Crystals

22 pages, 2440 KB

Open AccessArticle

Radiation-Induced Disorder and Lattice Relaxation in Gd₃Ga₅O₁₂ Under Swift Xe Ion Irradiation

by Zhakyp T. Karipbayev, Gulnara M. Aralbayeva, Abil T. Zhalgas, Kymbat Burkanova, Amangeldy M. Zhunusbekov, Ilze Manika, Abdirash Akilbekov, Aizat Bakytkyzy, Sergii Ubizskii, Gibrat E. Sagyndykova, Marina Konuhova, Anatolijs Sarakovskis, Yevheniia Smortsova and Anatoli I. Popov

Crystals 2025, 15(12), 1065; https://doi.org/10.3390/cryst15121065 - 18 Dec 2025

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Abstract

This study presents a comprehensive Raman spectroscopic and mechanical investigation of Gd₃Ga₅O₁₂ (GGG) single crystals irradiated with 231 MeV ¹³¹Xe ions at fluences ranging from 1 × 10¹¹ to 3.3 × 10¹³ ions/cm². [...] Read more.

This study presents a comprehensive Raman spectroscopic and mechanical investigation of Gd₃Ga₅O₁₂ (GGG) single crystals irradiated with 231 MeV ¹³¹Xe ions at fluences ranging from 1 × 10¹¹ to 3.3 × 10¹³ ions/cm². Raman analysis reveals that all fundamental vibrational modes of the garnet structure remain observable up to the highest fluence, with the preservation of garnet crystalline topology/absence of secondary crystalline phases. However, significant line broadening (FWHM increase by 20–100%) and low-frequency shifts indicate progressive lattice disorder and phonon-defect scattering. High-frequency Ga-O stretching modes (A_1g, T_2g ~740 cm⁻¹) remain the most resistant to irradiation, while low-energy translational modes involving Gd³⁺ ions exhibit pronounced degradation and partial disappearance at high fluence. Complementary nanoindentation measurements show radiation-induced softening: hardness decreases by up to ≈60% at 3.3 × 10¹³ ions/cm², consistent with amorphization and overlapping ion tracks (~10–12 μm deep). Raman spectroscopy shows that the garnet lattice remains as the only crystalline phase up to 3.3 × 10¹³ ions/cm², while significant line broadening, mode suppression and a strong hardness decrease indicate progressive structural disorder and partial amorphization of the near-surface region. These results demonstrate that GGG maintains crystalline integrity below the track-overlap threshold (~6 keV/nm) but undergoes strong structural relaxation and mechanical weakening once this limit is exceeded. A new analytical methodology has been developed to quantify radiation-induced structural degradation. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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16 pages, 4617 KB

Open AccessArticle

Enhancing the Electric Field-Induced Response of Graphene with Metal Oxides: Experimental and DFT Study

by Yuxing Lei, Bo Li, Mengyao Zhu, Jiao Sun and Haitao Yang

Crystals 2025, 15(12), 1064; https://doi.org/10.3390/cryst15121064 - 18 Dec 2025

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Abstract

The potential of graphene for electric field sensing is limited by its zero bandgap. This study employs a combined first-principles and experimental approach to enhance its response via heterojunctions with ZnO, SnO₂, and Al₂O₃. Calculations reveal spontaneous [...] Read more.

The potential of graphene for electric field sensing is limited by its zero bandgap. This study employs a combined first-principles and experimental approach to enhance its response via heterojunctions with ZnO, SnO₂, and Al₂O₃. Calculations reveal spontaneous formation and interfacial charge transfer in all systems, with SnO₂/graphene exhibiting the most significant charge transfer (0.3636 e) and inducing a finite bandgap (0.017–0.064 eV). Experimentally, SnO₂-graphene/PDMS composites demonstrated the highest relative permittivity (3.19) and a 7.76% increase in normalized induced voltage over pure PDMS within 50 Hz–50 kHz. This work establishes a direct correlation between interfacial charge transfer, bandgap opening, and macroscopic dielectric enhancement, identifying SnO₂/graphene as the optimal heterojunction. The integrated multi-scale methodology provides a clear design principle for high-performance, graphene-based field-sensitive materials. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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18 pages, 4000 KB

Open AccessArticle

Broadband Seismic Metamaterials Based on Gammadion-Shaped Chiral Structures

by Yawen Shen, Boyang Zhang, Pengcheng Ma, Qiujiao Du, Hongwu Yang, Pai Peng and Fengming Liu

Crystals 2025, 15(12), 1063; https://doi.org/10.3390/cryst15121063 - 18 Dec 2025

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Abstract

Controlling seismic wave propagation to protect critical infrastructure through metamaterials has emerged as a frontier research topic. The narrow bandgap and heavy weight of a resonant seismic metamaterial (SM) limit its application for securing buildings. In this research, we first develop a two-dimensional [...] Read more.

Controlling seismic wave propagation to protect critical infrastructure through metamaterials has emerged as a frontier research topic. The narrow bandgap and heavy weight of a resonant seismic metamaterial (SM) limit its application for securing buildings. In this research, we first develop a two-dimensional (2D) seismic metamaterial with gammadion-shaped chiral inclusions, achieving a high relative bandgap width of 77.34%. Its effective mass density is investigated to clarify the generation mechanism of the bandgap due to negative mass density between 12.53 and 28.33 Hz. Then, the gammadion-shaped pillars are introduced on a half-space to design a three-dimensional (3D) chiral SM to attenuate Rayleigh waves within a wider low-frequency range. Further, time-frequency analyses for real seismic waves and scaled experimental tests confirm the practical feasibility of the 3D SM. Compared with common resonant SMs, our chiral configurations offer a wider attenuation zone and lighter weight. Full article

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

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15 pages, 3499 KB

Open AccessArticle

Photothermal Heat Transfer in Nano-Hydroxyapatite/Carbon Nanotubes Composites Modeled Through Cellular Automata

by Cecilia Mercado-Zúñiga and José Antonio García-Merino

Crystals 2025, 15(12), 1062; https://doi.org/10.3390/cryst15121062 - 17 Dec 2025

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Abstract

Modeling elementary diffusion processes in nanostructured materials is essential for developing platforms capable of interacting with high-speed physical signals. In this work, the photothermal response of a nano-hydroxyapatite/carbon nanotube (nHAp/CNT) composite was experimentally characterized and modeled through a cellular automaton (CA) framework designed [...] Read more.

Modeling elementary diffusion processes in nanostructured materials is essential for developing platforms capable of interacting with high-speed physical signals. In this work, the photothermal response of a nano-hydroxyapatite/carbon nanotube (nHAp/CNT) composite was experimentally characterized and modeled through a cellular automaton (CA) framework designed to capture the thermal propagation of the hybrid system. Synthesizing nHAp/CNT composites enables the combination of the biocompatible and piezoelectric nature of nHAp with the enhanced photothermal response introduced by CNTs. UV–Vis reflectance measurements confirmed that CNT incorporation increases the optical absorption of the ceramic matrix, resulting in more efficient photothermal conversion. The composite was irradiated with a nanosecond pulsed laser, and the resulting thermal transients were compared with CA simulations based on a D2Q9 lattice configuration. The model accurately reproduces experiments, achieving R² > 0.991 and NRMSE below 2.4% for all tested laser powers. This strong correspondence validates the CA approach for predicting spatiotemporal heat diffusion in heterogeneous nanostructured composites. Furthermore, the model revealed a sensitive thermal coupling when two heat sources were considered, indicating synergistic enhancement of local temperature fields. These findings demonstrate both the effective integration of CNTs within the nHAp matrix and the capability of CA-based modeling to describe their photothermal behavior. Overall, this study establishes a computational–experimental basis for designing controlled thermal-wave propagation and guiding future multi-frequency or multi-source photothermal mixing experiments. Full article

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17 pages, 4795 KB

Open AccessArticle

Structural Diversity, Thermal, and Semiconducting Characteristics of Two N,N′-bis(phosphonomethyl)-1,4,5,8-Naphthalenediimide-Based Compounds

by Kenya V. Medina, Juan L. Pinedo, Kimberly P. Hernandez, Julian I. Ramirez, Callah Preti, Dimitrios Bourmas, Kenya Rosas, Ryan A. Flores, Josemaria S. Soriano, Hadi D. Arman and Pius O. Adelani

Crystals 2025, 15(12), 1061; https://doi.org/10.3390/cryst15121061 - 16 Dec 2025

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Abstract

Two crystals of N,N′-bis(phosphonomethyl)-1,4,5,8-naphthalenediimide were grown in the presence of neutral (water) and charged (imidazolium cation) species, yielding [(H₂O₃P)CH₂-(C₁₄H₄N₂O₄)-CH₂(PO₃H₂)]∙H₂O (1 [...] Read more.

