Crystals

25 pages, 21734 KiB

Open AccessArticle

Formation Mechanism and Gemological Characteristics of “Yellow-Skinned” Nanhong Agate in Northeastern Yunnan, China: Evidence from Mineralogy and Geochemistry

by Qiuyun Song, Shitao Zhang, Wenzhou Pu, Liurunxuan Chen, Ruohan Zuo, Xianchao Chen, Dai Zhang and Wenlian Liu

Crystals 2025, 15(5), 488; https://doi.org/10.3390/cryst15050488 - 21 May 2025

Viewed by 21

Abstract

The “yellow-skinned” Nanhong agate represents a unique variety of Nanhong agate found in northeastern Yunnan, China, and it is highly valued for its distinctive yellow exterior and clear red–yellow interface. Owing to the limited research on this variety, the present study provides the [...] Read more.

The “yellow-skinned” Nanhong agate represents a unique variety of Nanhong agate found in northeastern Yunnan, China, and it is highly valued for its distinctive yellow exterior and clear red–yellow interface. Owing to the limited research on this variety, the present study provides the first comprehensive analysis. Field surveys and various laboratory techniques—including polarizing microscopy, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectrometry, ultraviolet–visible (UV-VIS) absorption spectrometry, Raman spectroscopy, micro X-ray diffraction (µ-XRD) with Rietveld refinement, electron microprobe analysis (EPMA), and laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS)—were utilized to investigate its gemological, microtextural, spectroscopic, and geochemical characteristics. Field surveys identified the occurrence states of the “yellow-skinned” Nanhong agate. The laboratory results indicate that the agate primarily consists of α-quartz, with minor amounts of moganite, goethite, and hematite. The coloring mechanism observed in this study is consistent with the findings of previous studies: the external yellow coloration is due to goethite, while the internal red hue is attributed to hematite. Its unique pseudo-granular silica (Type III) structure provides a foundational basis for the later formation of the “yellow-skinned” agate variety, and geochemical data reveal the distribution patterns of elements. Based on geological surveys and experimental data, the formation of the “yellow-skinned” Nanhong agate in northeastern Yunnan can be divided into two stages: first, hydrothermal fluids filled the vesicles in the Permian Emeishan Basalt Formation (P₂β), leading to the formation of primary Nanhong agate. Subsequently, the Type III primary agate underwent weathering, erosion, transport, and deposition in the red–brown sandy mudstone of the Lower Triassic Feixianguan Formation (T₁f). The sedimentary environment in the second stage facilitated the conversion of outer hematite into goethite, resulting in the distinct “yellow-skinned” appearance with a clear red–yellow boundary. Based on the occurrence and stratigraphic relations, this study constrains the formation age of the “yellow-skinned” Nanhong agate to approximately 261.6 Ma. Full article

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

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11 pages, 11226 KiB

Open AccessArticle

Transformation Mechanism of Undercooled Austenite and Deformation Behavior of a 1.2 GPa High-Strength Medium Mn Steel

by Ying Dong, Jiachen Xu, Lingming Meng, Qinghao Miao, Haobo Cui, Jiaxin Chen, Yu Du, Tao Liu, Qingdong Feng and Chengjun Zhu

Crystals 2025, 15(5), 487; https://doi.org/10.3390/cryst15050487 - 21 May 2025

Viewed by 51

Abstract

In this study, the phase transformation mechanism during the decomposition of undercooled austenite and its effect on the deformation behavior of a high-strength medium Mn steel were studied. The results indicate that the austenite formation during heating (α → γ) is a relatively [...] Read more.

In this study, the phase transformation mechanism during the decomposition of undercooled austenite and its effect on the deformation behavior of a high-strength medium Mn steel were studied. The results indicate that the austenite formation during heating (α → γ) is a relatively fast reaction. However, the transformation of undercooled prior austenite above the martensite start (M_s) temperature (γ → α) is difficult due to its high thermal stability. Only martensite transformation occurred during the final air-cooling stage following a 120-h isothermal treatment at 360 °C (slightly above M_s). The growth of martensite laths was limited by the boundaries of prior austenite grains and martensite packets. High-strength tensile properties were achieved, with a yield strength of 955 MPa, ultimate tensile strength of 1228 MPa, and total elongation of 11.6%. These properties result from the synergistic hardening effects of grain refinement, high-density lattice distortion, and an increased boundary length per unit area. The composition design with medium Mn content increased the processing window for high-strength martensite transformation, providing a theoretical basis for an energy-saving approach that depends on the decomposition transformation of undercooled austenite. Full article

(This article belongs to the Special Issue Advances in High Performance Metal Materials: Preparation, Properties, and Applications)

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13 pages, 3900 KiB

Open AccessArticle

Growth and Characterization of High Doping Concentration (2.1 at%) Ytterbium (Yb) Doped Lithium Niobate (LiNbO₃) Crystal: An Electrically Tunable Lasing Medium

by Kaicheng Wu, Mohammad Ahsanul Kabir, Kai-ting Chou and Shizhuo Yin

Crystals 2025, 15(5), 486; https://doi.org/10.3390/cryst15050486 - 21 May 2025

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Abstract

In this paper, we report on the growth and characterization of high doping concentration (2.1 at%) ytterbium (Yb) doped lithium niobate (Yb:LiNbO₃) crystal. By using a slightly modified Czochralski method, we have successfully grown a usable size (2 mm × 2 [...] Read more.

In this paper, we report on the growth and characterization of high doping concentration (2.1 at%) ytterbium (Yb) doped lithium niobate (Yb:LiNbO₃) crystal. By using a slightly modified Czochralski method, we have successfully grown a usable size (2 mm × 2 mm × 30 mm) Yb:LiNbO₃ single crystal. We also conducted the energy-dispersive X-ray spectroscopy (EDS) and the X-ray diffraction (XRD) analyses, which experimentally confirm that the grown crystal is a Yb:LiNbO₃ single crystal. We also measured the absorption and emission spectra of the grown crystal. It was found out that there is a near-flat broad emission within a spectral range of 1004–1030 nm when excited at 980 nm for this high doping concentration Yb:LiNbO₃ crystal. Such a near-flat broad emission can be very useful for realizing high slope efficiency ultrafast (femtosecond) lasing in the Yb:LiNbO₃ crystal due to the low quantum defect of the Yb:LiNbO₃ crystal. We also investigated the electro-optic effect of the Yb:LiNbO₃. The experimental result confirms that the electro-optic (EO) effect of a highly doped (2.1 at%) lithium niobate crystal is close to the EO value of the pure lithium niobate. Thus, the highly doped Yb:LiNbO₃ crystal can still be an effective electrically tunable lasing medium. It can enable electrically tunable, high slope efficiency femtosecond lasing due to the combined features, including (1) a near flat broad emission spectrum at the spectral range of 1004–1030 nm, (2) a non-compromised electro-optic effect at high doping concentration Yb:LiNbO₃ crystal, and (3) a low quantum defect. Full article

(This article belongs to the Special Issue Rare Earths-Doped Materials (3rd Edition))

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11 pages, 14805 KiB

Open AccessArticle

Dilute Paramagnetism and Non-Trivial Topology in Quasicrystal Approximant Fe₄Al₁₃

by Keenan E. Avers, Jarryd A. Horn, Ram Kumar, Shanta R. Saha, Peter Zavalij, Yuanfeng Xu, Bogdan Andrei Bernevig and Johnpierre Paglione

Crystals 2025, 15(5), 485; https://doi.org/10.3390/cryst15050485 - 21 May 2025

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Abstract

A very fundamental property of both weakly and strongly interacting materials is the nature of their magnetic response. In this work, we detail the growth of crystals of the quasicrystal approximant Fe₄Al₁₃ with an Al flux solvent method. We characterize [...] Read more.

