Crystals

15 pages, 4756 KB

Open AccessArticle

Correlating Ten Composition-, Lattice- and Microstructure-Derived Descriptors with Compressive Yield Strength in Previously Reported Single-Phase BCC Refractory High-Entropy Alloys

by Longchao Zhuo, Hanyue Li, Bingqing Chen, Jiacheng Sun and Zhaozong Zhang

Crystals 2026, 16(8), 537; https://doi.org/10.3390/cryst16080537 (registering DOI) - 16 Aug 2026

Abstract

Composition criteria for refractory high-entropy alloys (RHEAs) reliably predict whether a candidate composition forms a single-phase body-centred-cubic (BCC) solid solution, but not which BCC-confirmed composition will be strongest. Here we revisit seven previously reported RHEA compositions on freshly arc-melted material of our own, [...] Read more.

Composition criteria for refractory high-entropy alloys (RHEAs) reliably predict whether a candidate composition forms a single-phase body-centred-cubic (BCC) solid solution, but not which BCC-confirmed composition will be strongest. Here we revisit seven previously reported RHEA compositions on freshly arc-melted material of our own, confirm each as single-phase BCC using full-spectrum X-ray diffraction re-indexing, and screen ten descriptors obtainable before mechanical testing against their room-temperature compressive yield strength: five compositional (mean atomic radius r⁻, mixing enthalpy ΔH_mix, atomic-size mismatch δ, VEC, and melting point T_m), two lattice-scale (Nelson–Riley parameter a₀ and Williamson–Hall apparent microstrain ε) and three microstructural (KAM, ELM₁₅, and grain ECD). Only ΔH_mix ranks the strengths, and its direction inverts the usual expectation: the less negative the mixing enthalpy, the stronger the alloy. Refractoriness carries no ranking information, and the most refractory member, NbMoTaW, is second weakest of six. At n = 6 only a perfect ranking reaches a Benjamini–Hochberg q below 0.05 across ten descriptors, so the q of 0.167 obtained here measures cohort resolution: a ranking of this magnitude clears the corrected threshold from eight alloys upwards. Mean atomic radius separately predicts a₀ across all seven alloys. Full article

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

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17 pages, 20588 KB

Open AccessArticle

Wollastonite–Silicon Nitride Ceramic Composites: Microstructure, Mechanical Performance and Bioactivity

by João Vinícius Barros Reis, Thiago dos Santos Ferreira, João Marcos Oliveira Moura Salgado Costa, Claudinei Santos, Flávio Machado de Souza Carvalho, Patrick de Lima Gomes, Dolores Ribeiro Ricci Lazar and Cecilia Chaves Guedes-Silva

Crystals 2026, 16(8), 536; https://doi.org/10.3390/cryst16080536 (registering DOI) - 16 Aug 2026

Abstract

Silicon nitride (Si₃N₄) is an advanced structural ceramic with considerable potential for load-bearing biomedical applications owing to its excellent mechanical properties and favorable biological response. In this study, the effect of wollastonite (CaSiO₃) addition on the microstructure, [...] Read more.

Silicon nitride (Si₃N₄) is an advanced structural ceramic with considerable potential for load-bearing biomedical applications owing to its excellent mechanical properties and favorable biological response. In this study, the effect of wollastonite (CaSiO₃) addition on the microstructure, mechanical performance, and in vitro bioactivity of Si₃N₄–CaSiO₃ ceramic composites was investigated. Composites containing 5–30 wt.% wollastonite were prepared by pressureless sintering at 1800 °C for 1 h and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), density measurements, nanoindentation, Vickers hardness, fracture toughness, compressive strength, and simulated body fluid (SBF) immersion tests. Increasing the wollastonite resulted in progressive densification up to 20 wt.% CaSiO₃, resulting in a maximum relative density of 96%, together with complete α→β-Si₃N₄ transformation and the development of elongated β-Si₃N₄ grains. The composition containing 20 wt.% wollastonite exhibited optimum mechanical performance, achieving a hardness of approximately 13 GPa, fracture toughness of ~5.5 MPa·m^1/2, and compressive strength of ~2840 MPa. The results demonstrate that wollastonite plays a multifunctional role in Si₃N₄ ceramic composites by promoting densification during sintering and improving in vitro bioactivity while maintaining high mechanical performance. These findings highlight the potential of Si₃N₄–CaSiO₃ ceramic composites as promising bioactive structural materials for load-bearing orthopedic and dental applications. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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23 pages, 8758 KB

Open AccessArticle

Freeze–Thaw Durability and Pb Leaching Control of Graphene-Assisted MICP-Stabilized Pb-Contaminated Loess: Coupled Hydro-Environmental and Geotechnical Performance

by Yunxiao Jin, Shixu Zhang, Longping Luo, Siqi Hong and Jianmei Zhang

Crystals 2026, 16(8), 535; https://doi.org/10.3390/cryst16080535 - 14 Aug 2026

Abstract

Freeze–thaw cycling can strongly disturb the pore-water environment, soil fabric, and contaminant mobility of heavy-metal-contaminated loess, thereby threatening the long-term effectiveness of stabilization treatments in seasonally frozen regions. This study investigated the coupled hydro-environmental and geotechnical performance of Pb-contaminated loess (untreated control group, [...] Read more.