Two crystals of N,N′-bis(phosphonomethyl)-1,4,5,8-naphthalenediimide were grown in the presence of neutral (water) and charged (imidazolium cation) species, yielding [(H₂O₃P)CH₂-(C₁₄H₄N₂O₄)-CH₂(PO₃H₂)]∙H₂O (1) and [C₃H₅N₂][(H_1.5O₃P)CH₂-(C₁₄H₄N₂O₄)-CH₂(PO₃H_1.5)] (2), respectively. The ligand N,N′-bis(phosphonomethyl)-1,4,5,8-naphthalenediimide was synthesized via the condensation of naphthalene-1,4,5,8-tetracarboxylic dianhydride with (aminomethyl)phosphonic acid in N,N′-dimethylformamide or imidazole. The flexible N-methyl phosphonic acid groups adopt a cis configuration in compound 1 and a trans configuration in compound 2. In compound 1, the phosphonate groups engage in extensive hydrogen bonding, as well as with water molecules and π–π stacking, resulting in a three-dimensional closely packed structure. Compound 2 forms a densely packed three-dimensional network stabilized by charge-assisted hydrogen bonding (anion-cation), anion–π interactions, and π–π stacking interactions. Hirshfeld surface analysis was conducted and the associated two-dimensional fingerprint plots were generated to further elucidate the nature and contributions of these noncovalent interactions. Direct bandgap measurements estimated from Tauc plots yielded values of 2.92 eV and 2.85 eV for compounds 1 and 2, respectively, highlighting their potential as promising n-type organic semiconductors. Thermal analysis reveals that compound 2 exhibits greater thermal stability than compound 1. Full article

(This article belongs to the Section Crystal Engineering)

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14 pages, 3483 KB

Open AccessArticle

The Influence of Annealing on the Structural, Optical and Electrical Properties of Copper Selenite Nanocrystals Synthesized by the Chemical Deposition Method

by Gulnaz Sarsekhan, Abay Usseinov, Aiman Akylbekova, Abdirash Akilbekov, Alma Dauletbekova, Diana Junisbekova, Ainash Abdrakhmetova, Gulnara Aralbayeva, Leila Kassenova and Zein Baimukhanov

Crystals 2025, 15(12), 1060; https://doi.org/10.3390/cryst15121060 - 14 Dec 2025

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Abstract

This work presents a study of copper selenite nanocrystals, obtained for the first time by chemical deposition (template synthesis) in a SiO₂/Si track template, and investigates their properties. The obtained nanostructures were subjected to structural, optical, and electrical analysis. After deposition, [...] Read more.

This work presents a study of copper selenite nanocrystals, obtained for the first time by chemical deposition (template synthesis) in a SiO₂/Si track template, and investigates their properties. The obtained nanostructures were subjected to structural, optical, and electrical analysis. After deposition, X-ray diffraction (XRD) analysis confirmed the formation of the orthorhombic phase CuSeO₃. Subsequent annealing in a vacuum at 800 °C and 1000 °C led to successive phase transformations: to the monoclinic phase and, finally, to the triclinic polymorph of copper selenite. Photoluminescence (PL) analysis showed that the intensity and spectral position of the emission peaks vary depending on the crystal structure, which is associated with changes in defects and bandgap width as a result of heat treatment. Current–voltage characteristic (CVC) measurements showed that the phase composition significantly affects electrical conductivity. In particular, the transition to the triclinic phase after annealing at 1000 °C led to noticeable changes in optical and electrical properties compared to the initial material. Thus, a direct relationship has been established between heat treatment conditions, crystal structure, and functional properties of CuSeO₃-based materials, opening up possibilities for their application in photonics and electronics. Full article

(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides Volume II)

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12 pages, 6047 KB

Open AccessArticle

Basic Concept of Purity Analysis of Facilities for High-Temperature Non-Oxide Crystal Growth

by Elena Voronina, Elena Mozhevitina, Karina Kim, Victoria Solomatina, Oleg Nefedov and Igor Avetissov

Crystals 2025, 15(12), 1059; https://doi.org/10.3390/cryst15121059 - 14 Dec 2025

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Abstract

The general procedure for measurement of impurities in hot zones of high-temperature growth setups is proposed and developed. In the first step, we prepared extra-pure 15 × 15 × 8 mm collecting cubes from composite graphite by high-temperature annealing in dry dynamic vacuum. [...] Read more.

The general procedure for measurement of impurities in hot zones of high-temperature growth setups is proposed and developed. In the first step, we prepared extra-pure 15 × 15 × 8 mm collecting cubes from composite graphite by high-temperature annealing in dry dynamic vacuum. The collecting cubes were placed in different parts of the hot zones of growth setups. We tested two types of crystal growth setups: single- and multi-crucible growth setups of a VGF configuration for A^IIIB^V semiconductors’ crystal growth. The hot zones of the setups were built from different types of graphite materials and high-temperature dielectric ceramics (BN and Al₂O₃) as insulators. The growth setups with collecting cubes without raw crystal materials were heated to operating temperatures, exposed for certain operating periods, and cooled to room temperature. The cubes were taken off and analyzed by extraction of condensed impurities into an analytic super-pure acid. The extracted impurities in the acid were determined by ICP-MS analysis. We showed that the hot zone of a single-crucible growth setup was nearly twice as pure (averaged 2.45 mg/g) compared with the hot zone of a multi-crucible setup (averaging 4.06 mg/g) because of the different graphite materials of the constructions. Full article

(This article belongs to the Section Industrial Crystallization)

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13 pages, 2273 KB

Open AccessArticle

The Effect of Electrolytic-Plasma Hardening Time on the Microstructure, Hardness, and Corrosion Behavior of Medium-Carbon Steel

by Yeldos Mukhametov, Aibek Shynarbek, Bauyrzhan Rakhadilov, Ainur Zhassulan, Nadir Ibragimov, Kuanysh Ormanbekov and Nurlat Kadyrbolat

Crystals 2025, 15(12), 1058; https://doi.org/10.3390/cryst15121058 - 13 Dec 2025

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Abstract

This study investigates the effect of electrolytic-plasma hardening time on the microstructure formation, hardness distribution, and corrosion behavior of grade 45 structural steel. The treatment was performed in a 15% aqueous sodium carbonate (Na₂CO₃) solution at an applied voltage [...] Read more.

