Crystals

2 pages, 114 KB

Open AccessCorrection

Correction: Zhou et al. Dynamic Recrystallization Behavior and Prediction Model of an Ultra-High-Strength Nickel-Based Corrosion-Resistant Alloy During Hot Deformation. Crystals 2026, 16, 424

by Dadi Zhou, Qubo He, Gang Meng, Pujie Gou, Wei Jiang and Tengzhong Zhang

Crystals 2026, 16(9), 591; https://doi.org/10.3390/cryst16090591 - 16 Sep 2026

Abstract

Qubo He was not included as an author in the original publication [...] Full article

(This article belongs to the Special Issue Investigation of Microstructural and Properties of Steels and Alloys)

2 pages, 115 KB

Open AccessCorrection

Correction: Zhou et al. Development of a Flow-Stress Constitutive Model and Hot-Processing Window for a High-Nb, Ultra-High-Strength (205 ksi) Nickel-Based Corrosion-Resistant Alloy. Crystals 2026, 16, 447

by Dadi Zhou, Qubo He, Gang Meng, Wei Jiang, Tengzhong Zhang and Zhiqiang Wang

Crystals 2026, 16(9), 590; https://doi.org/10.3390/cryst16090590 - 16 Sep 2026

Abstract

Addition of an Author [...] Full article

(This article belongs to the Special Issue Investigation of Microstructural and Properties of Steels and Alloys)

15 pages, 15450 KB

Open AccessArticle

Angular-Response Balancing in 4H-SiC Diffractive Waveguides Using Oppositely Oriented Slanted Gratings

by Shiyang Hou, Runsheng Zheng, Chenghang Yang, Xiaoqing Liu, Yangyang Liang and Qingbo Li

Crystals 2026, 16(9), 589; https://doi.org/10.3390/cryst16090589 - 13 Sep 2026

Abstract

High-index 4H-silicon carbide (4H-SiC) provides a larger waveguide k-space than conventional glass and is therefore attractive for wide field-of-view (FOV) diffractive augmented reality waveguides. However, the angular response of a slanted grating is asymmetric. For one grating-vector direction, the diffraction efficiency remains high [...] Read more.

High-index 4H-silicon carbide (4H-SiC) provides a larger waveguide k-space than conventional glass and is therefore attractive for wide field-of-view (FOV) diffractive augmented reality waveguides. However, the angular response of a slanted grating is asymmetric. For one grating-vector direction, the diffraction efficiency remains high over a wide positive-angle range but decreases rapidly at negative angles, leading to nonuniform image brightness over a broad field. Reversing the grating vector reverses this response. The field is therefore divided at 0°, with the positive and negative FOV channels assigned to two mirror-related slanted-grating domains with opposite grating vectors. The grating parameters for the red (648 nm), green (548 nm), and blue (448 nm) wavelengths were optimized separately using particle swarm optimization. Their angular diffraction responses were calculated by rigorous coupled-wave analysis and then introduced into Zemax for system-level ray tracing. At 548 nm, the optimized 4H-SiC, n = 1.8 glass, and n = 2.0 glass gratings provided effective angular bandwidths of approximately 88°, 31°, and 37°, respectively. Under the same 4H-SiC material and system conditions, the +G/−G arrangement reduced the root-mean-square (RMS) irradiance nonuniformity from approximately 40.3% to 32.8% and increased the effective fill factor from 40.8% to 61.5% compared with the single-+G configuration. In a separate system-level comparison, the optimized n = 1.8 glass and 4H-SiC models yield RMS irradiance nonuniformities of 44.0% and 32.8% and effective fill factors of 46.1% and 61.5%, respectively. These results connect the broad angular response of the optimized 4H-SiC grating with the system-level balancing produced by opposite grating-vector assignment. The optimized grating parameters and detector-plane response maps also provide a computational basis for subsequent fabrication and experimental validation of the proposed 4H-SiC waveguide design. Full article

(This article belongs to the Special Issue Key Crystal Materials for Optoelectronic Devices: Structure Regulation, Performance Optimization, and Device Applications)

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12 pages, 4205 KB

Open AccessArticle

Fabrication of High-Performance Flexible Perovskite Solar Cells Based on Composite Modification Layers

by Luxiao Sang, Yujing Tang, Yunsheng Lin, Bolin Song, Haitao Zhang and Tengteng Li

Crystals 2026, 16(9), 588; https://doi.org/10.3390/cryst16090588 - 11 Sep 2026

Abstract

Flexible perovskite solar cells (F-PSCs) exhibit broad application prospects due to their lightweight and bendable properties. However, uneven substrates and thermal–mechanical deformation during bending hinder the growth of high-quality perovskite films. Meanwhile, stress accumulation at the interfaces of flexible devices aggravates carrier recombination, [...] Read more.