Freeze–thaw cycling can strongly disturb the pore-water environment, soil fabric, and contaminant mobility of heavy-metal-contaminated loess, thereby threatening the long-term effectiveness of stabilization treatments in seasonally frozen regions. This study investigated the coupled hydro-environmental and geotechnical performance of Pb-contaminated loess (untreated control group, CK) treated with microbially induced calcium carbonate precipitation (MICP), graphene (GR)-assisted MICP, and graphene oxide (GO)-assisted MICP under controlled freeze–thaw cycles. One-dimensional consolidation tests, toxicity characteristic leaching procedure (TCLP) tests, zeta-potential measurements, X-ray fluorescence (XRF), and scanning electron microscopy (SEM) were conducted to evaluate compressibility evolution, Pb leaching behavior, interfacial electrochemical characteristics, mineralogical changes, and microstructural mechanisms. After 9 days of mineralization, MICP reduced the Pb leaching concentration from 38.05 to 23.00 mg L⁻¹, achieving a 39.55% reduction compared with untreated Pb-contaminated loess. Freeze–thaw cycling increased the susceptibility of treated loess to structural degradation and pore collapse, especially under medium to high vertical stresses. Nevertheless, the void ratio generally followed the order of CK > MICP > MICP + GR > MICP + GO under comparable loading and freeze–thaw conditions, indicating progressively enhanced resistance to compressive deformation. GR-assisted MICP showed an optimum dosage of approximately 1.0%, beyond which Pb leaching increased because of sheet restacking, agglomeration, and non-uniform biomineralization. In contrast, under up to 13 freeze–thaw cycles, GO-assisted MICP maintained the lowest void ratio and the most stable Pb immobilization performance among all treatments, demonstrating improved resistance against freeze–thaw-induced structural degradation. The results suggest that GO-assisted MICP can simultaneously improve Pb leaching control and soil-fabric stability, providing a promising low-carbon strategy for remediating heavy-metal-contaminated loess exposed to water-mediated freeze–thaw disturbance. Full article

(This article belongs to the Special Issue Advanced Research in Biomineralization)

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13 pages, 8469 KB

Open AccessArticle

Thermal Distortion Behavior and Microstructural Evolution of Ti-6Al-1.3V-0.9Fe Alloy

by Caibao Guo, Hai Gu, Zhonggang Sun, Jie Zhang and Guoqing Dai

Crystals 2026, 16(8), 534; https://doi.org/10.3390/cryst16080534 - 14 Aug 2026

Abstract

The Ti-6Al-4V alloy is widely used in aerospace and deep-sea applications due to its exceptional strength and corrosion resistance. However, its application is often constrained by high deformation resistance and a narrow hot-working temperature window, primarily attributed to its heat and mass transfer [...] Read more.

The Ti-6Al-4V alloy is widely used in aerospace and deep-sea applications due to its exceptional strength and corrosion resistance. However, its application is often constrained by high deformation resistance and a narrow hot-working temperature window, primarily attributed to its heat and mass transfer characteristics. To address these limitations, a novel Ti-6Al-1.3V-0.9Fe alloy was designed with an equivalent molybdenum content. In this study, Gleeble thermal simulation tests were conducted to investigate the impact of Fe on the hot deformation behavior under various conditions and to identify the optimal processing window for this alloy. The effects of deformation temperature and strain rate on the flow stress curves and peak stress were systematically analyzed, along with the role of Fe in microstructural evolution during hot deformation. The results demonstrate that the addition of Fe significantly refines the grain size of the Ti-6Al-1.3V-0.9Fe alloy. As expected, the flow stress decreases with increasing deformation temperature and increases at higher strain rates. Under high-temperature and low-strain-rate conditions, the alloy exhibits steady-state flow behavior, indicating improved hot workability. Based on the constitutive modeling, the apparent activation energy (Q) for hot deformation was calculated to be 503.81 kJ/mol. Finally, the optimal hot-working parameters for the Ti-6Al-1.3V-0.9Fe alloy were identified as a temperature range of 760 °C to 860 °C and a strain rate between 0.01 and 0.16 s⁻¹. Full article

(This article belongs to the Topic Advanced Ceramics: Processing, Properties, and Applications)

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19 pages, 4762 KB

Open AccessArticle

Coloration and Genesis of Calcite-Dominated Jade from Xinjiang, China: Evidence from Spectroscopy, U-Pb Dating, and C-O Isotope

by Yunxi Zhu, Yi Zhao, Siying Li, Zheyi Zhao and Gexue Zhao

Crystals 2026, 16(8), 533; https://doi.org/10.3390/cryst16080533 - 14 Aug 2026

Abstract

Carbonate jade has emerged as a recently recognized commercial variety in the Chinese gemstone market. Systematic gemological and mineralogical investigations on carbonate jade, however, remain very scarce. Three Xinjiang calcite-dominated jade samples were investigated by using Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, ultraviolet-visible [...] Read more.