A very fundamental property of both weakly and strongly interacting materials is the nature of their magnetic response. In this work, we detail the growth of crystals of the quasicrystal approximant Fe₄Al₁₃ with an Al flux solvent method. We characterize our samples using electrical transport and heat capacity, yielding results consistent with a simple non-magnetic metal. However, magnetization measurements portray an extremely unusual response for a dilute paramagnet and do not exhibit the characteristic Curie behavior expected for a weakly interacting material at high temperature. Electronic structure calculations confirm metallic behavior but also indicate that each isolated band near the Fermi energy hosts non-trivial topologies, including strong, weak, and nodal components, with resultant topological surface states distinguishable from bulk states on the (001) surface. With half-filled flat bands apparent in the calculation, but an absence of long-range magnetic order, the unusual quasi-paramagnetic response suggests the dilute paramagnetic behavior in this quasicrystal approximant is surprising and may serve as a test of the fundamental assumptions that are taken for granted for the magnetic response of weakly interacting systems. Full article

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

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16 pages, 3351 KiB

Open AccessArticle

Prediction of Dendrite Growth Velocity in Undercooled Binary Alloys Based on Transfer Learning and Molecular Dynamics Simulation

by Jia Wei, Mingyu Zhang, Shuai Li and Shu Li

Crystals 2025, 15(5), 484; https://doi.org/10.3390/cryst15050484 - 21 May 2025

Viewed by 8

Abstract

The growth velocity of the crystal–melt interface during solidification is one of the important parameters that determine the crystal growth morphology. However, both experimental investigations and theoretical calculations are time-consuming and labor-intensive. Moreover, machine learning (ML)-based methods are severely limited by the limited [...] Read more.

The growth velocity of the crystal–melt interface during solidification is one of the important parameters that determine the crystal growth morphology. However, both experimental investigations and theoretical calculations are time-consuming and labor-intensive. Moreover, machine learning (ML)-based methods are severely limited by the limited amount of available experimental data. In this work, the crystal–melt interface velocity of four alloy systems under different values of undercooling was calculated by molecular dynamics simulation. The results showed a similar trend to the experimental data. A framework including molecular dynamics (MD) calculation and a transfer learning (TL) model was proposed to predict the interface velocity of binary alloys during free solidification. In order to verify the effectiveness of the model, eight ML models were constructed based on pure experimental data for model comparison. The prediction ability of the different models was assessed from two perspectives: interpolation and extrapolation. The results show that, regardless of whether it is interpolation or extrapolation, the TL model driven by both physical information and experimental data is superior to ML models driven solely by experimental data. The interpretability analysis method reveals the specific role of feature values in the interface velocity prediction of binary alloys. Full article

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

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17 pages, 3829 KiB

Open AccessArticle

Innovative Dual-Functional Photocatalyst Design for Precision Water Remediation

by Yike Li and Xian Liu

Crystals 2025, 15(5), 483; https://doi.org/10.3390/cryst15050483 - 21 May 2025

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Abstract

This study pioneers the development of a synergistic Ag-doped molecularly imprinted TiO₂ photocatalyst (MIP-Ag-TiO₂) through a multi-strategy engineering approach, integrating molecular imprinting technology with plasmonic metal modification via a precisely optimized sol–gel protocol. Breaking from conventional non-selective photocatalysts, our material [...] Read more.

This study pioneers the development of a synergistic Ag-doped molecularly imprinted TiO₂ photocatalyst (MIP-Ag-TiO₂) through a multi-strategy engineering approach, integrating molecular imprinting technology with plasmonic metal modification via a precisely optimized sol–gel protocol. Breaking from conventional non-selective photocatalysts, our material features an engineered surface architecture that combines selective molecular recognition sites with enhanced charge separation capabilities, specifically tailored for the targeted degradation of recalcitrant salicylic acid (SA) contaminants. Advanced characterization (XRD, EPR, FT-IR, TEM-EDS) reveals unprecedented structure–activity relationships, demonstrating how template molecule ratios (Ti:SA = 5:1) and calcination parameters (550 °C) collaboratively optimize both adsorption selectivity and quantum efficiency. The optimized MIP-Ag-TiO₂ achieves breakthrough performance metrics: 98.6% SA degradation efficiency at 1% Ag doping, coupled with a record selectivity coefficient R = 7.128. Mechanistic studies employing radical trapping experiments identify a dual •OH/O_2⁻-mediated degradation pathway enabled by the Ag-TiO₂ Schottky junction. This work establishes a paradigm-shifting “capture-and-destroy” photocatalytic system that simultaneously addresses the critical challenges of selectivity and quantum yield limitations in advanced oxidation processes, positioning molecularly imprinted plasmonic photocatalysts as next-generation smart materials for precision water purification. Full article

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

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14 pages, 5702 KiB

Open AccessArticle

Co_0.85Bi_0.15Fe_1.9X_0.1O₄ (X = Ce⁴⁺, Sm³⁺, Ho³⁺, and Er³⁺) Nanoparticles with Selective Anticancer Activity: A Structural and Morphological Approach

by Liza Saher, Adel Benali, Saoussen Haddad, Essebti Dhahri, Manuel P. F. Graça, Benilde F. O. Costa, Luisa A. Helguero and Artur M. S. Silva

Crystals 2025, 15(5), 482; https://doi.org/10.3390/cryst15050482 - 20 May 2025

Viewed by 91

Abstract

In this work, we synthesized the Co_0.85Bi_0.15Fe_1.9X_0.1O₄ (X = Ce³⁺, Sm³⁺, Ho³⁺, and Er³⁺) nanoparticles via the auto-combustion method. The cell viability against two breast cancer [...] Read more.

In this work, we synthesized the Co_0.85Bi_0.15Fe_1.9X_0.1O₄ (X = Ce³⁺, Sm³⁺, Ho³⁺, and Er³⁺) nanoparticles via the auto-combustion method. The cell viability against two breast cancer cells (MDA-MB-231 and T-47D cells) and the PC3 prostate cancer cells were carefully analyzed and correlated with the structural parameters and particle size values as well as the chemical composition. The produced compounds’ morphological and structural characteristics were performed using scanning transmission microscopy (TEM) and X-ray Diffraction (XRD). For all compounds, the analyses of the XRD experimental data revealed a structurally reversed cubic spinel with space group Fd-3m. All of the compounds had crystallites smaller than 45 nm which concorded well with the particle size values deduced from TEM images. Co_0.85Bi_0.15Fe_1.9Ho_0.1O₄ nanoparticles induced a high mortality of breast and prostate cancer cells (MDA-MB-231, T-47D, and PC3) while the Co_0.85Bi_0.15Fe_1.9Sm_0.1O₄ compound (higher particle size) reduced almost 35% of MDA-MB-231 cancer cells. With very low cytotoxicity against normal human cells, the Co_0.85Bi_0.15Fe_1.9Ho_0.1O₄ nanoparticles play a significant role in the elimination of cancer cells. Full article

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

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13 pages, 3088 KiB

Open AccessArticle

Damage Simulation Study of Composite-to-Metal Interference-Fit with Multiple Structural Parameters

by Shan Jiang, Xiao Guo, Rui Zhao, Dongxu Zhang and Min Wan

Crystals 2025, 15(5), 481; https://doi.org/10.3390/cryst15050481 - 20 May 2025

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Abstract

Composite-to-metal interference-fit is widely used in the aerospace field, where the problem of the damage and failure of composite materials is particularly critical. A numerical study was conducted on the damage and failure of carbon fiber composite sleeves with multiple structural parameters during [...] Read more.