Flexible perovskite solar cells (F-PSCs) exhibit broad application prospects due to their lightweight and bendable properties. However, uneven substrates and thermal–mechanical deformation during bending hinder the growth of high-quality perovskite films. Meanwhile, stress accumulation at the interfaces of flexible devices aggravates carrier recombination, resulting in deteriorated device performance and stability. Thus, we construct a poly(methyl methacrylate) (PMMA)/[1,1′-biphenyl]-4-carboxamidine hydrochloride (BPhADCl) composite modification layer to synergistically optimize the performance of F-PSCs. Specifically, PMMA can passivate interfacial defects and buffer bending stress. BPhADCl enables the in situ formation of 2D perovskite as nucleation sites to induce the growth of high-quality films, and the formed 2D/3D perovskite heterojunction can block moisture erosion and improve device stability. The optimized F-PSC delivers a champion power conversion efficiency (PCE) of 24.33%, remarkably higher than 20.71% of the control device. After 5000 bending cycles at a bending radius of 5 mm, the device retains 83% of its initial PCE. Moreover, the unencapsulated device maintains 91% of its original efficiency after 1100 h storage under ambient conditions. Full article

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13 pages, 3890 KB

Open AccessArticle

Kinetic Analysis of Simultaneous Leaching of Lithium, Iron, and Phosphorus from LiFePO₄ Cathodes of Spent Batteries

by Haiqing Xu, Zhihong Zhang and Huaijin Zeng

Crystals 2026, 16(9), 587; https://doi.org/10.3390/cryst16090587 - 11 Sep 2026

Abstract

The high-value recovery of valuable components from spent LiFePO₄ (LFP) batteries is of considerable significance for both resource recycling and environmental conservation. This study systematically investigates the simultaneous sulfuric acid leaching of Li, Fe, and P from spent LFP cathode materials, integrating [...] Read more.

The high-value recovery of valuable components from spent LiFePO₄ (LFP) batteries is of considerable significance for both resource recycling and environmental conservation. This study systematically investigates the simultaneous sulfuric acid leaching of Li, Fe, and P from spent LFP cathode materials, integrating process optimization with kinetic analysis. The effects of acid concentration, temperature, and stirring speed on the leaching behavior of Li, Fe, and P were evaluated to elucidate the underlying kinetic mechanisms. The results demonstrated that under optimal conditions—namely, a sulfuric acid concentration of 2.0 mol/L, a leaching temperature of 60 °C, and a stirring speed of 300 r/min—the leaching rates of Li, Fe, and P all exceeded 99.5%. Kinetic analysis revealed a diffusion-controlled leaching mechanism well described by the Avrami model, with a selective dissolution sequence of Li > Fe > P. The leaching of Li, Fe, and P exhibited apparent activation energies of 9.56 kJ/mol, 14.83 kJ/mol, and 12.82 kJ/mol, respectively. These findings provide theoretical support for the leaching and resource recovery of Li, Fe, and P from spent LFP cathode materials. Full article

(This article belongs to the Special Issue Sustainable Hydrometallurgical Recycling from Spent Lithium-Ion Batteries and Industrial Solid Wastes)

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21 pages, 11187 KB

Open AccessArticle

Deposition Kinetics and Structural Transformations in WC–12Co and Cr₃C₂–NiCr HVOF Coatings Depending on Powder Dispersion

by Duman Askerzhanov, Nurzhan Serikbekuly, Bauyrzhan Rakhadilov, Zarina Satbayeva, Aikyn Erboluly, Vladislav Kots, Zhanel Bakyt, Aidar Kengesbekov, Ainur Zhassulan and Rinat Kussainov

Crystals 2026, 16(9), 586; https://doi.org/10.3390/cryst16090586 - 10 Sep 2026

Abstract

HVOF coatings based on tungsten and chromium carbides are widely used in aerospace, energy, and oil and gas industries. However, the selection between the wear resistance of WC–Co and the corrosion resistance of Cr₃C₂–NiCr is often hindered by a [...] Read more.