Carbonate jade has emerged as a recently recognized commercial variety in the Chinese gemstone market. Systematic gemological and mineralogical investigations on carbonate jade, however, remain very scarce. Three Xinjiang calcite-dominated jade samples were investigated by using Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, ultraviolet-visible (UV-Vis) absorption spectroscopy, microbeam X-ray fluorescence (Micro-XRF) spectrometry, trace element analysis, in situ U-Pb dating, and C-O isotope analysis. The orange-red color originates from staining by hematite and magnetite inclusions, while the green color is produced by d-d electronic transitions of lattice-bound Fe³⁺ and Mn²⁺. The provenance comparison reveals systematic differences in trace element compositions between the Xinjiang carbonate jade and Pakistani Lvwen stone: the Xinjiang samples are characterized by extremely low Cu and Sr contents, whereas the Pakistani Lvwen stone has high Cu, Mn and Sr contents, and low Fe content. The U-Pb age obtained for the Xinjiang carbonate jade sample coincides with a Late Cretaceous rapid cooling event. Enriched light rare earth element (LREE) and C-O isotope (δ¹³C_V-PDB = −1.19–2.21‰, δ¹⁸O_V-SMOW = 15.00–20.01‰) signatures indicate that the carbonate-precipitating fluids were derived from marine carbonate wall rocks. These findings provide new mineralogical and geochemical constraints on the coloration mechanism, provenance, and fluid evolution of carbonate jade from Xinjiang. Full article

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

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18 pages, 3434 KB

Open AccessArticle

Self-Supporting PAM/PEDOT:PSS Thermoelectric Devices Enhanced by Metasurface Radiative Cooling

by Yujia Liu, Ye Yuan, Zheng Li, Xinli Liu, Zitong Zang, Yang Liu, Xianbo Nian and Chunsheng Guo

Crystals 2026, 16(8), 532; https://doi.org/10.3390/cryst16080532 - 14 Aug 2026

Abstract

The rapid development of wearable electronics has created a demand for flexible, lightweight, and sustainable power-supply technologies. The persistent temperature difference between the human body and the environment provides a low-grade thermal source for thermoelectric energy harvesting. However, traditional flexible thermoelectric devices still [...] Read more.

The rapid development of wearable electronics has created a demand for flexible, lightweight, and sustainable power-supply technologies. The persistent temperature difference between the human body and the environment provides a low-grade thermal source for thermoelectric energy harvesting. However, traditional flexible thermoelectric devices still face limited self-supporting capabilities and difficulties in maintaining sufficiently low cold-side temperatures. Here, we designed a passively radiative-cooled thermoelectric film (PRT film) by integrating a PAM/PEDOT:PSS self-supporting thermoelectric composite layer with a polymer metamaterial radiative cooling (PMRC) film. The PAM/PEDOT:PSS layer serves as a self-supporting thermoelectric conversion component for harvesting low-grade heat, while the PMRC film layer acts as a passive cold-side regulator without energy input to lower the cold-side temperature and enhance the temperature gradient. By optimizing the PAM content, the PAM/PEDOT:PSS composite material with 85 wt% PAM achieved the highest power factor of 72.3 μW m⁻¹ K⁻². Under a temperature difference of 39 °C, the optimized PAM/PEDOT:PSS sample provided an open-circuit voltage of 0.47 V, a maximum output power of 1.1 μW, and a power density of 11.2 μW cm⁻². According to the temperature-difference enhancement measured in experiments and the independently obtained load characteristics, the integration of PMRC films is expected to increase the maximum output power from 1.1 to 1.4 μW, with the corresponding power density rising from 11.2 to 14.25 μW cm⁻², representing a 27.2% enhancement. This work demonstrates the feasibility of passive radiative cold-side regulation in enhancing low-level thermoelectric energy harvesting for wearable applications. Full article

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

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12 pages, 1918 KB

Open AccessArticle

Method for Controlling the Exposure of (312) Crystal Plane in Ni₁₂P₅ Nanoparticles and Its Impact on the Catalytic Dechlorination Activity of Trichloroethylene

by Guojun Yuan, Yajun Gao, Hongfang Li, Lei Cheng, Wenjuan Sun and Haolu Sun

Crystals 2026, 16(8), 531; https://doi.org/10.3390/cryst16080531 - 14 Aug 2026

Abstract

Transition metal phosphides (TMPs) have gained significant attention from researchers in the field of catalytic hydrogenation due to their excellent properties. However, existing studies have rarely explored the targeted regulation of the degree of crystal plane exposure of the Ni₁₂P₅ [...] Read more.