Composite-to-metal interference-fit is widely used in the aerospace field, where the problem of the damage and failure of composite materials is particularly critical. A numerical study was conducted on the damage and failure of carbon fiber composite sleeves with multiple structural parameters during interference-fit assembly. ABAQUS/Explicit simulation of interference-fit was performed with the three-dimensional finite element method, and the VUMAT subroutine with three-dimensional Hashin damage was utilized to investigate the initiation and evolution of composite component damage. The effects of different relative wall thicknesses and layup sequences on the selection of maximum interference were analyzed. The results reveal that the stress distribution on the inner surface of the sleeve is more uniform with the condition of radial layup. Radial layup enables 0.2% interference at 25% wall thickness, a 100% increase over axial layup. This study contributes to addressing long-standing issues in the aerospace field, such as connection failure and insufficient fatigue life. It is of great significance for improving structural performance, reducing costs, and promoting technological innovation. Full article

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

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10 pages, 2233 KiB

Open AccessArticle

Determination of the ²⁰⁷Pb Chemical Shift Tensor in Crocoite, PbCrO₄, Using Single-Crystal NMR Spectroscopy

by Sebastian Kläger, Otto E. O. Zeman and Thomas Bräuniger

Crystals 2025, 15(5), 480; https://doi.org/10.3390/cryst15050480 - 19 May 2025

Viewed by 106

Abstract

The full chemical shift tensor of ²⁰⁷Pb (spin

I = 1 / 2

) in the natural mineral crocoite, PbCrO₄, has been determined using single-crystal NMR spectroscopy at room temperature. The eigenvalues of the tensor in its principal axes system [...] Read more.

The full chemical shift tensor of ²⁰⁷Pb (spin

I = 1 / 2

) in the natural mineral crocoite, PbCrO₄, has been determined using single-crystal NMR spectroscopy at room temperature. The eigenvalues of the tensor in its principal axes system are

δ_{11} = - 2720 \pm 2

ppm,

δ_{22} = - 2319 \pm 4

ppm, and

δ_{33} = - 1830 \pm 5

ppm, resulting in an isotropic chemical shift of

δ_{iso} = - 2289 \pm 2

ppm. Additionally, these values were verified using a Herzfeld–Berger analysis of a polycrystalline sample under magic-angle spinning (MAS) conditions. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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16 pages, 5110 KiB

Open AccessArticle

Effects of Nitrogen Partial Pressure on the Microstructure and Mechanical Properties of High-Entropy Ti(C,N)-Based Gradient Cermets

by Yunhao Zhang, Houan Zhang, Dongxu Qiao, Xin Tao, Peng Xia and Siyong Gu

Crystals 2025, 15(5), 479; https://doi.org/10.3390/cryst15050479 - 19 May 2025

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Abstract

Titanium carbonitride (Ti(C,N))-based ceramics are widely utilized in mechanical machining, aerospace, and electronics, particularly in cutting tools and wear-resistant components. Two single-phase solid solution powders, non-high-entropy (Ti_0.83,W_0.07,Mo_0.04,Nb_0.03,Ta_0.04)(C_0.7,N_0.3) and high-entropy [...] Read more.

Titanium carbonitride (Ti(C,N))-based ceramics are widely utilized in mechanical machining, aerospace, and electronics, particularly in cutting tools and wear-resistant components. Two single-phase solid solution powders, non-high-entropy (Ti_0.83,W_0.07,Mo_0.04,Nb_0.03,Ta_0.04)(C_0.7,N_0.3) and high-entropy (Ti_0.6,W_0.1,Mo_0.1,Nb_0.1,Ta_0.1)(C_0.78,N_0.22), were synthesized via the carbothermal reduction–nitridation (CRN) method. Gradient-structured non-high-entropy (C-TiCN) and high-entropy (HE-TiCN) cermets were fabricated at 1450 °C by tailoring the nitrogen partial pressure in the range of 1–8 kPa. The effect of nitrogen partial pressure on the microstructure and mechanical properties of both materials was thoroughly analyzed. Both materials exhibited a three-layer gradient structure comprising a hard-phase-enriched surface layer, a binder-rich subsurface layer, and a chemically uniform core. Optimal performance was achieved at 4 kPa nitrogen partial pressure, at which both HE-TiCN and C-TiCN exhibited a desirable combination of surface hardness and fracture toughness. Compared with C-TiCN, HE-TiCN showed improvements in surface hardness and fracture toughness at subsurface and core regions (40 µm from the surface) by 4.9%, 11.2%, and 12.0%, respectively. The enhanced surface hardness of HE-TiCN is attributed to the significant lattice distortion and the synergistic effects associated with its high-entropy configuration. The improved toughness of the binder-rich layer is primarily ascribed to mechanisms such as crack deflection, crack branching, and the formation of tear ridges. These findings offer a promising strategy for developing gradient Ti(C,N)-based cermets with enhanced mechanical performance. Full article

(This article belongs to the Special Issue Structure and Properties of Ceramic Materials)

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19 pages, 7635 KiB

Open AccessArticle

Hydrogen Reduction of Tellurium Oxide in a Rotary Kiln, Initial Approaches for a Sustainable Process

by Hanwen Chung, Semiramis Friedrich, Mengqi Qu and Bernd Friedrich

Crystals 2025, 15(5), 478; https://doi.org/10.3390/cryst15050478 - 18 May 2025

Viewed by 139

Abstract

In the recycling of semiconductor materials like Bi₂Te₃ or CdTe, TeO₂ may form as a by-product that can be directly reduced to recover metallic Te. The hydrogen reduction of TeO₂ offers an eco-friendly alternative to conventional carbothermic reduction [...] Read more.

In the recycling of semiconductor materials like Bi₂Te₃ or CdTe, TeO₂ may form as a by-product that can be directly reduced to recover metallic Te. The hydrogen reduction of TeO₂ offers an eco-friendly alternative to conventional carbothermic reduction by avoiding CO by-products. This study investigates the reduction of 99.99 wt.% purity level TeO₂ using hydrogen in an oscillating kiln furnace (200–800 °C, 2–7 h), with phase composition and microstructure analysed via XRD and SEM. Results demonstrate conversions of up to 89% (solid–gas) and 100% (liquid–gas), revealing that kinetics dominate over thermodynamics in controlling reaction progress. The work proposes a reaction mechanism based on morphological evolution observed in SEM images, suggesting that further parameter optimisation could enhance scalability. As the first lab-scale demonstration of hydrogen-assisted TeO₂ reduction, this study establishes a preliminary process window (temperature/time) and underscores the potential for industrial adoption. Future work should verify the proposed mechanism and refine operational parameters to maximize efficiency. Full article

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

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16 pages, 4366 KiB

Open AccessArticle

Numerical Simulation of the Effect of APCVD Reactor Tilted Ceiling Height on Silicon Epitaxial Layer Thickness Uniformity

by Ba-Phuoc Le, Jyh-Chen Chen, Chieh Hu, Wei-Jie Lin, Chun-Chin Tu and Liang-Chin Chen

Crystals 2025, 15(5), 477; https://doi.org/10.3390/cryst15050477 - 18 May 2025

Viewed by 126

Abstract

As the linewidth of semiconductor nanostructures continues to decrease, the criteria for acceptable surface homogeneity of silicon (Si) epi-films are becoming increasingly stringent. To address this challenge, the effect of different tilted ceiling heights on the Si epi thickness homogeneity in an atmospheric [...] Read more.