HVOF coatings based on tungsten and chromium carbides are widely used in aerospace, energy, and oil and gas industries. However, the selection between the wear resistance of WC–Co and the corrosion resistance of Cr₃C₂–NiCr is often hindered by a lack of systematic data on the effect of powder particle size. In this study, WC–12Co and Cr₃C₂–NiCr coatings were deposited onto 12Kh18N10T stainless steel substrates by HVOF spraying using three particle size fractions: <20, 20–32, and 32–40 μm. Individual spray parameters were selected for each material to ensure high-quality deposition (standoff distance 350 mm, one pass for WC–12Co; 250 mm, two passes for Cr₃C₂–NiCr). The influence of powder particle size distribution on coating properties was investigated using a comprehensive set of methods, including scanning electron microscopy, X-ray diffraction with Rietveld quantitative phase analysis, microhardness testing, tribological testing, electrochemical measurements, and numerical modeling of particle in-flight motion. It was found that the 20–32 μm fraction is optimal for both materials. Different degradation mechanisms were identified: for WC–Co, decarburization of WC with the formation of W₂C and η-phases dominates (maximum for the <20 μm fraction); for Cr₃C₂–NiCr, oxidation and carbide dissociation prevail (in the <20 μm fraction—13.7% Cr₂O₃ and 38.6% Cr₇C₃), leading to low coating thickness (~16 μm) due to loss of ductility and wettability. Numerical modeling confirmed that the high velocity of fine Cr₃C₂–NiCr particles (~680–720 m/s) does not compensate for their overheating, whereas for WC–12Co all fractions have velocities above the critical threshold, but coarse particles (32–40 μm) give porosity up to 3.15% due to insufficient deformation. Corrosion tests showed that under spraying conditions optimized for each material, the Cr₃C₂–NiCr coatings (corrosion rate 0.066–0.102 mm/year) are an order of magnitude superior in corrosion resistance to WC–12Co coatings (corrosion rate 0.353–0.651 mm/year), owing to the passivation of the γ-Ni(Cr) matrix; for WC–Co, the main protective barrier is provided by the structural density. Full article

(This article belongs to the Section Materials for Energy Applications)

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10 pages, 5333 KB

Open AccessArticle

Regulation of Crystal Packing and Energetic Performance of TNT Derivatives by Bromine Substitution

by Zi-Bo Zhang, Su-Ming Jing, Tian-Yi Wen and Yi-Wei Zhang

Crystals 2026, 16(9), 585; https://doi.org/10.3390/cryst16090585 - 10 Sep 2026

Abstract

Improving the energetic performance of established explosives through rational structural modification provides an alternative strategy for the development of entirely new energetic molecules. In this work, bromine substitution was employed to regulate the solid-state properties of TNT derivatives, and two compounds, 3-bromo-2,4,6-trinitrotoluene (3-BrTNT) [...] Read more.

Improving the energetic performance of established explosives through rational structural modification provides an alternative strategy for the development of entirely new energetic molecules. In this work, bromine substitution was employed to regulate the solid-state properties of TNT derivatives, and two compounds, 3-bromo-2,4,6-trinitrotoluene (3-BrTNT) and 3,5-dibromo-2,4,6-trinitrotoluene (3,5-BrTNT), were synthesized and characterized. Single-crystal X-ray diffraction revealed that different bromination patterns lead to distinct crystal structures and packing characteristics. Electrostatic potential analysis and Hirshfeld surface analysis further revealed that bromine substitution modifies molecular surface characteristics and intermolecular contact distributions within the crystals. Compared with 3-BrTNT, 3,5-BrTNT exhibits a higher crystal density of 2.312 g cm⁻³ and improved calculated detonation performance, with a detonation velocity of 7915 m s⁻¹ and a detonation pressure of 31.86 GPa. Meanwhile, both brominated derivatives exhibit reduced impact sensitivity compared with TNT. These results demonstrate that the bromination pattern, rather than bromine incorporation alone, plays an important role in regulating crystal structures and energetic properties. This study provides insight into substitution-pattern-controlled crystal engineering as a strategy for optimizing TNT-based energetic materials. Full article

(This article belongs to the Section Crystal Engineering)

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15 pages, 4608 KB

Open AccessArticle

Classification of 2D-GIWAXS Images of Highly Textured Molecular Thin Films Towards Indexation: Triclinic Lattices

by Detlef-M. Smilgies

Crystals 2026, 16(9), 584; https://doi.org/10.3390/cryst16090584 - 9 Sep 2026

Abstract

Low-symmetry triclinic lattices, as formed by molecular thin films, are conveniently characterized by grazing-incidence wide-angle X-ray scattering (GIWAXS). These films are often highly textured with a specific crystallographic plane

(H K L)

parallel to the surface and thus form uniaxial powders. [...] Read more.