This study investigates the effect of electrolytic-plasma hardening time on the microstructure formation, hardness distribution, and corrosion behavior of grade 45 structural steel. The treatment was performed in a 15% aqueous sodium carbonate (Na₂CO₃) solution at an applied voltage of 300 V for different holding times (8, 10, and 12 s). Scanning electron microscopy and X-ray diffraction analyses revealed that increasing the EPH duration promotes the formation of a more uniform martensitic layer and reduces the amount of residual cementite. Microhardness measurements showed an increase in surface hardness from 190 HV for the untreated steel to 770 HV after the longest treatment. The cross-sectional hardness profile indicated the presence of a thin decarburized sublayer and a zone of maximum hardness corresponding to the martensitic structure. Potentiodynamic polarization tests in a 0.5 M NaCl solution showed a slight increase in corrosion current density after treatment; however, the corrosion rate remained within the range of 0.19–0.45 mm year⁻¹, confirming the satisfactory corrosion resistance of the hardened layer. The results demonstrate that controlling the EPH duration allows for optimizing the balance between enhanced hardness and maintained corrosion resistance of grade 45 steel. Full article

(This article belongs to the Special Issue Crystallization of High-Performance Metallic Materials (3rd Edition))

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13 pages, 6289 KB

Open AccessArticle

Chemical Composition and Ultrastructure of Bone Apatite in Initial Osteoporosis: Mineralogical Study

by Artem A. Bibko, Oksana V. Bukharova, Roman Yu. Shendrik, Henry P. Schwarcz, Dmitry V. Lychagin and Evgeni A. Kostrub

Crystals 2025, 15(12), 1057; https://doi.org/10.3390/cryst15121057 - 13 Dec 2025

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Abstract

Bone is one of the most important organs of mammals, consisting of collagen and apatite. Various diseases, such as osteoporosis, can affect the components of bone tissue, their chemical composition and bone ultrastructure, which leads to changes in properties. In this paper, the [...] Read more.

Bone is one of the most important organs of mammals, consisting of collagen and apatite. Various diseases, such as osteoporosis, can affect the components of bone tissue, their chemical composition and bone ultrastructure, which leads to changes in properties. In this paper, the effect of initial osteoporosis on the chemical composition of bone apatite and the ultrastructure of bone tissue from a mineralogical point of view is analyzed using rat femurs as an example. The chemical composition of bone apatite was studied using SEM, EDS and FTIR-ATR spectroscopy. The bone ultrastructure was examined using a transmission electron microscope. An increase in the content of carbonate ion in the position of the phosphorus group and a change in the orientation of apatite crystals inside mineral plates were revealed against the background of initial osteoporosis, which can affect not only the mechanical properties of bone, but also the stability of apatite under biological conditions. Full article

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

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16 pages, 2777 KB

Open AccessArticle

The Pressure Response of Bulk and Two−Dimensional MoS₂ Crystals Studied by Raman and Photoluminescence Spectroscopy: Dimensionality and Pressure Transmitting Medium Effects

by Niki Sorogas, Krystallis Tersis, Antonios Michail, Sotirios Ves, Konstantinos Papagelis, Dimitrios Christofilos and John Arvanitidis

Crystals 2025, 15(12), 1056; https://doi.org/10.3390/cryst15121056 - 12 Dec 2025

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Abstract

The pressure response of bulk and two−dimensional (2D) MoS₂ crystals (monolayer, bilayer, and many–layered), directly transferred to the diamond surface of the diamond anvil cell (DAC) used for high−pressure application, is examined by means of Raman and photoluminescence (PL) spectroscopy. For the [...] Read more.

The pressure response of bulk and two−dimensional (2D) MoS₂ crystals (monolayer, bilayer, and many–layered), directly transferred to the diamond surface of the diamond anvil cell (DAC) used for high−pressure application, is examined by means of Raman and photoluminescence (PL) spectroscopy. For the high–pressure experiments of 2D MoS₂, the Daphne 7474 oil and the 4:1 methanol–ethanol mixture are alternatively used as pressure-transmitting media (PTM), while the former is also used as PTM in the case of bulk MoS₂. Characteristic differences are observed in the pressure evolution of the Raman spectral profile and the pressure coefficients of the peak frequencies between the bulk and the 2D MoS₂ crystals of various thicknesses, which also depend on the PTM used. These observations, along with the pressure evolution of the PL spectrum of 2D MoS₂, are ascribed to the different stress conditions in each case (hydrostatic vs. uniaxial compression perpendicular to the MoS₂ layers), the adhesion of the 2D MoS₂ crystals on the diamond anvil, as well as the nature of the particular PTM used and its interaction with the studied system. Full article

(This article belongs to the Special Issue Recent Advances in Graphene and Other Two-Dimensional Materials)

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14 pages, 1799 KB

Open AccessArticle

Wide-Temperature-Range Optical Thermometry Based on Yb³⁺,Er³⁺:CaYAlO₄ Phosphor

by Shaozhen Lv, Shaobo Yao and Zhuohong Feng

Crystals 2025, 15(12), 1055; https://doi.org/10.3390/cryst15121055 - 12 Dec 2025

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Abstract

In order to meet the demand for new optical temperature-sensing materials with high sensitivity and a wide application temperature range, Yb³⁺/Er³⁺: CaYAlO₄ phosphor with excellent physical and chemical stability and thermal conductivity was studied for the first time. [...] Read more.

In order to meet the demand for new optical temperature-sensing materials with high sensitivity and a wide application temperature range, Yb³⁺/Er³⁺: CaYAlO₄ phosphor with excellent physical and chemical stability and thermal conductivity was studied for the first time. Yb³⁺/Er³⁺: CaYAlO₄ phosphors have been synthesized by the high-temperature solid-state method. Under 980 nm excitation, three characteristic emission bands peaking at 528, 549 and 665 nm were observed which are attributed to the transitions ²H_11/2, ⁴S_3/2 and ⁴F_9/2 to ⁴I_15/2, respectively. The temperature-sensing behaviors of the phosphor were investigated using the luminescence intensity ratio technique based on both the TCL (²H_11/2/⁴S_3/2) and NTCL (⁴F_9/2/⁴S_3/2, ²H_11/2/⁴F_9/2) model over a wide temperature range of 163–700 K. The maximum relative sensitivities of TCLs (²H_11/2/⁴S_3/2), NTCLs (⁴F_9/2/⁴S_3/2) and NTCLs (²H_11/2/⁴F_9/2) were 3.69% K⁻¹, 0.443% K⁻¹ and 3.86% K⁻¹ at 163 K, 275 K and 163 K, while the maximum absolute sensitivities were 4.04 × 10⁻³ K⁻¹, 15.2 × 10⁻³ K⁻¹ and 7.81 × 10⁻⁴ K⁻¹ at 499 K, 499 K and 247 K, respectively. Results suggest that Yb³⁺/Er³⁺: CaYAlO₄ phosphor is a promising temperature-measuring material with advanced optical sensing capabilities over a wide temperature range. Full article

(This article belongs to the Special Issue Rare Earth-Based Crystalline Materials: Synthesis, Characterization and Applications)

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22 pages, 12895 KB

Open AccessArticle

The Role of Rotational Tool Speed in the Joint Performance of AA2024-T4 Friction Stir Spot Welds at a Short 3-Second Dwell Time

by Yousef G. Y. Elshaghoul, Mahmoud F. Y. Shalaby, Mohamed M. El-Sayed Seleman, Ahmed Elkelity, Hagar A. Reyad and Sabbah Ataya

Crystals 2025, 15(12), 1054; https://doi.org/10.3390/cryst15121054 - 12 Dec 2025

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Abstract

This study explores Friction Stir Spot Welding (FSSW), a well-established solid-state joining technique, for high-strength aluminum alloys like AA2024-T4, which present significant challenges for conventional welding techniques. This research focuses on the impact of relatively low rotational speeds, specifically within a range of [...] Read more.