As the linewidth of semiconductor nanostructures continues to decrease, the criteria for acceptable surface homogeneity of silicon (Si) epi-films are becoming increasingly stringent. To address this challenge, the effect of different tilted ceiling heights on the Si epi thickness homogeneity in an atmospheric pressure chemical vapor deposition (APCVD) reactor is investigated numerically. In this study, the deposition temperature on the wafer is controlled at 1373 K. When a tilted ceiling with decreasing height along the streamwise direction is used, the average gas mixture velocity increases with the streamwise direction, which can reduce the impact of flow distortion caused by the rotation of the susceptor. At the same time, the growth of the reaction boundary layer on the wafer is suppressed, which helps with the diffusion of trichlorosilane (TCS) on the wafer surface. This makes the drop in the TCS concentration along the streamwise direction more linear, thereby improving the linearity of the growth rate on the wafer surface along the streamwise direction. Therefore, the present results for a reactor without an inlet plate show that the thickness homogeneity across the entire surface of the wafer after a complete susceptor rotation can be significantly improved by linearly reducing the ceiling height in the streamwise direction. A further increase in the inclination of the inclined ceiling leads to a further improvement in the deposition homogeneity. However, the growth rate values at the same position perpendicular to the streamwise direction are inconsistent, which is not conducive to deposition homogeneity. This shortcoming can be improved upon by using a four-inlet plate reactor with an inclined top plate and by properly selecting the position of each partition and the inlet gas mixture velocity of each inlet channel, thereby greatly increasing the deposition homogeneity of the Si epi-layer. For the cases considered in this study, the deposition thickness non-homogeneity across the wafer surface decreased from 38% to 3%. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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13 pages, 3206 KiB

Open AccessArticle

Influence of Yttria Nanoclusters on the Void Nucleation in BCC Iron During Multi-Axial Tensile Deformation: A Molecular Dynamics Simulation

by Zhenyu Wei, Yongjie Sun, Yeshang Hu, Lei Peng, Jingyi Shi, Yifan Shi, Shangming Chen and Yiyi Ma

Crystals 2025, 15(5), 476; https://doi.org/10.3390/cryst15050476 - 18 May 2025

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Abstract

Oxide dispersion-strengthened (ODS) steels are among the most promising candidate structural materials for fusion and Generation-IV (Gen-IV) fission reactors, but the ductility of ODS steels is inferior to its strength properties. Therefore, we investigate void nucleation, considered as the first step of ductile [...] Read more.

Oxide dispersion-strengthened (ODS) steels are among the most promising candidate structural materials for fusion and Generation-IV (Gen-IV) fission reactors, but the ductility of ODS steels is inferior to its strength properties. Therefore, we investigate void nucleation, considered as the first step of ductile damage in metal, using molecular dynamics simulations. Given that the materials are subjected to extremely complex stress states within the reactor, we present the void nucleation process of 1–4 nm Y₂O₃ nanoclusters in bcc iron during uniaxial, biaxial, and triaxial tensile deformation. We find that the void nucleation process is divided into two stages depending on whether the dislocations are emitted. Void nucleation occurs at smaller strain in biaxial and triaxial tensile deformation in comparation to uniaxial tensile deformation. Increasing the size of clusters results in a smaller strain for void nucleation. The influence of 1 nm clusters on the process of void nucleation is slight, and the void nucleation process of 1 nm cluster cases is similar to that of pure iron. In addition, void nucleation is affected by both stress and strain concentration around the clusters, and the voids grow first in the areas of high stress triaxiality. Full article

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

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15 pages, 6028 KiB

Open AccessArticle

Crystalline Li-Ta-Oxychlorides with Lithium Superionic Conduction

by Hao-Tian Bao, Bo-Qun Cao and Gang-Qin Shao

Crystals 2025, 15(5), 475; https://doi.org/10.3390/cryst15050475 - 17 May 2025

Viewed by 146

Abstract

Nowadays, some amorphous and microcrystalline solid-state electrolytes (SSEs) with dual anions have attained high ionic conductivity and good compatibility with electrodes in all-solid-state lithium-ion batteries (ASSLIBs). In this work, crystalline SSEs of series A (Li_1+xTaO_1+xCl_4−x [...] Read more.

Nowadays, some amorphous and microcrystalline solid-state electrolytes (SSEs) with dual anions have attained high ionic conductivity and good compatibility with electrodes in all-solid-state lithium-ion batteries (ASSLIBs). In this work, crystalline SSEs of series A (Li_1+xTaO_1+xCl_4−x, −0.70 ≤ x ≤ 0.50) and B (LiTaO_2+yCl_2−2y, −1.22 ≤ y ≤ 0), having great application potential well over ambient temperatures, were prepared at 260–460 °C for 2–10 h using Li₂O, TaCl₅, and LiTaO₃ as the raw materials. The three-phase coexisting samples attained high σ values ranging from 5.20 to 7.35 mS cm⁻¹, which are among the reported high values of amorphous co-essential SSEs and other alloplasmatic crystalline ones. It is attributed to the synergistic effect of the polyanion trans-[O₂Cl₄] and cis-[O₄Cl₂] octahedra framework. Full article

(This article belongs to the Special Issue Synthesis, Structure and Application of Metal Halides)

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28 pages, 7859 KiB

Open AccessArticle

Tailoring the Luminescence Properties of Strontium Aluminate Phosphors for Unique Smartphone Detectable Optical Tags

by Virginija Vitola, Milena Dile, Katrina Krizmane, Ernests Einbergs, Tinko Eftimov, Kristian Nikolov and Samia Fouzar

Crystals 2025, 15(5), 474; https://doi.org/10.3390/cryst15050474 - 17 May 2025

Viewed by 114

Abstract

In this work, a precursor-driven tailoring of strontium aluminate phosphors doped with Eu²⁺ and Dy³⁺ to generate unique, batch-specific luminescent signatures suitable for smartphone-detectable anti-counterfeiting tags was developed. A microwave-assisted hydrothermal synthesis approach was employed to explore the impact of a [...] Read more.