Transition metal phosphides (TMPs) have gained significant attention from researchers in the field of catalytic hydrogenation due to their excellent properties. However, existing studies have rarely explored the targeted regulation of the degree of crystal plane exposure of the Ni₁₂P₅ catalyst. It is difficult to significantly enhance the performance of this catalyst in the hydrogenation dechlorination (HDC) reaction of trichloroethylene by this strategy. This study proposes a regulatory approach: changing the ratio of ethylene glycol to water to precisely control the exposure ratio of the high-index (312) crystal plane of the Ni₁₂P₅ catalyst. Combined with the performance tests of trichloroethylene hydrogenation dechlorination at different reaction temperatures, the intrinsic relationship between the step atoms generated during the formation of the (312) crystal plane and the active sites of the catalyst was clarified. The study also utilized multiple characterization methods such as transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) to conduct a comprehensive property analysis of the prepared catalytic materials. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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15 pages, 3987 KB

Open AccessArticle

A Dual-Criterion System for Surface-Localized States Identification: Application to Al(001) Surface

by Xihui Liang and Dah-An Luh

Crystals 2026, 16(8), 530; https://doi.org/10.3390/cryst16080530 - 13 Aug 2026

Abstract

Angle-resolved photoemission spectroscopy (ARPES) clearly resolves surface-localized (SL) states, yet conventional density functional theory (DFT) band structures from slab calculations do not readily distinguish weakly confined SL states on surfaces such as Al(001), as traditional layer-threshold criteria fail for surfaces with long surface-state [...] Read more.

Angle-resolved photoemission spectroscopy (ARPES) clearly resolves surface-localized (SL) states, yet conventional density functional theory (DFT) band structures from slab calculations do not readily distinguish weakly confined SL states on surfaces such as Al(001), as traditional layer-threshold criteria fail for surfaces with long surface-state decay lengths. We establish a dual-criterion scheme using the surface ratio R and the localization integral L weighted by the inelastic mean free path (IMFP) to quantitatively distinguish SL states: R quantifies the surface-projected charge fraction, while L incorporates the photoelectron IMFP to mimic ARPES surface sensitivity, both evaluated within a fully converged 81-layer Al(001) slab that eliminates artificial inter-surface coupling. Band structures color-coded by R and L intuitively highlight SL states as bright yellow-white bands against red bulk backgrounds. Our calculations show that continuum SL features arise from multi-band hybridization (sharp surface resonances). Notably, R and L alone cannot separate absolute surface states from resonances. All DFT calculations were performed using the PBEsol exchange-correlation functional within the GGA framework, the PAW formalism, and an 81-layer Al(001) slab model. This work reveals the electronic nature of surface features on Al(001) and provides a quantitative SL-state identification tool that is conceptually transferable to other crystalline surfaces. Full article

(This article belongs to the Special Issue Density Functional Theory (DFT) in Crystalline Material)

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9 pages, 7914 KB

Open AccessCommunication

Phase Spheroidization and Solid-Solution Strengthening of Extruded Mg-Si-Zn-Ca-Y Alloy Induced by Low-Temperature Annealing

by Yuxin Liu, Wenhui Tong, Xinyu Wu and Jiale Li

Crystals 2026, 16(8), 529; https://doi.org/10.3390/cryst16080529 - 12 Aug 2026

Abstract

Microstructural evolution and mechanical properties of as-extruded Mg-2.5Si-4Zn-0.7Ca-1Y alloys were characterized under diverse heat treatment conditions. An optimal regime of 200 °C for 12 h emerged, delivering a peak Vickers hardness of ~100 HV0.2. After heat treatment, substantial dissolution of Zn into the [...] Read more.

Microstructural evolution and mechanical properties of as-extruded Mg-2.5Si-4Zn-0.7Ca-1Y alloys were characterized under diverse heat treatment conditions. An optimal regime of 200 °C for 12 h emerged, delivering a peak Vickers hardness of ~100 HV0.2. After heat treatment, substantial dissolution of Zn into the α-Mg matrix occurred and Ca/Y-rich intermetallics underwent spheroidization. The microstructural changes facilitated the improvement of ultimate tensile strength (UTS) at 200 °C from ~160 MPa to ~200 MPa, while the elongation decreased from ~18% to ~6%. The enhanced high-temperature strength derives from Zn solid-solution strengthening and spheroidization of the Ca/Y-rich network phase, with a possible additional contribution from Y redistribution near the Mg₂Si-containing regions. Full article

(This article belongs to the Special Issue Performance and Processing of Metal Materials)

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34 pages, 8905 KB

Open AccessReview

Linking Dislocation Mobility, Compatible Heterogeneity and Service Stability in NbTaV-Containing and Related BCC Refractory High- and Medium-Entropy Alloys

by Longchao Zhuo, Yingliang Zhang, Bingqing Chen, Jiacheng Sun, Hao Wang and Zhaozong Zhang

Crystals 2026, 16(8), 528; https://doi.org/10.3390/cryst16080528 - 12 Aug 2026

Abstract

Refractory high-entropy and compositionally complex alloys are routinely compared by nominal composition and as-processed phase, yet processing changes the material that is actually tested. This is a critical, mechanism-led narrative review rather than a systematic review; the databases, complete search strings, screening sequence, [...] Read more.