This study explores Friction Stir Spot Welding (FSSW), a well-established solid-state joining technique, for high-strength aluminum alloys like AA2024-T4, which present significant challenges for conventional welding techniques. This research focuses on the impact of relatively low rotational speeds, specifically within a range of 700 to 1300 rpm, on the mechanical and microstructural properties of the welded joints. By employing a short dwell time of 3 s, this study aims to enhance productivity in the automotive and aerospace industries. The experimental work evaluated the joints’ thermal cycles, macrostructure, microstructure, hardness and load-carrying capacity. Results indicated a linear relationship between rotational speed and heat input. Although all welds exhibited a significant grain size reduction in the stir zone (SZ) compared to the base material (29.7 ± 6.1 μm), the SZ grain size increased with rotational speed, ranging from 4.7 ± 1.4 to 8.3 ± 1.3 μm. This study identified 900 rpm as the optimal parameter, achieving the highest load-carrying capacity (7.35 ± 0.4 kN) and a high SZ hardness (99 ± 1.5 HV). These findings confirm that joint strength is a balance between grain refinement and thermal softening. The presence of precipitates and the fractography of the tensile–shear tested specimens were also investigated and discussed. Full article

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

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18 pages, 20231 KB

Open AccessArticle

In Situ Alloying of Ti-6Al-7Nb with Copper Using Laser Powder Bed Fusion

by Paul Steinmeier, Kay-Peter Hoyer, Nelson Filipe Lopes Dias, Reiner Zielke, Wolfgang Tillmann and Mirko Schaper

Crystals 2025, 15(12), 1053; https://doi.org/10.3390/cryst15121053 - 12 Dec 2025

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Abstract

Titanium alloys are widely employed for biomedical implants due to their high strength, biocompatibility, and corrosion resistance, yet their lack of intrinsic antibacterial activity remains a major limitation. Incorporating copper, an antibacterial and β-stabilising element, offers a promising strategy to enhance implant performance. [...] Read more.

Titanium alloys are widely employed for biomedical implants due to their high strength, biocompatibility, and corrosion resistance, yet their lack of intrinsic antibacterial activity remains a major limitation. Incorporating copper, an antibacterial and β-stabilising element, offers a promising strategy to enhance implant performance. This study investigates Ti-6Al-7Nb modified with 1–9 wt.% Cu via in situ alloying during metal-based laser powder bed fusion (PBF-LB/M), with the aim of assessing processability, microstructural evolution, and mechanical properties. Highly dense samples (>99.9%) were produced across all Cu levels, though chemical homogeneity strongly depended on processing parameters. Increasing Cu content promoted β-phase stabilisation, Ti₂Cu precipitation, and pronounced grain refinement. Hardness and yield strength increased nearly linearly with Cu addition, while ductility decreased sharply at ≥5 wt.% Cu due to intermetallic formation, hot cracking, and brittle fracture. These results illustrate both the opportunities and constraints of rapid alloy screening via PBF-LB/M. Overall, moderate Cu additions of 1–3 wt.% provide the most favourable balance between mechanical performance, manufacturability, and potential antibacterial functionality. These findings provide a clear guideline for the design of Cu-functionalised titanium implants and demonstrate the efficiency of in situ alloy screening for accelerated materials development. Full article

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

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17 pages, 10887 KB

Open AccessArticle

The Effect of Bulk Nucleation Parameters on the Solidification Structure of Large Slabs During Electroslag Remelting and Optimization of Production Process Parameters

by Qi Li, Yu Du, Zhenquan Jing and Yanhui Sun

Crystals 2025, 15(12), 1052; https://doi.org/10.3390/cryst15121052 - 11 Dec 2025

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Abstract

In this paper, the moving heat transfer boundary method is adopted to establish a three-dimensional solidification microstructure model based on the coupling technology of the cellular automata method (CA) and finite element method (FE), simulate the ingot growth process, and optimize the nucleation [...] Read more.

In this paper, the moving heat transfer boundary method is adopted to establish a three-dimensional solidification microstructure model based on the coupling technology of the cellular automata method (CA) and finite element method (FE), simulate the ingot growth process, and optimize the nucleation parameters. In addition, this study also explored the influence of process parameters such as melting rate, molten pool temperature, and cooling intensity on the solidification structure of ingots, providing a theoretical basis for process optimization. The results show that the maximum nucleation undercooling degree and the maximum nucleation density have significant effects on different crystal regions of the ingot solidification structure, while the maximum nucleation variance has no obvious effect on the changes in the solidification structure. When the maximum bulk nucleus undercooling degree

{Δ T}_{v, \max}

= 4 K, the bulk nucleus standard deviation

{Δ T}_{v, σ}

= 5 K, and the maximum bulk nucleus density

n_{v, \max}

= 3 × 107, the simulation results of the solidification structure can be well consistent with the experimental results. With the increase in smelting speed, the number of grains in the ingot structure gradually increases, while the average area of grains gradually decreases. The melting temperature and the intensity of side wall cooling have no obvious influence on the solidification structure of the ingot. Full article

(This article belongs to the Special Issue Crystallization of High-Performance Metallic Materials (3rd Edition))

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26 pages, 11542 KB

Open AccessArticle

The Comparative Study of Four Hexachloroplatinate, Tetrachloroaurate, Tetrachlorocuprate, and Tetrabromocuprate Benzyltrimethylammonium Salts: Synthesis, Single-Crystal X-Ray Structures, Non-Classical Synthon Preference, Hirshfeld Surface Analysis, and Quantum Chemical Study

by Joanna Bojarska, Martin Breza, Ingrid Jelemenska, Izabela D. Madura, Sepideh Jafari, Damian Trzybiński, Krzysztof Woźniak and Adam Mieczkowski

Crystals 2025, 15(12), 1051; https://doi.org/10.3390/cryst15121051 - 11 Dec 2025

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Abstract

Four benzyltrimethylammonium (BTMA) salts were successfully prepared: bis(benzyltrimethylammonium) hexachloroplatinate (1), benzyltrimethylammonium tetrachloroaurate (2), bis(benzyltrimethylammonium) tetrachlorocuprate (3), and bis(benzyltrimethylammonium) tetrabromocuprate (4) from benzyltrimethylammonium hydroxide (Triton B). Their crystal structures were determined by single-crystal X-ray diffraction, and [...] Read more.

Four benzyltrimethylammonium (BTMA) salts were successfully prepared: bis(benzyltrimethylammonium) hexachloroplatinate (1), benzyltrimethylammonium tetrachloroaurate (2), bis(benzyltrimethylammonium) tetrachlorocuprate (3), and bis(benzyltrimethylammonium) tetrabromocuprate (4) from benzyltrimethylammonium hydroxide (Triton B). Their crystal structures were determined by single-crystal X-ray diffraction, and the supramolecular architectures were characterized hierarchically. Extended Hirshfeld surface analysis, including enrichment ratio calculations, was performed to evaluate intermolecular interactions. Nonclassical hydrogen bonds, such as C–H^…Cl(Br), involving the anions, contribute to the formation of self-assembled architectures. Additional stabilization arises from π^…π and Cu–Br^…π interactions, particularly in crystals 2 and 4, respectively. Hirshfeld surface analysis showed that H^…H and C^…H/H^…C interactions are the dominant contributors in all crystals. According to enrichment ratio calculations, C^…H/H^…C interactions in 1, 3, and 4; Cl^…H/H^…Cl in 1 and 3; Cu^…H/H^…Cu in 3 and 4; and Br^…H/H^…Br and Br^…C/C^…Br in 4 are statistically favored in the crystal packing. Halogen bonding Cl^…Cl was observed in 1 but does not significantly influence packing. Energy framework calculations indicated that dispersive interactions are favorable in the analyzed crystals. A library of H-bonding supramolecular patterns, including interchangeable synthons, is provided and may guide the rational design of new derivatives with controllable features. Finally, the topology of intermolecular connections and the electronic structure of the benzyltrimethylammonium cation, investigated by quantum-chemical calculations, provide insights into its reactivity. Full article