In this work, a precursor-driven tailoring of strontium aluminate phosphors doped with Eu²⁺ and Dy³⁺ to generate unique, batch-specific luminescent signatures suitable for smartphone-detectable anti-counterfeiting tags was developed. A microwave-assisted hydrothermal synthesis approach was employed to explore the impact of a wide range of alkaline hydroxide and carbonate precursors on the structure of strontium aluminate. The resulting materials exhibited distinct differences in crystalline phase composition, morphology, and trap depth distribution. A smartphone-based detection system was developed, enabling rapid identification of spectral fingerprints. This study demonstrates a viable strategy for embedding unique luminescent identifiers, offering a scalable solution for robust, low-cost anti-counterfeiting applications in both the spectral and the time domain. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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13 pages, 5475 KiB

Open AccessArticle

Dimensional Management of Fabricated Silver Nanoparticles via Concurrent Chemical Reduction with Long-Pulsed Laser Fragmentation in Origanum majorana Extract

by Entesar A. Ganash and Reem M. Altuwirqi

Crystals 2025, 15(5), 473; https://doi.org/10.3390/cryst15050473 - 16 May 2025

Viewed by 69

Abstract

A straightforward and economical engraving diode laser with a 455

\pm

5

nm visible wavelength was employed for the first time in a pulsed laser fragmentation in liquid (PLFL) technique coupled simultaneously with a chemical reduction method to synthesize silver nanoparticles (AgNPs) in [...] Read more.

A straightforward and economical engraving diode laser with a 455

\pm

5

nm visible wavelength was employed for the first time in a pulsed laser fragmentation in liquid (PLFL) technique coupled simultaneously with a chemical reduction method to synthesize silver nanoparticles (AgNPs) in an Origanum majorana extract liquid, as a natural reduction agent. The chemical reduction correlated with the PLFL method to control the NP size by examining the effect of irradiation times. The AgNPs were characterized by X-Ray diffraction (XRD), UV–vis spectrophotometry, dynamic light scattering (DLS), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The lattice diffraction Bragg’s planes (111), (200), (220), (311), and (222) were found by XRD. The AgNPs had a surface plasmon resonance (SPR) peak at around 432–409 nm. The position of this SPR peak moves toward shorter wavelengths, by around 23 nm, with increased laser irradiation. When exposure times were increased, a drop in Ag NP size was revealed, from 22 nm when only a chemical reduction approach was used to 12 nm when the PLFL technique was associated. The DLS and TEM confirmed the UV–vis results. Such consideration suggests that combining the chemical reduction and PLFL methods could enable the tuning of the Ag NP size to be tailored for specific applications. This work could open the field for synthesizing NPs and controlling their size using an easy and handy engraving laser. Full article

(This article belongs to the Special Issue Novel Nano-Materials: Material Characterization and Structural Analysis)

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10 pages, 4485 KiB

Open AccessArticle

Surface Morphology of 6-Inch SiC Single Crystals in Solution Growth on Si-Face, C-Face and (

10 \bar{1} \bar{2}

) Plane

by Gangqiang Liang, Jiayi Kuang, Yilin Su and Yuan Liu

Crystals 2025, 15(5), 472; https://doi.org/10.3390/cryst15050472 - 16 May 2025

Viewed by 81

Abstract

For solution growth of 6-inch 4H-SiC bulk crystals, the surface step morphology of the crystals grown on Si-face, C-face and (

10 \bar{1} \bar{2}

) plane was systematically characterized by laser confocal microscopy. The 2D-nucleation and step-bunching were likely to occur [...] Read more.

For solution growth of 6-inch 4H-SiC bulk crystals, the surface step morphology of the crystals grown on Si-face, C-face and (

10 \bar{1} \bar{2}

) plane was systematically characterized by laser confocal microscopy. The 2D-nucleation and step-bunching were likely to occur during the 30 h growth on Si-face, leading to a rough surface with a macro-step height over 60 μm. By contrast, the step heights were maintained at 0.1–1 μm during 60 h growth on C-face, exhibiting good morphological stability for long-term growth. Moreover, the SiC crystal grown on the (

10 \bar{1} \bar{2}

) plane illustrated its excellence in producing fine steps, which is attributed to the smaller interfacial energy between the solution and (

10 \bar{1} \bar{2}

) substrates, suggesting that it offers a better approach to growing SiC single bulk crystals. Full article

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

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15 pages, 3811 KiB

Open AccessArticle

Mechanistic Decoupling of Giant Electrostrain and Piezoelectric Coefficients at the Morphotropic Phase Boundary in PMN-30PT Single Crystals

by Ruqing Yan, Shuai Li, Jianting Li, Junjie Li, Yaodong Yang, Wei-Feng Rao and Yang Bai

Crystals 2025, 15(5), 471; https://doi.org/10.3390/cryst15050471 - 16 May 2025

Viewed by 62

Abstract

The morphotropic phase boundary (MPB) with multiphase coexistence serves as a critical region for piezoelectric materials, but the individual contributions of various microscopic mechanisms to the overall electromechanical response remains a challenge for further subdivision. Here, we systematically investigate the microscopic origins of [...] Read more.

The morphotropic phase boundary (MPB) with multiphase coexistence serves as a critical region for piezoelectric materials, but the individual contributions of various microscopic mechanisms to the overall electromechanical response remains a challenge for further subdivision. Here, we systematically investigate the microscopic origins of outstanding piezoelectricity in <001>-oriented Pb(Mg_1/3Nb_2/3)O₃-30PbTiO₃ (PMN-30PT) single crystals and quantitatively identify the dominant factors for giant electrostrain and ultrahigh piezoelectric coefficient. Large electrostrain arises predominantly from polarization rotation within the easily distorted monoclinic phase and the high-energy-barrier monoclinic-to-tetragonal phase transition, enabled by a synergistic interplay of broad electric field adaptability and high strain sensitivity. In contrast, the peak piezoelectric coefficient (d₃₃ > 2100 pC/N) is attributed to the low-energy-barrier rhombohedral-to-monoclinic phase transition, which facilitates polarization rotation. Furthermore, the critical yet distinct roles of monoclinic phase compared to piezoelectric and electrostrain have been confirmed. By the quantitative segmentation of various microscopic factors, this work provides fundamental insights into the design of high-performance piezoelectrics. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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20 pages, 4370 KiB

Open AccessArticle

Eco-Friendly Synthesis of ZnO Nanoparticles from Natural Agave, Chiku, and Soursop Extracts: A Sustainable Approach to Antibacterial Applications

by G. Mustafa Channa, Jackeline Iturbe-Ek, Alan O. Sustaita, Dulce V. Melo-Maximo, Atiya Bhatti, Juan Esparza-Sanchez, Diego E. Navarro-Lopez, Edgar R. Lopez-Mena, Angelica Lizeth Sanchez-Lopez and Luis Marcelo Lozano

Crystals 2025, 15(5), 470; https://doi.org/10.3390/cryst15050470 - 16 May 2025

Viewed by 140

Abstract

Traditional methods of synthesizing nanoparticles often rely on physical and chemical processes using synthetic hazardous chemicals. In contrast, the rise in green chemistry emphasizes using bioactive compounds from plants for the eco-friendly synthesis of nanostructures. These green synthesis techniques are increasingly recognized for [...] Read more.