Refractory high-entropy and compositionally complex alloys are routinely compared by nominal composition and as-processed phase, yet processing changes the material that is actually tested. This is a critical, mechanism-led narrative review rather than a systematic review; the databases, complete search strings, screening sequence, inclusion and exclusion criteria, and evidence-grading rubric are reported so that coverage and selection bias can be assessed independently. This review synthesizes 186 publications around the NbTaV compositional core and compares alloys through directly measurable features of the processed state: interstitial content, local chemical order, grain-boundary chemistry, defect and grain architecture, phase morphology, compositional gradients and surfaces. Every source is assigned to a compositional tier and graded along four evidence axes: 96 of the 186 sources report Nb–Ta–V-containing states (Tier I), 58 are body-centered cubic refractory comparators (Tier II) and 32 are transferred-mechanism analogues (Tier III), and only 14 Tier I sources supply direct tensile, fracture or tensile-creep measurements. This asymmetry, rather than any disagreement between compositions, is the field’s binding evidence constraint. Direct tensile, fracture, and creep measurements are kept separate from compression, hardness, calculation, and screening evidence. This separation reconciles observations that otherwise appear to conflict: oxygen can strengthen or embrittle; lattice distortion can raise strength while lowering dislocation mobility; local order can harden the alloy, redirect defects or precede decomposition; and second phases help only within morphology- and service-specific compatibility windows. The strongest tensile behavior is obtained when mobile plasticity carriers are preserved, and interstitials, interfaces and phase continuity are simultaneously controlled. High-temperature, environmental, and irradiation performance depend additionally on the transition from the as-manufactured condition to the state that evolves during service. Quantitative matching tolerances for the convergent-state falsification test, service-condition-specific validation hierarchies, ordinal scoring rules for the phase-compatibility map, and a source-level audit of every quantitatively compared value are provided so that the framework can be tested and the synthesis independently checked. Full article

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

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13 pages, 3393 KB

Open AccessArticle

Energetics and Quasiparticle Band Structures of SiC Polytypes and the Single Shockley Stacking Fault in 4H-SiC from RPA and GW Calculations

by Taswar Iqbal, Soon-Ku Hong, Sung Beom Cho, Trong Si Ngo, Raouf Hayyak, Mee-Hi Choi, Moonkyong Na and Young Heon Kim

Crystals 2026, 16(8), 527; https://doi.org/10.3390/cryst16080527 - 11 Aug 2026

Abstract

A comprehensive beyond density functional theory study of the structural, energetic, and electronic properties of the technologically most relevant SiC polytypes 3C, 2H, 4H, and 6H-SiC, together with the single Shockley-type stacking fault (1SSF or 31SSF) in 4H-SiC, was conducted. Lattice constants computed [...] Read more.

A comprehensive beyond density functional theory study of the structural, energetic, and electronic properties of the technologically most relevant SiC polytypes 3C, 2H, 4H, and 6H-SiC, together with the single Shockley-type stacking fault (1SSF or 31SSF) in 4H-SiC, was conducted. Lattice constants computed at the PBEsol and HSE06 level match experimental values within 0.1% accuracy. Total energies evaluated at the random-phase approximation level yield a physically consistent hierarchy of polytypes with 3C-SiC as the most stable phase, which is in agreement with low-temperature experimental results. Quasiparticle band gaps computed with both the single-shot G0W0@PBE and the partially self-consistent GW0@PBE formulations quantitatively match well with the experimental values. The band structure of 31SSF reveals fault-induced sub-gap band splitting at the M point of 0.21 eV at the GGA level, which increases to 0.28 eV upon G0W0 correction. To our knowledge, this provides the first GW-level treatment of the 31SSF electronic structure in 4H-SiC. These results collectively provide a many-body perturbation theory (MBPT) level reference dataset for SiC polytypes and the commonly found stacking fault in 4H-SiC. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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21 pages, 8737 KB

Open AccessArticle

Parameter Screening and Optimization for DL-Methionine Cooling Crystallization Using Response Surface Methodology

by Hetao Huang, Mingfei Gao, Zhengju Liu, Guanyu Chen, Chaoli Jiang and Zhiliang Cheng

Crystals 2026, 16(8), 526; https://doi.org/10.3390/cryst16080526 - 11 Aug 2026

Abstract

Cooling crystallization of DL-methionine requires the joint control of crystallization yield and bulk density because operating conditions that favor one response may impair the other. Here, single-factor experiments, Plackett–Burman screening, and a three-factor Box–Behnken response-surface design were combined to identify a local operating [...] Read more.