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18 pages, 4921 KB

Open AccessArticle

Multi-State Photoluminescence of Donor–π–Acceptor Tetrafluorinated Tolane Mesogenic Dimers in Solution, Crystal, and Liquid-Crystalline Phases

by Sorato Inui, Yuto Eguchi, Masato Morita, Motohiro Yasui, Tsutomu Konno and Shigeyuki Yamada

Crystals 2025, 15(12), 1050; https://doi.org/10.3390/cryst15121050 - 11 Dec 2025

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Abstract

Photoluminescent liquid crystals with photoluminescence (PL) and liquid-crystalline (LC) properties have attracted attention as PL-switching materials owing to their thermally induced phase transitions, such as crystal → smectic A/nematic → isotropic phase transitions. Our group previously developed tetrafluorinated tolane mesogenic dimers linked by [...] Read more.

Photoluminescent liquid crystals with photoluminescence (PL) and liquid-crystalline (LC) properties have attracted attention as PL-switching materials owing to their thermally induced phase transitions, such as crystal → smectic A/nematic → isotropic phase transitions. Our group previously developed tetrafluorinated tolane mesogenic dimers linked by flexible alkylene-1,n-dioxy spacers, demonstrating that the position of the tetrafluorinated aromatic ring critically influences the LC behavior. However, these compounds exhibited very weak fluorescence owing to an insufficient D–π–A character of the π-conjugated mesogens, which facilitated internal conversion from emissive ππ* to non-emissive πσ* states. We designed and synthesized derivatives in which the mesogen–spacer linkage was modified from ether to ester, thereby enhancing the D–π–A character. Thermal and structural analyses revealed spacer-length parity effects: even-numbered spacers induced nematic phases, whereas odd-numbered spacers stabilized smectic A phases. Photophysical studies revealed multi-state PL across solution, crystal, and LC phases. Strong blue PL (Φ_PL = 0.39–0.48) was observed in solution, while crystals exhibited aggregation-induced emission enhancement (Φ_PL = 0.48–0.77) with spectral diversity. In LC states, Φ_PL values up to 0.36 were maintained, showing reversible intensity and spectral shifts with phase transitions. These findings establish design principles that correlate spacer parity, phase behavior, and PL properties, enabling potential applications in PL thermosensors and responsive optoelectronic devices. Full article

(This article belongs to the Section Liquid Crystals)

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10 pages, 2311 KB

Open AccessArticle

CVD-Grown Carbon Nanofibers on Knitted Carbon Fabric for Enhanced Supercapacitor Performance

by Xiaojing Jia, Jiangsan Wang and Jing Dang

Crystals 2025, 15(12), 1049; https://doi.org/10.3390/cryst15121049 - 11 Dec 2025

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Abstract

The escalating demand for high-performance energy storage devices has driven extensive research into flexible electrode materials for supercapacitors. Integrating structured carbon nanomaterials with flexible substrates to construct binder-free electrode architectures represents a promising strategy for improving supercapacitor capacitance and rate capability. However, achieving [...] Read more.

The escalating demand for high-performance energy storage devices has driven extensive research into flexible electrode materials for supercapacitors. Integrating structured carbon nanomaterials with flexible substrates to construct binder-free electrode architectures represents a promising strategy for improving supercapacitor capacitance and rate capability. However, achieving stable, binder-free integration of structure-controlled nanostructured carbon materials with flexible substrates remains a critical challenge. In this study, we report a direct synthesis approach for one-dimensional (1D) carbon nanofibers (CNFs) on commercial flexible carbon fabric (CF) via chemical vapor deposition (CVD). The resulting CNFs exhibit two typical average diameters—approximately 25 nm and 50 nm—depending on the growth temperature, with both displaying highly graphitized structures. Electrochemical characterization of the CNFs/CF composites in 1 M H₂SO₄ electrolyte revealed typical electric double-layer capacitor (EDLC) behavior. Notably, the 25 nm-CNFs/CF electrode achieves a high specific capacitance of 87.5 F/g, significantly outperforming the 50 nm-CNFs/CF electrode, which reaches 50.2 F/g. Compared with previously reported carbon nanotube CNTs/CF electrodes, the 25 nm-CNFs/CF electrode exhibits superior capacitance and lower resistance. Full article

(This article belongs to the Special Issue Advanced Catalytic Materials in Energy and Environment)

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15 pages, 5335 KB

Open AccessArticle

Autoclave Expansion and Compressive Strength of MgO-Admixed RCC with Partial Fly Ash Replacement by Phosphorus Slag

by Rongfei Chen and Changli Chen

Crystals 2025, 15(12), 1048; https://doi.org/10.3390/cryst15121048 - 11 Dec 2025

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Abstract

High-volume fly ash (FA) mitigates the expansion of magnesium oxide (MgO), and the uneven regional distributions of high-quality FA collectively limit the application of roller-compacted concrete admixed with MgO (M-RCC). This study evaluated the autoclave expansion and compressive strength of MgO-admixed cement paste [...] Read more.

High-volume fly ash (FA) mitigates the expansion of magnesium oxide (MgO), and the uneven regional distributions of high-quality FA collectively limit the application of roller-compacted concrete admixed with MgO (M-RCC). This study evaluated the autoclave expansion and compressive strength of MgO-admixed cement paste and mortar, wherein phosphorus slag (PS) was used to partially or fully replace FA. The expansion mechanism within the MgO-FA-PS system was explored. Results show that the autoclave expansion of the mortar increased as the proportion of PS replacing FA rose. At a replacement ratio of 33% (i.e., 20% of the total mass of cementitious materials), the mortar maintained the same ultimate MgO dosage (8%) as the control specimen, yet exhibited a 12.7% increase in expansion and an 8.8% decrease in strength. The mechanism is that PS is less efficient than FA in reducing the pore solution alkalinity, thereby promoting the formation of more brucite. The growth pressure of brucite crystals expands the internal gaps in the matrix and coarsens the pore size, resulting in greater expansion and reduced compressive strength. The results of this study can provide theoretical and technical insights for the application of PS in M-RCC. Full article

(This article belongs to the Special Issue Synergizing Crystallography, Mineral Materials Science and Solid Waste Upcycling for Sustainable Materials Innovation)

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13 pages, 1825 KB

Open AccessArticle

Spectral-Based Temperature Sensing in Cr:LiCAF Crystals Using Fluorescence Peak Shift Calibration

by Yusuf Öztürk

Crystals 2025, 15(12), 1047; https://doi.org/10.3390/cryst15121047 - 9 Dec 2025

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Abstract

In this study, we present a non-invasive and contactless method for estimating the internal temperature of Cr:LiCAF laser crystals using temperature-dependent shifts in fluorescence emission peaks. A high-resolution calibration dataset was created with 181 spectral points from 10 to 100 °C. Linear regression [...] Read more.