Traditional methods of synthesizing nanoparticles often rely on physical and chemical processes using synthetic hazardous chemicals. In contrast, the rise in green chemistry emphasizes using bioactive compounds from plants for the eco-friendly synthesis of nanostructures. These green synthesis techniques are increasingly recognized for their simplicity, cost-effectiveness, and ability to yield non-toxic by-products, an approach that aligns with sustainable practices. In this research, a straightforward, cheap, environmentally friendly, and sustainable procedure was developed to fabricate Zinc oxide nanoparticles (ZnO-NPs) employing three different pulp extracts: Agave (Agave americana), Chiku (Manilkara zapota), and Soursop (Annona muricata) to serve in the synthesis as capping, reduction, or stabilization agent. Analytical characterization techniques confirmed the successful phytosynthesis of ZnO-NPs, evidenced by significant absorbance peaks of UV-Vis spectra at 362 nm, and the chemical composition of ZnO without noticeable traces of phytochemical residues by carrying out ATR-FTIR analysis. SEM, STEM microscopies, and XRD analysis verified that the ZnO nanoparticles possess spherical geometries and hexagonal crystal structures. The average size of these nanoparticles was around 15.94, 18.08, and 23.32 nm for Agave, Chiku, and Soursop extract-based synthesis, respectively. Additionally, the in vitro antibacterial activity of phytosynthetized ZnO-NPs was evaluated against E. coli and S. aureus, confirming effective bacterial growth inhibition and demonstrating their significant antimicrobial potential. Full article

(This article belongs to the Special Issue Metal Oxide-Based Nanomaterials: Advances in Synthesis, Characterization, and Applications)

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24 pages, 100135 KiB

Open AccessArticle

The Influence of Annealing Temperature on the Microstructure and Performance of Cold-Rolled High-Conductivity and High-Strength Steel

by Shuhai Ge, Xiaolong Zhao, Weilian Zhou, Xueming Xu, Xingchang Tang, Junqiang Ren, Jiahe Zhang and Yaoxian Yi

Crystals 2025, 15(5), 469; https://doi.org/10.3390/cryst15050469 - 16 May 2025

Viewed by 69

Abstract

Low-carbon micro-alloyed steel has become a wire material with great potential for further development due to its excellent comprehensive performance; however, there is still a lack of insight into the evolution of its electrical conductivity during annealing treatment after undergoing deformation. In this [...] Read more.

Low-carbon micro-alloyed steel has become a wire material with great potential for further development due to its excellent comprehensive performance; however, there is still a lack of insight into the evolution of its electrical conductivity during annealing treatment after undergoing deformation. In this present contribution, we systematically explored the intrinsic correlation between the microstructural characteristics (including grain size evolution, dislocation density change, etc.) and performance indexes of cold-rolled high-conductivity high-strength steels and their mechanisms, using the annealing temperature, a key process parameter, as a variable. Characterization methods were used to comprehensively investigate the variation rule of the electrical conductivity of low-carbon micro-alloyed steels containing Ti-Nb elements under different annealing temperatures, as well as their influencing factors. The results show that for the ultra-low-carbon steel (0.002% C), the dislocation density continuously decreases with the increasing annealing temperature. Both experimental steels underwent complete recrystallization at 600 °C, with grain growth increasing at higher temperatures (with ultra-low-carbon steel being finer than low-carbon steel (0.075% C)). Dislocation density in ultra-low-carbon steel decreased steadily, whereas low-carbon steel exhibited an initial decline followed by an increase due to carbon-rich precipitate pinning. The yield ratio decreased with the annealing temperature, with optimal performance being at 700 °C for ultra-low-carbon steel (lowest resistivity: 13.75 μΩ/cm) and 800 °C for low-carbon steel (best conductivity: 14.66 μΩ/cm). Yield strength in ultra-low-carbon steel was dominated by grain and precipitation strengthening, while low-carbon steel relied more on precipitation and solid solution strengthening. Resistivity analysis confirmed that controlled precipitate size enhances conductivity. Full article

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

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22 pages, 3817 KiB

Open AccessArticle

Machine Learning Unveils the Impacts of Key Elements and Their Interaction on the Ambient-Temperature Tensile Properties of Cast Titanium Aluminides Employing SHAP Analysis

by Shiqiu Liu and Li Liang

Crystals 2025, 15(5), 468; https://doi.org/10.3390/cryst15050468 - 16 May 2025

Viewed by 51

Abstract

This study facilitates the data-driven design of novel cast TiAl alloys by systematically investigating the critical elements and their interactions affecting room-temperature (RT) tensile properties by the machine learning method based on SHAP analysis. Comparative analysis of three algorithms within the training dataset [...] Read more.

This study facilitates the data-driven design of novel cast TiAl alloys by systematically investigating the critical elements and their interactions affecting room-temperature (RT) tensile properties by the machine learning method based on SHAP analysis. Comparative analysis of three algorithms within the training dataset proved the random forest regression (RFR) as the optimal modeling approach. To evaluate model performance and prevent overfitting, leave-one-out cross-validation (LOOCV) was simultaneously implemented during training. All the three well-trained models demonstrated robust predictive capabilities for ultimate tensile strength (UTS), elongation (EL), and yield strength (YS). Detailed investigation on both the magnitude and directionality of feature importance and interaction disclosed distinct elemental influences: B, C, and Nb predominantly improved UTS and YS, while Cr, Mn, and Al positively affected EL. The highly probable direction of feature interaction between two different elements on the RT tensile properties of cast TiAl alloys was basically revealed. Notably, Al–B interactions enhance UTS at Al < 45.5 at%; Cr–Mn synergistically improves EL when Cr > 1 at%; both Al–B and Al–C interactions boost YS within 44–46 at% Al. Despite a slight distinction in casting technology, this research established a qualitative relationship between the chemical elements and the RT tensile properties of TiAl alloys, providing design recommendations for cast TiAl alloys with excellent RT tensile properties. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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28 pages, 13778 KiB

Open AccessReview

Research Progress on the Application of Carbon-Based Materials in Electrocatalytic CO₂ Reduction Reaction

by Xinyuan Yang, Guifan Gong, Aoxiang Yin, Runyao Han, Jirong Yao, Zimeng Liu, Hui Ming and Mei Wu

Crystals 2025, 15(5), 467; https://doi.org/10.3390/cryst15050467 - 15 May 2025

Viewed by 119

Abstract

The conversion of CO₂ into high-value-added chemicals and fuels using electricity generated from renewable energy sources is one of the most promising methods to reduce the dependence of human society on fossil fuels and to alleviate environmental problems. The performance of catalysts [...] Read more.

The conversion of CO₂ into high-value-added chemicals and fuels using electricity generated from renewable energy sources is one of the most promising methods to reduce the dependence of human society on fossil fuels and to alleviate environmental problems. The performance of catalysts is one of the most important factors restricting the development of this technology, and in recent years, carbon materials have been the hot spot of research in the field of CO₂ electrocatalytic reduction catalysts. In this paper, the progress of the application of carbon materials in CO₂ electrocatalytic reduction reaction (ECR) is reviewed in detail. Three aspects of carbon materials directly as metal-free carbon material catalysts for CO₂ reduction, metal-centered coatings in metal catalysts, and support for metals, are comprehensively described, respectively, including the preparation strategy of catalysts, the mechanism of action and structural characteristics of catalysts, the distribution of products and the catalytic performance of catalysts. Finally, the problems and challenges faced by the field are summarized, and the outlook is presented in various areas, including catalyst preparation, performance enhancement, and deepening mechanism research. Full article

(This article belongs to the Special Issue Synthesis and Catalytic Performance of Transition Metal Catalysts)

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29 pages, 11372 KiB

Open AccessArticle

Biological Control of Ca-Carbonate Crystal Microstructure and Texture: Adapting Crystal Morphology, Orientation, and Arrangement to Biomaterial Function

by Anna Sancho Vaquer, Erika Griesshaber, Juan Diego Castro-Claros, Carmen Salas, Xiaofei Yin, Antonio G. Checa and Wolfgang W. Schmahl

Crystals 2025, 15(5), 466; https://doi.org/10.3390/cryst15050466 - 15 May 2025

Viewed by 125

Abstract

The mineralized cover of chiton (Polyplacophora) soft tissue consists of aragonite, developed as shell-plates, girdle-scales, and girdle-spicules. This study characterizes crystallographic aspects of the girdle-spicules of the species Ischnochiton rissoi, Rhyssoplax olivacea, Acanthopleura vaillantii, and Acanthopleura spinosa. Spicule crystal [...] Read more.