Cooling crystallization of DL-methionine requires the joint control of crystallization yield and bulk density because operating conditions that favor one response may impair the other. Here, single-factor experiments, Plackett–Burman screening, and a three-factor Box–Behnken response-surface design were combined to identify a local operating window. Stirring speed, crystallization time, and solution pH were retained for response-surface modeling. The quadratic models for crystallization yield and bulk density were significant, with R² values of 0.9910 and 0.9892, respectively, and nonsignificant lack-of-fit terms. Multi-response optimization selected a stirring speed of approximately 332 r/min, a crystallization time of 1.47 h, and a pH of 5.55. Three validation experiments produced yields of 48.98–49.57% and bulk densities of 0.2925–0.3035 g/mL, with relative errors below 5% compared with the model predictions. X-ray diffraction showed no detectable change in the principal DL-methionine crystal phase across representative products. X-ray photoelectron spectroscopy further showed closely matched near-surface C 1s, N 1s, O 1s, and S 2p features between the raw material and the product obtained under the optimized conditions. The sodium nitroprusside assay gave total methionine contents of 99.64–99.79% for the raw material and five representative products; for the model-selected product, the colorimetric result (99.79%) agreed with the amino acid analyzer result (99.93%) to within 0.14%. The combined PB–BBD/RSM workflow therefore supports local parameter selection within the tested design space while maintaining the principal crystal phase, near-surface chemical-state profile, and total methionine content of the recovered product. Full article

(This article belongs to the Section Industrial Crystallization)

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19 pages, 6851 KB

Open AccessArticle

Structural and Optical Investigation of Sol–Gel-Derived TiO₂ Films Deposited on Transparent Substrates

by Tatyana Ivanova, Antoaneta Harizanova and Nikolay Petkov

Crystals 2026, 16(8), 525; https://doi.org/10.3390/cryst16080525 - 10 Aug 2026

Abstract

In the present work, thin TiO₂ films were obtained by the sol–gel spin-coating method on glass and ITO-covered glass substrates. The crystallization evolution of the thin films was studied by the X-ray Diffraction (XRD) technique. The results indicate that the films’ crystalline [...] Read more.

In the present work, thin TiO₂ films were obtained by the sol–gel spin-coating method on glass and ITO-covered glass substrates. The crystallization evolution of the thin films was studied by the X-ray Diffraction (XRD) technique. The results indicate that the films’ crystalline structure was greatly affected by substrate type. X-ray photoelectron spectroscopy (XPS) revealed the chemical states of the TiO₂ films and proved the formation of TiO₂ on ITO substrates. Field Emission Scanning Electron Microscopy (FESEM) showed that the TiO₂ films deposited on the ITO glass possessed a uniform and homogeneous surface morphology. The influence of optical properties (transmittance, reflectance, and optical band gap) on substrate type, the number of layers and annealing temperatures was determined. Spectroscopic data confirmed high transparency of the TiO₂ films obtained on ITO substrates as the transmittance in the visible spectral range was close to 85%. The obtained results reveal that thin TiO₂ films on ITO substrates can be an excellent candidate for photovoltaic and optoelectronic applications. Full article

(This article belongs to the Special Issue Research on Complex Oxide Nanomaterials)

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2 pages, 125 KB

Open AccessCorrection

Correction: Wang et al. A Novel Energetic Nitroform Salt Derived from Bis-(Triazolyl)-Furoxan. Crystals 2025, 15, 960

by Fawei Wang, Jiapeng Wang, Zihu Wang, Jianhua Wang and Yucun Liu

Crystals 2026, 16(8), 524; https://doi.org/10.3390/cryst16080524 - 10 Aug 2026

Abstract

To avoid potential misinterpretation, the caption of Figure 6 and the text preceding it have been revised to clearly indicate that Figure 6a displays the sulfate salt of compound 1 [...] Full article

13 pages, 2613 KB

Open AccessArticle

Spectroscopic Characteristics of Blue Calcite and the Origin of Its Coloration and Luminescence

by Jingying Lv, Qingfeng Guo, Shuo Ran and Xin Zhang

Crystals 2026, 16(8), 523; https://doi.org/10.3390/cryst16080523 - 9 Aug 2026

Abstract

Natural blue calcite is relatively rare, and its coloration and luminescence mechanisms have not been systematically established. In this study, four natural blue calcite samples from China were comprehensively characterized using mineralogical testing, X-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning electron microscopy [...] Read more.

Natural blue calcite is relatively rare, and its coloration and luminescence mechanisms have not been systematically established. In this study, four natural blue calcite samples from China were comprehensively characterized using mineralogical testing, X-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet–visible spectroscopy (UV-Vis), photoluminescence (PL), and electron paramagnetic resonance (EPR). XRD confirms single-phase trigonal calcite (space group R-3c). EPMA detects minor Mg, Fe, Cu, and Sr, with smaller-radius Mg²⁺, Fe²⁺, and Cu²⁺ being the main contributors to the contraction through isomorphous substitution for Ca²⁺. UV-Vis spectra show characteristic absorptions at 270 nm and 340 nm related to lattice defects with a broad emission band centered at 480 nm in the PL spectra. EPR detects a CO₂⁻ radical center (g = 2.003), and the same signal is also observed in the colorless sample. The colorless sample also contains the same CO₂⁻ radicals, indicating that these radicals alone do not account for the blue coloration. A broad 480 nm blue-violet fluorescence band is observed in the four blue samples under 405 nm excitation. These findings provide a spectroscopic and crystallographic basis for distinguishing natural blue calcite from analogous materials and for understanding the origin of its color and luminescence. Full article