Low-symmetry triclinic lattices, as formed by molecular thin films, are conveniently characterized by grazing-incidence wide-angle X-ray scattering (GIWAXS). These films are often highly textured with a specific crystallographic plane

(H K L)

parallel to the surface and thus form uniaxial powders. A classification scheme is presented that lays the groundwork for determination of the surface unit cell and indexing such complex scattering images. After identifying a first surface unit cell, methods are discussed for normalizing the lattice constants and further reduction of the unit cell. Full article

(This article belongs to the Special Issue Crystals: 15th Anniversary)

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8 pages, 11444 KB

Open AccessArticle

Controllable Synthesis and Characterization of Ordered 0D and 1D Antimony Nanostructures on Ag₂Sb/Ag(111)

by Ping Zhang, Jingxi Tan, Jiebin Chen, Huiru Liu, Xiaohuai Wang, Xiang Wang, Chen Ma, Shaoxiang Sheng, Lan Chen, Youming Lu and Yun Li

Crystals 2026, 16(9), 583; https://doi.org/10.3390/cryst16090583 - 7 Sep 2026

Abstract

By precisely controlling the growth temperature and coverage, we successfully synthesized a highly ordered zero-dimensional (0D) Sb₁₈ nanocluster and a one-dimensional (1D) Janus Sb nanochain on the Ag₂Sb/Ag(111) surface. Using scanning tunneling microscopy (STM) in combination with density functional theory [...] Read more.

By precisely controlling the growth temperature and coverage, we successfully synthesized a highly ordered zero-dimensional (0D) Sb₁₈ nanocluster and a one-dimensional (1D) Janus Sb nanochain on the Ag₂Sb/Ag(111) surface. Using scanning tunneling microscopy (STM) in combination with density functional theory (DFT) calculations, we characterized their atomic structures and found that the alloy substrate plays a significant role in stabilizing these configurations. Our findings not only demonstrate the feasibility of controllably synthesizing low-dimensional Sb nanostructures on metallic substrates but also provide valuable insights into their growth mechanism. Full article

(This article belongs to the Special Issue Advanced Research in 2D Semiconductors)

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23 pages, 3830 KB

Open AccessArticle

It Is Getting Packed in Here: Synthesis, Structure and Biological Activity of Halogenated 1,10-Phenanthroline Epoxide Derivatives

by Julian Polle, Florian Mai, Marcus Layh, Verena Spiegler and Marian Hebenbrock

Crystals 2026, 16(9), 582; https://doi.org/10.3390/cryst16090582 - 7 Sep 2026

Abstract

1,10-Phenanthroline derivatives are versatile ligands whose structural and biological properties can be tuned by targeted functionalization. Here, a series of 2,9-dihalogenated 1,10-phenanthroline derivatives and their corresponding 5,6-epoxy-5,6-dihydro analogs were synthesized and characterized. Single-crystal X-ray diffraction experiments reveal pronounced substituent-dependent packing motifs. While 2,9-diiodo-1,10-phenanthroline [...] Read more.

1,10-Phenanthroline derivatives are versatile ligands whose structural and biological properties can be tuned by targeted functionalization. Here, a series of 2,9-dihalogenated 1,10-phenanthroline derivatives and their corresponding 5,6-epoxy-5,6-dihydro analogs were synthesized and characterized. Single-crystal X-ray diffraction experiments reveal pronounced substituent-dependent packing motifs. While 2,9-diiodo-1,10-phenanthroline forms a sandwich-herringbone arrangement dominated by short I···I contacts, the phenanthroline epoxides exhibit π-stacking combined with C–H···O and C–H···halogen interactions. For the brominated and iodinated epoxides, additional halogen···halogen contacts generate extended supramolecular networks. Biological evaluation in selected cell lines showed that both halogenation and epoxidation reduce the cytotoxicity of the parent phenanthroline scaffold, whereas no significant effects on Pseudomonas aeruginosa growth or biofilm formation were observed. These results demonstrate how simple structural modifications of 1,10-phenanthroline influence both solid-state organization and biological activity, providing insight into the role of halogen substituents and epoxide formation in phenanthroline-based systems. Full article

(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals (2nd Edition))

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19 pages, 10941 KB

Open AccessArticle

Concentration-Dependent Precursor Engineering with Butylammonium Acetate for Inverted Triple-Cation Perovskite Solar Cells

by Hanhong Zhang, Shaolong Chen and Yushan Yang

Crystals 2026, 16(9), 581; https://doi.org/10.3390/cryst16090581 - 6 Sep 2026

Abstract

Butylammonium acetate (BAAc) was investigated as a concentration-dependent precursor additive for inverted triple-cation perovskite solar cells based on FA_0.80Cs_0.07MA_0.13PbI_2.64Br_0.39. BAAc loadings ranging from 0 to 7 mol% were systematically compared to determine how [...] Read more.