In this study, we present a non-invasive and contactless method for estimating the internal temperature of Cr:LiCAF laser crystals using temperature-dependent shifts in fluorescence emission peaks. A high-resolution calibration dataset was created with 181 spectral points from 10 to 100 °C. Linear regression yielded a temperature estimation model with an R² of 0.73, which was validated under both lasing and non-lasing conditions. To further evaluate the reliability of this optical thermometry method, thermal imaging data from a FLIR E75 infrared camera were incorporated. Surface temperatures measured at various diode current levels closely matched the internal temperature predictions based on fluorescence shifts (MAE = 0.775 °C, R² = 0.993), confirming the robustness of the method. This dual-approach validation enhances confidence in using fluorescence-based diagnostics for real-time thermal monitoring in laser systems. The combined use of spectrometer-based and thermal camera measurements suggests potential for hybrid diagnostics in laser research and development, offering improved thermal feedback for optimizing high-power laser performance. Full article

(This article belongs to the Special Issue Research Progress of Laser Crystals)

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19 pages, 7771 KB

Open AccessArticle

Research on the Hot Deformation Behavior and Mechanism of a New Nickel-Based P/M Superalloy

by Yifan Liu, Yanhui Yang, Jie Yang, Yaliang Zhu, Xiaofeng Wang, Weiwei Xia, Xianghui Meng and Kelu Zhong

Crystals 2025, 15(12), 1046; https://doi.org/10.3390/cryst15121046 - 8 Dec 2025

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Abstract

Based on hot-compression simulations combined with SEM and TEM analyses, the high-temperature deformation behavior and mechanisms of a new nickel-based powder superalloy FGH101 were investigated over 1020–1110 °C and strain rates of 0.001–0.05 s⁻¹. From the experimental data, the variations in [...] Read more.

Based on hot-compression simulations combined with SEM and TEM analyses, the high-temperature deformation behavior and mechanisms of a new nickel-based powder superalloy FGH101 were investigated over 1020–1110 °C and strain rates of 0.001–0.05 s⁻¹. From the experimental data, the variations in the strain-rate sensitivity index m, the apparent activation energy for hot deformation Q, and the grain-size exponent p were determined as functions of strain rate and temperature. Hot deformation processing maps and mechanism maps incorporating dislocation density were established. The processing maps clearly revealed the evolution of formable regions at different temperatures and strains, while the mechanism maps successfully predicted the dislocation evolution and its operative hot deformation mechanisms by introducing the grain size evolution corrected by Burgers-vector compensation and the rheological flow stress behavior compensated by the modulus. The results indicated an optimal processing window of 1060–1100 °C at 0.001–0.003 s⁻¹. Within the tested regime, as the strain rate decreased, the operative mechanism for grain-boundary sliding transitioned from pipe-diffusion control to lattice-diffusion control. These findings provide a solid theoretical basis for the design and optimization of the isothermal forging process of the new FGH101 alloy. Full article

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

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18 pages, 2839 KB

Open AccessArticle

Experiments and Simulations for Reactive Crystallization of Li₃PO₄ from Low Concentration Li-Rich Brine

by Jie Fan, Wanxia Ma, Xiaoxiang He, Guowang Xu, Zhenghua He, Chaoliang Zhu, Yifei Shi, Bo Li and Xiaochuan Deng

Crystals 2025, 15(12), 1045; https://doi.org/10.3390/cryst15121045 - 8 Dec 2025

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Abstract

Li₃PO₄ is an ideal precursor for synthesizing high-performance LiFePO₄, as it simultaneously provides lithium and phosphorus sources. Extremely low solubility of Li₃PO₄ enables efficient lithium recovery from low-concentration Li-rich brine by reactive crystallization. A focused [...] Read more.

Li₃PO₄ is an ideal precursor for synthesizing high-performance LiFePO₄, as it simultaneously provides lithium and phosphorus sources. Extremely low solubility of Li₃PO₄ enables efficient lithium recovery from low-concentration Li-rich brine by reactive crystallization. A focused beam reflectance measurement (FBRM) system was employed to monitor the key optimization parameters for Li₃PO₄ crystallization, supersolubility, and metastable zone widths (MSZWs). The optimized process parameters were determined by systematically investigating the effects of operating conditions. Additionally, prediction of supersolubility and MSZWs was accomplished with theoretical models. Results demonstrate that both supersolubility and MSZWs exhibit a pronounced negative correlation with temperature. Supersolubility decreased sharply when LiCl concentration exceeded 5 mol·L⁻¹ or Na₃PO₄ concentration surpassed 0.8 mol·L⁻¹. Conversely, it increased exponentially with Na₃PO₄ feeding rate. The effect of impurity (NaCl/KCl) was non-monotonic, initially increasing and then decreasing supersolubility and MSZWs. Among these, Na₂B₄O₇ most significantly enhanced both parameters, followed by Na₂SO₄. The supersolubility data were well-fitted by an empirical equation (R² > 0.99). For MSZWs prediction, the self-consistent Nývlt-like model (R² > 0.9883) and the modified Sangwal’s model (R² > 0.994) achieved superior performance. Collectively, these findings establish a theoretical basis for optimizing lithium recovery via Li₃PO₄ crystallization, facilitating more efficient and sustainable production of high-purity lithium products. Full article

(This article belongs to the Section Crystal Engineering)

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16 pages, 5950 KB

Open AccessArticle

Near-Ms Austempering of Carbide-Free Bainitic Steel: Effects on Phase Transformation, Microstructure and Mechanical Properties

by Haoqing Zheng, Zhixiang Liu, Hua Fan, Xiao Hu, Guanqiao Su, Yang Jin, Hongwei Wang, Tao Xie and Xuefei Huang

Crystals 2025, 15(12), 1044; https://doi.org/10.3390/cryst15121044 - 8 Dec 2025

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Abstract

The parameters of the austempering process play a crucial role in governing the microstructure and mechanical properties of carbide-free bainitic (CFB) steel. In this study, a CFB steel was austempered at temperatures close to its martensite start (Ms = 372 °C) temperature to [...] Read more.

The parameters of the austempering process play a crucial role in governing the microstructure and mechanical properties of carbide-free bainitic (CFB) steel. In this study, a CFB steel was austempered at temperatures close to its martensite start (Ms = 372 °C) temperature to investigate the bainitic transformation kinetics, microstructure, and mechanical properties. To identify the optimal strength–ductility combination, austempering was carried out at 360 °C, 380 °C, and 400 °C for comparison. The results show that austempering slightly below Ms (360 °C) produces the highest yield-to-tensile strength ratio and a good strength–ductility balance. Dilatometry curves indicate that the onset of bainite transformation occurs fastest when austempering slightly below Ms. The stronger transformation driving force and the presence of athermal martensite are the primary reasons. The enhanced thermodynamic driving force and increased nucleation density promote the formation of a larger amount of bainitic laths. Electron backscatter diffraction (EBSD) analysis reveals that the retained austenite blocks are finest after austempering at 360 °C, which helps alleviate the ductility loss associated with the reduction in retained austenite content. Full article

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

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14 pages, 2697 KB

Open AccessArticle

Comparative Analysis of Physicochemical Properties for Three Crystal Forms of Cordycepin and Their Interconversion Relationship

by Wenbo Li, Shushu Li, Qingshi Wen, Xiaohan Zhang, Ke Zhang, Chenglun Tang, Fengxia Zou, Keke Zhang, Pengfei Jiao and Pengpeng Yang

Crystals 2025, 15(12), 1043; https://doi.org/10.3390/cryst15121043 - 6 Dec 2025

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Abstract

Cordycepin (3′-deoxyadenosine, 3′-dA), the flagship nucleoside antibiotic from Cordyceps militaris, exerts potent anti-inflammatory, antimicrobial, and antitumor activity but is rapidly inactivated by human adenosine deaminase (ADA). While prodrugs, ADA inhibitors, and nanocarriers have been pursued to prolong its half-life, the influence of solid [...] Read more.