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

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9 pages, 6205 KB

Open AccessArticle

Time-of-Flight Secondary Ion Mass Spectrometry Characterization and Elemental Distribution of Potassium Dihydrogen Phosphate Crystals Under Laser Irradiation

by Xiangcao Li, Baoan Liu, Hongjie Xue, Yuan Xie and Xin Ju

Crystals 2026, 16(8), 522; https://doi.org/10.3390/cryst16080522 - 8 Aug 2026

Abstract

This study used time-of-flight secondary ion mass spectrometry (TOF-SIMS) to comprehensively analyze the elemental composition, ion distribution, and signal variations in potassium dihydrogen phosphate (KDP) crystals at various sputtering depths after laser irradiation. Positive ion mass spectra were employed to identify the characteristic [...] Read more.

This study used time-of-flight secondary ion mass spectrometry (TOF-SIMS) to comprehensively analyze the elemental composition, ion distribution, and signal variations in potassium dihydrogen phosphate (KDP) crystals at various sputtering depths after laser irradiation. Positive ion mass spectra were employed to identify the characteristic ions K⁺, Ca⁺, Fe⁺, Si⁺, and P⁺. These ions were assigned to their corresponding chemical species. Large-area two-dimensional chemical mapping and maximum count/total count (MC/TC) analysis combined and showed clear depth-dependent trends; all detected ions had significantly higher MC and TC values at larger sputtering depths. At a depth of 1.3 nm, Fe-related and O-related ion signals exhibited overlapping localized hotspots, whereas Ca species showed ring-like enrichment at the edges of the damage pits. These changes are attributed to the laser-induced decomposition of KDP crystals, in which metal inclusions absorb laser energy, generate localized high temperature and pressure, and promote material ejection and ion redistribution. These findings provide direct experimental evidence for understanding laser-induced elemental redistribution in KDP crystals and offer useful guidance for further optimization of their performance. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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28 pages, 6470 KB

Open AccessReview

Plasma-Enhanced Atomic Layer Deposition of III-Nitride Thin Films and Heterostructures: Mechanisms and Applications

by Sanjie Liu, Zilong Zeng, Yongyong Cao, Zhenyi Deng, Xinjie Li, Zixin Liang, Rongjie Feng, Jiaping Long, Yu Liu, Ruifan Tang and Xinhe Zheng

Crystals 2026, 16(8), 521; https://doi.org/10.3390/cryst16080521 - 8 Aug 2026

Abstract

Group III-nitride semiconductors (GaN, AlN, InN) serve as foundational materials for modern optoelectronics, high-frequency microelectronics, and next-generation energy harvesting devices. However, traditional high-temperature epitaxy (>700 °C) introduces severe thermal stress, high dislocation densities, and fundamental incompatibility with flexible substrates or CMOS back-end-of-line (BEOL) [...] Read more.

Group III-nitride semiconductors (GaN, AlN, InN) serve as foundational materials for modern optoelectronics, high-frequency microelectronics, and next-generation energy harvesting devices. However, traditional high-temperature epitaxy (>700 °C) introduces severe thermal stress, high dislocation densities, and fundamental incompatibility with flexible substrates or CMOS back-end-of-line (BEOL) processes. Plasma-enhanced atomic layer deposition (PEALD) provides a disruptive, ultra-low thermal budget (<300 °C) pathway for atomic-scale precision growth and conformal coating. This review systematically summarizes recent frontiers in PEALD-synthesized Group III-nitrides and 2D/3D polar heterostructures. First, we dissect the microscopic nucleation kinetics, surface bond reconstruction, and impurity suppression mechanisms across diverse substrates, including Si, sapphire, quartz, metals, and flexible polymers. Next, we highlight 2D template-assisted van der Waals epitaxy on graphene and MoS2, and elucidate polarization-driven dipole interactions and band alignment engineering at 2D/3D polar interfaces (e.g., α-In₂Se₃, Janus MoSSe). Furthermore, we comprehensively discuss innovative applications in advanced photovoltaics (as electron transport and passivation layers in perovskite and quantum dot-sensitized solar cells), silicon-based microcavity lasers, high-electron-mobility transistors (HEMTs), and flexible multimodal sensors. Finally, key technological challenges—including the low-thermal-budget paradox, wafer-scale uniformity, and deposition throughput—are addressed alongside future perspectives in area-selective ALD and neuromorphic computing, presenting a cohesive blueprint from underlying physics to macroscopic system integration. Full article

(This article belongs to the Special Issue Advances in Wide Bandgap Semiconductor Materials)

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11 pages, 10416 KB

Open AccessArticle

TEM Analysis of Orientational Domain Evolution Triggered by Structural Phase Transition in Bi_0.25Ca_0.75MnO₃ Ceramics

by Changjiang Nie, Hengxue Wang, Zhihong Chen, Junyan Wang, Huaqing Xiao and Yang Liu

Crystals 2026, 16(8), 520; https://doi.org/10.3390/cryst16080520 - 7 Aug 2026

Abstract

The structural phase transition and associated orientational domain configurations in perovskite-type Bi_xCa_1−xMnO₃ ceramics were investigated in this work. A series of Bi_xCa_1−xMnO₃ solid solutions with x = 0.05, 0.25, 0.33 were [...] Read more.