The mineralized cover of chiton (Polyplacophora) soft tissue consists of aragonite, developed as shell-plates, girdle-scales, and girdle-spicules. This study characterizes crystallographic aspects of the girdle-spicules of the species Ischnochiton rissoi, Rhyssoplax olivacea, Acanthopleura vaillantii, and Acanthopleura spinosa. Spicule crystal arrangements and texture variations are described. Different misorientations between the spicule crystals are shown and are discussed with respect to the physical properties of the biomaterial. Characterization was performed with electron backscattered diffraction (EBSD), as well as with laser confocal and Field emission scanning electron microscopy (FE-SEM) imaging. All investigated species had porous spicules and distinct structural characteristics. Spicule crystal co-orientation strength was strongly increased for R. olivacea and I. rissoi, and it was almost random for A. vaillantii. R. olivacea, I. rissoi. A. spinosa spicule crystal texture was axial, whereas A. vaillantii spicule crystals were almost untextured. For all species investigated, spicule aragonite was twinned, as demonstrated with the strong 63°/64° peak in the misorientation angle distribution diagram, indicating a {110}-twin relationship. R. olivacea and I. rissoi spicules consisted of few twinned crystals and twin boundaries; A. vaillantii and A. spinosa spicules showed an abundance of twinned crystals and twin boundaries. We observed a difference in spicule dimension, morphology, arrangement on the girdle, and crystal organization for the investigated species, but always the generation of twinned aragonite. Full article

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

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16 pages, 4136 KiB

Open AccessArticle

Synthesis and Characterization of MgO-ZrO₂ Heterostructure: Optical, Mechanical and Electrical Properties

by Tabasum Huma, Nadimullah Hakimi, Muhammad Anwar ul haq, Tanzeel Huma, Lei Xu and Xinkun Zhu

Crystals 2025, 15(5), 465; https://doi.org/10.3390/cryst15050465 - 15 May 2025

Viewed by 138

Abstract

The synthesis and characterization of MgO-ZrO₂ heterostructures are examined in this work. To promote the creation of nanowires, the Si substrate is first covered with a catalyst layer of various Au thicknesses. Sputtering is used to achieve this deposition. After that, chemical [...] Read more.

The synthesis and characterization of MgO-ZrO₂ heterostructures are examined in this work. To promote the creation of nanowires, the Si substrate is first covered with a catalyst layer of various Au thicknesses. Sputtering is used to achieve this deposition. After that, chemical vapor deposition (CVD) with a Au catalyst layer is used to create MgO nanowire arrays on the silicon substrate. Second, MgO/ZrO₂ Core–shell Nanowire Arrays are created by applying ZrO₂ layers to the surface of MgO nanowires of different diameters using chemical vapor deposition (CVD) procedures. The presence of both magnesium oxide (MgO) and zirconium dioxide (ZrO₂) in their oxidized forms was shown by the detailed characterization of the MgO-ZrO₂ core–shell nanowire samples utilizing a variety of methods. Phase formation, mechanical homogeneity, optical characteristics, and topographical structure and roughness were all thoroughly examined at various stresses. MgO hardness values ranged from 1.4 to 3.2 GPa, whereas MgO-ZrO₂ ranged from 0.38 to 1.2 GPa. The I–V parameter study was a further step in the examination of the heterostructure’s electrical properties. The structural, morphological, optical, mechanical, and electrical properties of the MgO-ZrO₂ heterostructure were all thoroughly described using these techniques. Full article

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

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20 pages, 3502 KiB

Open AccessArticle

Neural Network-Based Kinetic Model for Antisolvent Crystallization of Benzophenone: Construction, Validation, and Mechanistic Interpretation

by Yafei Dong, Shutian Xuanyuan, Chuang Xie, Ying Sun, Xiaomeng Zhou and Yuanhang Wang

Crystals 2025, 15(5), 464; https://doi.org/10.3390/cryst15050464 - 15 May 2025

Viewed by 87

Abstract

The emergence of artificial neural networks and the widespread application of process analytical technology (PAT) have founded a robust foundation for neural network applications in crystallization research. This study investigated benzophenone antisolvent crystallization kinetics through online monitoring of the crystallization process via PAT [...] Read more.

The emergence of artificial neural networks and the widespread application of process analytical technology (PAT) have founded a robust foundation for neural network applications in crystallization research. This study investigated benzophenone antisolvent crystallization kinetics through online monitoring of the crystallization process via PAT tools and kinetics fitting via neural networks. The antisolvent crystallization process was simulated by integrating network-based kinetics with population balance. The findings suggest that benzophenone exhibits size-independent growth in water–methanol systems. The neural network-based model demonstrates improved performance (a consistent 50 ± 5% enhancement in prediction accuracy (R²) over empirical kinetic models) in predicting crystallization kinetics. Furthermore, the network-based process model achieved remarkable agreement with the experimental crystal size distribution, showing smaller deviation (1.1%), less than that of traditional empirical models (5.29%). This work proposed a robust crystallization process model combining PAT tools and artificial neural networks, enabling rapid crystallization kinetics determination and accurate process simulations. Full article

(This article belongs to the Special Issue Crystallization Process and Simulation Calculation, Third Edition)

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22 pages, 6755 KiB

Open AccessArticle

Structural, Mechanical, and Tribological Properties of Molybdenum-Doped Diamond-like Carbon Films

by Hassan Zhairabany, Hesam Khaksar, Edgars Vanags, Krisjanis Smits, Anatolijs Sarakovskis and Liutauras Marcinauskas

Crystals 2025, 15(5), 463; https://doi.org/10.3390/cryst15050463 - 15 May 2025

Viewed by 163

Abstract

Non-hydrogenated diamond-like carbon (DLC) films and molybdenum-doped diamond-like carbon (Mo-DLC) films were deposited by direct current magnetron sputtering. The formation was carried out on Si (100) wafers. The influence of molybdenum concentration and deposition temperature on the surface morphology, chemical composition, type of [...] Read more.