Cordycepin (3′-deoxyadenosine, 3′-dA), the flagship nucleoside antibiotic from Cordyceps militaris, exerts potent anti-inflammatory, antimicrobial, and antitumor activity but is rapidly inactivated by human adenosine deaminase (ADA). While prodrugs, ADA inhibitors, and nanocarriers have been pursued to prolong its half-life, the influence of solid form on delivery performance remains unexplored. Here, three polymorphs—anhydrate-I (flake-like), anhydrate-II (rod-like), and a previously unreported monohydrate (fibrillar)—were prepared, characterized (PXRD, TG-DSC, FTIR), and subjected to equilibrium solubility, slurry-conversion, and humidity-sorption mapping. The monohydrate dehydrates at 144 °C and sequentially transforms to anhydrate-I → anhydrate-II (ΔH = −127.5 J g⁻¹), establishing a monotropic relationship between the two anhydrous forms. Solubility displays a bell-shaped profile versus water activity: the monohydrate is stable above aw 0.8, whereas anhydrate-II predominates below aw 0.2. In model immediate-release tablets, anhydrate-II achieves complete dissolution within 10 min, whereas the monohydrate sustains release for 30 min. Hygroscopicity tests show the monohydrate absorbs <6% water up to 75% RH without structural change, whereas anhydrate-I converts to the monohydrate above 63% RH. The quantitative humidity–crystal form–performance correlations provide a rational platform for crystal form selection and the design of stable, efficacious cordycepin solid dosage forms. Full article

(This article belongs to the Section Crystal Engineering)

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14 pages, 3346 KB

Open AccessArticle

Gemological and Spectral Characteristics of Andradite Garnets with Usambara Effect from Yuanjiang in Yunnan Province

by Liu-Run-Xuan Chen, Yi-Min Tian, Shi-Tao Zhang, Zhi Qu, Hong-Tao Shen, Xiao-Qi Yang and Yun-Ke Zheng

Crystals 2025, 15(12), 1042; https://doi.org/10.3390/cryst15121042 - 5 Dec 2025

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Abstract

Yuanjiang County is one of the most important gem-producing areas in China. The authors of this study discovered and collected gem-quality andradite Garnsts in the epidote amphibolite from the periphery of the ruby deposit in Shaku Village, Yuanjiang County. After careful observation of [...] Read more.

Yuanjiang County is one of the most important gem-producing areas in China. The authors of this study discovered and collected gem-quality andradite Garnsts in the epidote amphibolite from the periphery of the ruby deposit in Shaku Village, Yuanjiang County. After careful observation of the collected andradite, it was found that these andradite samples appear green when the thickness is less than 2 mm and reddish-brown when the thickness is greater than 2 mm, exhibiting the typical Usambara effect. To investigate the gemological and spectroscopic characteristics of Yuanjiang andradite, this study conducted basic gemological tests, microscopic observation, electron probe microanalysis (EPMA), ultraviolet–visible (UV-Vis) absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and laser Raman spectroscopy on the collected samples. Tests show that Yuanjiang andradite has a lower specific gravity than typical andradite, which is due to the presence of epidote inclusions inside. EPMA results indicate that the samples contain a certain amount of Cr element. The crystal chemical formula of the samples calculated from the EPMA results is (Ca_2.89–2.93, Mn_0.01–0.02, Fe_0.15–0.10)(Fe_1.69–1.95, Al_0.00–0.23, Cr_0.00–0.23, Si_0.05–0.08)(SiO₄)₃. UV-Vis tests show that the samples have transmission windows in both the green- and red-light regions, with Fe³⁺ and Cr³⁺ acting as the main chromogenic ions, among which Cr³⁺ is crucial for the occurrence of the Usambara effect. The FTIR and Raman test results are basically the same as previous research results, but some peak positions related to metal cations differ from the theoretical values, which may be caused by the presence of a certain amount of Cr³⁺ in the samples. Full article

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

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17 pages, 3597 KB

Open AccessArticle

Analysis of the Role of Fly Ash and Calcium Hydroxide in Synergistically Regulating the Fluidity, Setting, and Strength of Alkali-Activated Slag

by Guodong Huang, Jun Qi, Jiahao Xu, Fengan Zhang, Zhihao Liu and Qi Lu

Crystals 2025, 15(12), 1041; https://doi.org/10.3390/cryst15121041 - 5 Dec 2025

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Abstract

To address the issue of excessively rapid setting of alkali-activated slag (AAS), which significantly restricted its engineering application, this study systematically investigated the effects of incorporating fly ash (FA) and calcium hydroxide (CH) on fluidity, setting behavior, and compressive strength development. The reaction [...] Read more.

To address the issue of excessively rapid setting of alkali-activated slag (AAS), which significantly restricted its engineering application, this study systematically investigated the effects of incorporating fly ash (FA) and calcium hydroxide (CH) on fluidity, setting behavior, and compressive strength development. The reaction mechanisms and synergistic enhancement effects among GBFS, FA, and CH were analyzed using XRD and FT-IR techniques. Results demonstrated that the combined incorporation of FA and CH enabled effective and synergistic regulation of AAS. The calcium-supplying capability of CH counteracted the compressive strength loss induced by FA, thereby creating favorable conditions for FA to exert its effects in both delaying hydration and improving fluidity. With increasing FA content, the setting time was further extended, fluidity continued to improve, and the reduction in compressive strength was mitigated. The optimal comprehensive performance was achieved at a GBFS:FA:CH mass ratio of 6.5:3:0.5, yielding a 28 d compressive strength of 51.6 MPa, a fluidity of 188 mm, and initial and final setting times of 60 min and 81 min, respectively, representing improvements of 20% to 50% compared to the reference mixture. Microstructural analysis indicated that the addition of FA and CH supplemented calcium, silicon, and aluminum components in AAS, promoted the formation of silicate and aluminosilicate crystalline phases, enhanced the diversity of polycondensation products, and significantly increased the crosslinking degree of silicate and aluminate tetrahedra as well as the polymerization degree of the gel phase. These findings revealed the intrinsic mechanism behind the performance optimization of the composite system. Full article

(This article belongs to the Section Crystal Engineering)

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22 pages, 7385 KB

Open AccessArticle

Calcification Roasting-Microwave Acid Leaching of Vanadium from Vanadium-Bearing Steel Slag

by Le Wang, Minhao Zhang, Xueying Shao and Jinglong Liang

Crystals 2025, 15(12), 1040; https://doi.org/10.3390/cryst15121040 - 4 Dec 2025

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Abstract

Enhanced vanadium recovery from vanadium-bearing steel slag is essential in the sustainable use of metallurgical solid waste. This study uses microwave-assisted acid leaching on roasted clinker and systematically investigates it to enhance vanadium recovery; uses response surface methodology (RSM) to identify optimal parameters [...] Read more.