The structural phase transition and associated orientational domain configurations in perovskite-type Bi_xCa_1−xMnO₃ ceramics were investigated in this work. A series of Bi_xCa_1−xMnO₃ solid solutions with x = 0.05, 0.25, 0.33 were synthesized, and Bi_0.25Ca_0.75MnO₃ with moderate orthorhombic lattice distortion was selected as the representative sample for systematic TEM characterization. Upon cooling from high temperature, the material undergoes a symmetry-lowering transition from the cubic phase with Pm

\bar{3}

m space group to the orthorhombic phase with Pnma space group. Selected-area electron diffraction (SAED) and bright-field TEM observations reveal the formation of multiple orientational domains, including both 90° and 120° configurations, within individual grains. High-resolution TEM (HRTEM) further confirms the coexistence of three distinct domain orientations at the atomic scale, with well-defined lattice fringes and domain boundaries. The reciprocal-space orientational relationships derived from SAED patterns demonstrate that these domains originate from the symmetry breaking of the parent cubic lattice during the phase transition. These findings provide direct crystallographic insight into the domain structures of BCMO, and such microstructural features are essential for revealing the structural stability and intrinsic functional behaviors of BCMO manganites. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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20 pages, 12098 KB

Open AccessArticle

Provenance and Genesis of Gem-Quality Rutile Revealed by Integrated Spectroscopic, Geochemical, and U-Pb Geochronological Signatures

by Junting Mu, Siying Li, Yi Zhao, Gexue Zhao and Zheyi Zhao

Crystals 2026, 16(8), 519; https://doi.org/10.3390/cryst16080519 - 6 Aug 2026

Abstract

Rutile is an oxide mineral widely distributed in igneous, metamorphic, and sedimentary rocks; it crystallizes in the tetragonal system. Trace-element abundances in rutile are influenced by the host-rock composition, redox conditions and crystallization history. Rutile exhibits high refractive index, strong dispersion, and adamantine [...] Read more.

Rutile is an oxide mineral widely distributed in igneous, metamorphic, and sedimentary rocks; it crystallizes in the tetragonal system. Trace-element abundances in rutile are influenced by the host-rock composition, redox conditions and crystallization history. Rutile exhibits high refractive index, strong dispersion, and adamantine luster. Its enrichment in high field strength elements (HFSEs) can be used to trace its formation environment. Owing to its inclusion-poor, compositionally uniform characteristics, rutile is particularly well-suited to in situ U-Pb geochronology. By integrating spectroscopic analysis, trace-element geochemistry, and U-Pb geochronology, this study systematically characterizes nine rutile samples from Madagascar, Pakistan, and Brazil, establishing a multi-dimensional scheme for origin discrimination. Spectroscopic analyses reveal that the infrared reflection band near 670 cm⁻¹ varies systematically with provenance. It appears as a broad, strong band in Madagascar samples, becomes weaker and narrower in Brazilian samples, and is partially absent in Pakistani samples. The Eg Raman mode of Brazilian rutile is slightly left-shifted and exhibits lower intensity, indicating a distinct lattice strain state. Analyzed samples occupy well-separated compositional fields on Nb–V, V–Ta, Zr–Hf and Nb–Ta binary variation plots. Specifically, Pakistani samples are characterized by high Nb and Ta contents and relatively lower V contents than the Brazilian and Madagascar samples. Madagascar samples show pronounced W enrichment and very low Cr. Brazilian samples display elevated Cr, V, higher U contents and more radiogenic Pb isotope compositions. Zr–W systematics and Cr–Nb bivariate discrimination allow inference of geological genesis. The Madagascar rutile is of hydrothermal origin, whereas the Pakistani and Brazilian rutile are metamorphic, derived from felsic/pelitic and mafic protoliths, respectively. LA-ICP-MS U-Pb geochronology yields a lower-intercept age of 504 ± 13 Ma (MSWD = 1.1) for the Madagascar sample (MD-1). This concordant, low-common-Pb age corresponds to the Pan-African orogeny and suggests strong potential as an in-situ U-Pb dating reference material. The Brazilian and Pakistani samples yield lower-intercept ages of 486 ± 53 Ma and 36.8 ± 2.9 Ma, respectively. However, the larger data scatter precludes their use as reference materials. Full article

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

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