers important perspectives on the advancement of large-area, low-cost, and high-speed Bi₂O₃ film-based heterojunction photodetectors. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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11 pages, 3538 KiB

Open AccessArticle

Effect of Sm³⁺ Doping on Energy Storage Property and Thermal Stability of BaSn_xTi_1−xO₃ Ceramics

by Zhengchao Qin, Zhiyi Wang, Si Gao, Hongjuan Zheng, Jin Luo, Yunfei Liu and Yinong Lyu

Crystals 2025, 15(7), 600; https://doi.org/10.3390/cryst15070600 - 26 Jun 2025

Dielectric capacitors have become a key component for energy storage systems, owing to their exceptional power density and swift charge–discharge performance. In a series of lead-free ferroelectric ceramic materials, BaSn_xTi_1-xO₃ (BTS) received widespread attention due to its [...] Read more.

Dielectric capacitors have become a key component for energy storage systems, owing to their exceptional power density and swift charge–discharge performance. In a series of lead-free ferroelectric ceramic materials, BaSn_xTi_1-xO₃ (BTS) received widespread attention due to its unique properties. However, BTS ceramics with high Sn content have high efficiency (η) but low recovery energy storage density (W_rec). We incorporated the Sm element into BTS ceramics and aimed to optimize both efficiency and recoverable energy density at moderate Sn content. With the synergistic effect between Sm and Sn, the optimal composition was found at 5% Sn content with 1% low-level Sm dopants, where the energy storage density reached 0.2310 J/cm³ at 40 kV/cm. Furthermore, the thermal stability of the ceramic was investigated using temperature-dependent dielectric spectroscopy, in situ XRD, and temperature-dependent hysteresis loops. With Sm doping, the fluctuation of W_rec decreased from 18.48% to 12.01%. In general, this work not only enhances the understanding of samarium dopants but also proposes strategies for developing lead-free ferroelectric ceramics with superior energy storage properties. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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