Enhanced vanadium recovery from vanadium-bearing steel slag is essential in the sustainable use of metallurgical solid waste. This study uses microwave-assisted acid leaching on roasted clinker and systematically investigates it to enhance vanadium recovery; uses response surface methodology (RSM) to identify optimal parameters for leaching; and the influences of sulfuric acid concentration, leaching time, liquid-to-solid ratio (L/S ratio), and leaching temperature on vanadium dissolution are evaluated. The optimal leaching parameters are identified as an L/S ratio of 10:1, 41% sulfuric acid concentration, 65 min leaching time, and 92 °C leaching temperature, under which the highest vanadium extraction rate is 84.58%. Kinetic studies revealed that the leaching behavior during the initial 30 min followed a shrinking core model with fixed particle size. The vanadium microwave-assisted acid leaching process exhibited the observed activation energy (E_a) of 37.30 kJ·mol⁻¹, following a kinetic order of 1.5392 relative to sulfuric acid concentration, implying that ion transport across the solid phase formed during the reaction determined the step that limits the reaction rate. The semi-empirical kinetic equation established in this study accurately describes the leaching behavior under different conditions. This research establishes a theoretical framework and technical reference for boosting vanadium recovery from steel slag, which uses microwave-assisted leaching technology. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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19 pages, 10122 KB

Open AccessArticle

Experimental Study on the Influence of Waste Stone Powder on the Properties of Alkali-Activated Slag/Metakaolin Cementitious Materials

by Tongkuai Wang, Haibo Wang and Chunmei Li

Crystals 2025, 15(12), 1039; https://doi.org/10.3390/cryst15121039 - 4 Dec 2025

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Abstract

Waste stone powder, as a solid waste resource, is characterized by its large volume, wide distribution, and low utilization rate. Its resource utilization is one of the important approaches to achieving closed-loop recycling development in the stone industry. This study aims to utilize [...] Read more.

Waste stone powder, as a solid waste resource, is characterized by its large volume, wide distribution, and low utilization rate. Its resource utilization is one of the important approaches to achieving closed-loop recycling development in the stone industry. This study aims to utilize waste stone powder as a mineral admixture in the preparation of alkali-activated cementitious materials, investigating the influence of parameters such as waste stone powder content, water-binder ratio, and Na₂O content on the mechanical properties, fluidity, setting time, and shrinkage behavior of the cementitious materials. The results indicate that both waste stone powder and the water-binder ratio can effectively improve the setting time and fluidity of the paste. However, higher waste stone powder content leads to more severe shrinkage, and a calculation model for material shrinkage was established. The optimal mechanical properties for alkali-activated slag samples were achieved with a Na₂O content of 8%, waste stone powder content of 16%, and a water-binder ratio of 0.45. For alkali-activated metakaolin samples, a waste stone powder content of 16% resulted in superior mechanical performance. Furthermore, the failure of all material samples was brittle, primarily exhibiting typical splitting failure. Based on damage theory, a calculation model for the load–displacement curve of the material was developed, providing reference and support for further research and application of this material Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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10 pages, 1674 KB

Open AccessArticle

Sintering of Aluminum Powder at Its 2/3 T_m via Sonication Assisted Mixing and Liquid Metal Sintering Method

by Jun Peng, Tao Wang and Shuai Zhang

Crystals 2025, 15(12), 1038; https://doi.org/10.3390/cryst15121038 - 4 Dec 2025

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Abstract

Powder metallurgy is an ideal technique for manufacturing metal matrix composites, owing to its capacity for near-net shape production and minimal material waste. However, a characteristic feature of the aluminum green compacts during the sintering process is the presence of natural oxide films [...] Read more.

Powder metallurgy is an ideal technique for manufacturing metal matrix composites, owing to its capacity for near-net shape production and minimal material waste. However, a characteristic feature of the aluminum green compacts during the sintering process is the presence of natural oxide films on the surfaces of aluminum powders, which limits the application of aluminum powder metallurgy technology. To address this, we propose a sonication-assisted mixing and liquid metal sintering strategy by which aluminum powder can be easily sintered at the temperature as low as 623 K, two-thirds of the melting point of aluminum. The present investigation demonstrates that the molten gallium enhances metallurgical bonding between the aluminum particles by acting as a “bridge” between adjacent aluminum particles and disrupting the oxide film inevitably existing on the outermost layer of aluminum powder. According to the performance analysis results, when the sintering temperature is as low as two-thirds of the melting point of aluminum, the compressive strength of the Al-5Ga sample increases by 62.5% compared with that of pure aluminum. This innovation will help powder metallurgy researchers to pursue sintering at low-temperature and has a sweeping impact on a wide range of powder metallurgy applications. Full article

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

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31 pages, 5231 KB

Open AccessReview

Recent Advances in MoS₂-Based Nanocomposites: Synthesis, Structural Features, and Electrochemical Applications

by Gaukhar Omashova, Aidyn Tussupzhanov, Sherzod Ramankulov, Karakoz Katpayeva, Dilnoza Baltabaeyeva, Nurken Mussakhan and Berik Kaldar

Crystals 2025, 15(12), 1037; https://doi.org/10.3390/cryst15121037 - 4 Dec 2025

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Abstract

This article presents a review of current research on the use of molybdenum disulfide (MoS₂) and its composites as promising materials for energy storage systems and functional coatings. Various MoS₂ morphologies, including nanoflowers, nanoplatelets, and nanorods, are considered, as well [...] Read more.

This article presents a review of current research on the use of molybdenum disulfide (MoS₂) and its composites as promising materials for energy storage systems and functional coatings. Various MoS₂ morphologies, including nanoflowers, nanoplatelets, and nanorods, are considered, as well as their effects on electrochemical properties and specific capacity. Particular attention is paid to strategies for modifying MoS₂ using carbon nanomaterials (graphene, carbon nanotubes, porous carbon) and conductive polymers, which improve electrical conductivity, structural stability, and durability of electrodes. The important role of chemical vapor deposition (CVD), which allows the formation of uniform coatings with high purity, controlled thickness, and improved performance characteristics, is noted. A comparative analysis of advances in the application of MoS₂ in sodium-ion batteries, supercapacitors, and microwave absorbers is provided. It has been shown that the synergy of MoS₂ with carbon and polymer components, as well as the use of advanced deposition technologies, including CVD, opens new prospects for the development of low-cost, stable, and highly efficient energy storage devices. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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20 pages, 17016 KB

Open AccessArticle

Surface Fatigue Behavior of Duplex Ceramic Composites Under High-Frequency Impact Loading with In Situ Accelerometric Monitoring

by Arash Kariminejad, Maksim Antonov, Piotr Klimczyk and Irina Hussainova

Crystals 2025, 15(12), 1036; https://doi.org/10.3390/cryst15121036 - 4 Dec 2025

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Abstract

In applications involving repeated high-frequency mechanical impacts, such as cutting, machining, or percussive operations, understanding the surface fatigue performance of advanced ceramics is critical. This study investigated the surface fatigue resistance of duplex oxide–carbide ceramic composites fabricated via spark plasma sintering, complementing prior [...] Read more.

In applications involving repeated high-frequency mechanical impacts, such as cutting, machining, or percussive operations, understanding the surface fatigue performance of advanced ceramics is critical. This study investigated the surface fatigue resistance of duplex oxide–carbide ceramic composites fabricated via spark plasma sintering, complementing prior work on their sliding wear performance. The composites, featuring a hybrid oxide–carbide structure, were tested using a cyclic impact setup with a 10 mm ZrO₂ ball activated with 12 hammers fixed to a rotary disc delivering 500,000 impacts per test. Surface degradation was quantified through three-dimensional profilometry to determine the net material loss and scar depth, while fatigue mechanisms were analyzed using scanning electron microscopy coupled with energy-dispersive spectroscopy. In situ monitoring was implemented using accelerometers to capture vibrational signatures during cycling loading, enabling real-time assessment of material response and damage evolution. The WC-containing composite (S2 AZW) exhibited the lowest surface fatigue wear loss (700 × 10³ µm³), whereas the ZrC-based composite (AZZ1) showed the highest (1535 × 10³ µm³). A distinct inverse correlation was observed between the average peak acceleration and fatigue wear loss. Frequency-domain analysis of accelerometric signals revealed progressive degradation patterns consistent with post-test surface damage, indicating that such signal features may serve as effective in situ indicators for tracking material fatigue in future applications. Full article

(This article belongs to the Special Issue Advanced Surface Engineering Materials: Characterization and Properties (2nd Edition))

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