Non-hydrogenated diamond-like carbon (DLC) films and molybdenum-doped diamond-like carbon (Mo-DLC) films were deposited by direct current magnetron sputtering. The formation was carried out on Si (100) wafers. The influence of molybdenum concentration and deposition temperature on the surface morphology, chemical composition, type of chemical bonds, friction force at nanoscale, and nanohardness of the DLC coatings were investigated by atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and nanoindenter, respectively. The concentration of molybdenum in the films varies from 1.2 at.% to 10.3 at.%. The increase in molybdenum content promotes the graphitization of DLC films, lowering the sp³ site fraction and increasing the oxygen content, which contributes to the reduction in nanohardness (by 21%) of the DLC films. The decrease in the synthesis temperature from 235 °C to 180 °C enhanced the oxygen amount up to 20.4 at.%. The sp³ site fraction and nanohardness of the Mo-DLC films were enhanced with the reduction in the deposition temperature. The film deposited at a substrate temperature of 235 °C exhibited the lowest friction coefficient (CoF) of 0.03, where its molybdenum concentration was 1.2 at.%. The decline in the synthesis temperature increased the CoF of the Mo-DLC films up to seven times. Full article

(This article belongs to the Special Issue Advances in Diamond Crystals and Devices)

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12 pages, 3635 KiB

Open AccessArticle

Design of Multifunctional Polarization Waveplates Based on Thermal Phase-Change Metasurfaces

by Bo Cheng, Yuxiao Zou, Zihui Ge, Longfeng Lv, Taohua Liang, Kunpeng Zhai and Guofeng Song

Crystals 2025, 15(5), 462; https://doi.org/10.3390/cryst15050462 - 14 May 2025

Viewed by 146

Abstract

The switching function of traditional waveplates necessitates mechanical replacement or the superimposition of multiple waveplates, which gives rise to a complex system and a large volume. We have devised a multifunctional micro-waveplate based on the COMSOL simulation platform (v5.6), which concurrently integrates the [...] Read more.

The switching function of traditional waveplates necessitates mechanical replacement or the superimposition of multiple waveplates, which gives rise to a complex system and a large volume. We have devised a multifunctional micro-waveplate based on the COMSOL simulation platform (v5.6), which concurrently integrates the compact nature of metasurfaces and the dynamic regulatory features of phase-change materials. When the phase-change material is in the crystalline phase, the metasurface possesses the functionality of a half-waveplate (HWP) and is capable of performing chirality inversion of circularly polarized light within the wavelength range of 1.45 μm to 1.52 μm and 1.56 μm to 1.61 μm. When the phase-change material is in the amorphous phase, the metasurface serves as a quarter-waveplate (QWP) and can achieve the conversion between linear and circular polarization through a 90° phase delay. The phase-change metasurface breaks through the constraint of fixed functions of traditional optical waveplates, facilitating the development of optical systems towards miniaturization, intelligence, and low power consumption and providing a crucial technical route for the next generation of photonic integration and dynamic optical applications. Full article

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

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12 pages, 23111 KiB

Open AccessArticle

A Rare Yellow Diamond: Reconstruction of the Possible Geological History

by Isabella Pignatelli and Cristiano Ferraris

Crystals 2025, 15(5), 461; https://doi.org/10.3390/cryst15050461 - 14 May 2025

Viewed by 211

Abstract

In this study, a rare 3.49-carat yellow diamond was analyzed to reconstruct the geological processes that led to its distinctive form. The diamond exhibits growth and dissolution features, indicating a complex history. To preserve the sample’s integrity, non-destructive analytical techniques—including VIS, UV–Vis–NIR, and [...] Read more.

In this study, a rare 3.49-carat yellow diamond was analyzed to reconstruct the geological processes that led to its distinctive form. The diamond exhibits growth and dissolution features, indicating a complex history. To preserve the sample’s integrity, non-destructive analytical techniques—including VIS, UV–Vis–NIR, and IR spectroscopy—were employed. The yellow coloration of the diamond is attributed to the presence of N3 and N2 defects. Additionally, other defects such as N₃VH⁰ centers and platelets were detected; however, the latter do not contribute to the coloration. The observations of the etch pits and surface microreliefs suggest that the diamond underwent size reduction due to dissolution events, which also altered its crystal habit over time. The diamond’s initial mixed-habit morphology evolved into a more complex one through a series of growth and dissolution processes that began during mantle storage. Furthermore, the presence of brown surface stains indicates radiation damage, likely acquired during its residence in alluvial deposits at the Earth’s surface. Full article

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

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14 pages, 5810 KiB

Open AccessArticle

CO₂ Absorption on Cu-Doped Graphene, a DFT Study

by Juan Oseas López Fuentes, Roxana Mitzayé del Castillo Vázquez and Juan Manuel Ramirez-de-Arellano

Crystals 2025, 15(5), 460; https://doi.org/10.3390/cryst15050460 - 14 May 2025

Viewed by 343

Abstract

We studied the interaction between a Cu-doped graphene layer and a CO₂ molecule, using DFT, ab initio calculations, and the pseudopotential formalism. We used the Quantum ESPRESSO code package, with the PBE XC functional expression and the semiempirical Grimme’s DFT-D3 Van der [...] Read more.

We studied the interaction between a Cu-doped graphene layer and a CO₂ molecule, using DFT, ab initio calculations, and the pseudopotential formalism. We used the Quantum ESPRESSO code package, with the PBE XC functional expression and the semiempirical Grimme’s DFT-D3 Van der Waals correction. We found that the Cu atom, being absorbed in a C vacancy on the graphene surface, has a catalytic effect on the absorption of CO₂ in said surface. The Van der Waals correction calculations showed that the CO₂ is physisorbed, with an adsorption energy of −0.1786 eV. Our results are congruent with previously published results. The Cu-doped graphene surface could be suitable for the development of a CO₂ sensor. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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15 pages, 3922 KiB

Open AccessArticle

First-Principles Investigation of the Effect of Vacancy Defects and Carbon Impurities on Thermal Conductivity of Uranium Mononitride (UN)

by Yulin Lan, Tianhao Rui, Zhuangzhuang Ma, Linyuan Lu, Yunhao Wang, Yang Yu, Mingxuan Deng, Tianxing Lan, Zhekang Zhao, Junjie Wang, Congyi Li and Haibin Zhang

Crystals 2025, 15(5), 459; https://doi.org/10.3390/cryst15050459 - 14 May 2025

Viewed by 165

Abstract

Uranium mononitride (UN) is a promising nuclear fuel with a high melting point, high thermal conductivity, and low coefficient of thermal expansion. Theoretical studies of UN can provide insights on its thermal transport mechanism, which is of great significance for the design and [...] Read more.

Uranium mononitride (UN) is a promising nuclear fuel with a high melting point, high thermal conductivity, and low coefficient of thermal expansion. Theoretical studies of UN can provide insights on its thermal transport mechanism, which is of great significance for the design and application of UN fuel. During the processing and operation, crystal defects and impurities, such as vacancies and carbon impurities, potentially arise in the nuclear fuel, which probably affect the thermomechanical properties of UN. To figure out the effect of vacancy defects and carbon impurities on the thermal conductivity of UN, density functional theory and Boltzmann transport theory are applied to conduct a theoretical investigation on the mechanical and thermal properties of ideal and defective UN. The calculated results show that in the case of UN with a U or N vacancy, both the lattice and electronic thermal conductivity are decreased, compared with the ideal case. With a carbon atom occupying the N site in the lattice, the electronic thermal conductivity is reduced but the lattice thermal conductivity is increased. Combining the results of lattice and electronic thermal conductivity, the total thermal conductivities of three defective states are lower than the ideal UN. The thermal conductivities of UN with a U vacancy (13.91 W/mK), N vacancy (15.36 W/mK), and a carbon atom occupying the N site (15.14 W/mK) are, respectively, reduced by 25.7%, 18.0%, and 19.2%, in comparison with ideal result (18.73 W/mK) at 1000 K. Full article

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