Butylammonium acetate (BAAc) was investigated as a concentration-dependent precursor additive for inverted triple-cation perovskite solar cells based on FA_0.80Cs_0.07MA_0.13PbI_2.64Br_0.39. BAAc loadings ranging from 0 to 7 mol% were systematically compared to determine how moderate and excessive additive concentrations influence film formation, defect behavior, and device operation. At 3 mol% BAAc, the mean equivalent-circle grain diameter increased from 0.508 to 0.719 μm, and the median increased from 0.495 to 0.688 μm, while cross-sectional SEM confirmed a comparable absorber thickness of 500 ± 20 nm across the series. The PbI₂-to-perovskite diffraction peak height ratio decreased from 0.2691 to 0.0427, and the intensity-weighted photoluminescence lifetime increased from 230.2 to 350.0 ns. Light-intensity-dependent open-circuit voltage, impedance spectroscopy, thermal admittance spectroscopy, and space-charge-limited current measurements consistently indicated reduced trap-assisted recombination and transport loss at this concentration. In the EIS analysis, BAAc-3 showed the lowest transport resistance (222.17 ± 9.52 Ω) and the highest recombination resistance (8.211 ± 0.061 kΩ); all principal resistance parameters had relative standard errors below 10%, although systematic high-frequency residuals limit quantitative interpretation of the transport CPE. The champion BAAc-3 device reached 23.37% efficiency, compared with 20.42% for the control, and the 50-device mean increased from 19.63 ± 0.45% to 22.77 ± 0.30%. At 7 mol%, the morphological and electrical trends reversed and the champion efficiency decreased to 19.34%, which defines an over-treatment boundary. The 30-day dry–dark storage and 120 min maximum-power-point tests provide comparative, short-duration stability evidence. The concentration dependence is consistent with a literature-supported working model of precursor coordination and ammonium–halide interactions, without constituting direct spectroscopic identification of a specific complex. Full article

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23 pages, 8534 KB

Open AccessArticle

Effect of a Stoichiometric Trefoil-like Rotational Reconstruction on the Electronic and Optical Properties of WS₂ and WSe₂ Monolayers

by Daulet Sergeyev, Gulbanu Serikbayeva and Ainur Duisenova

Crystals 2026, 16(9), 580; https://doi.org/10.3390/cryst16090580 - 6 Sep 2026

Abstract

Structural defects provide an effective means of tailoring the electronic and optical properties of two-dimensional transition-metal dichalcogenides. In this work, the structural, electronic, and polarization-resolved optical properties of pristine WS₂ and WSe₂ monolayers and their stoichiometric trefoil-like rotational reconstructions were investigated [...] Read more.

Structural defects provide an effective means of tailoring the electronic and optical properties of two-dimensional transition-metal dichalcogenides. In this work, the structural, electronic, and polarization-resolved optical properties of pristine WS₂ and WSe₂ monolayers and their stoichiometric trefoil-like rotational reconstructions were investigated using density functional theory. The reconstruction was generated through a local 60° bond rotation without removing or adding atoms and therefore differs fundamentally from the experimentally observed chalcogen-deficient T₁(3DV) defect. Electronic-structure calculations were performed using the PBE-GGA + U and SOGGA approaches, with noncollinear spin–orbit coupling included in the latter, while the optical response was evaluated within the independent-particle Kubo-Greenwood formalism. Structural relaxation revealed two distinct regimes. In WS₂, the reconstruction produced a largely compensated redistribution of W–S bond lengths, with the mean distance remaining nearly unchanged, whereas WSe₂ exhibited a net expansion of the W–Se coordination network and substantially stronger out-of-plane buckling. The reconstruction introduced additional W 5d–chalcogen p states near the band edges and markedly reduced the electronic band gaps. For WS₂, the gap decreased from 1.87 to 1.55 eV within DFT + U and from 1.96 to 1.46 eV within SOGGA. A substantially stronger response was obtained for WSe₂, for which the corresponding gaps decreased from 1.533 to 0.751 eV and from 1.657 to 0.645 eV. The reconstructed monolayers exhibited pronounced optical anisotropy, red-shifted absorption edges, spectral broadening, and additional low-energy in-plane optical transitions. These effects were particularly strong in WSe₂, where the calculated optical response extended into the near-infrared region. The results demonstrate that the electronic and optical response to a stoichiometric trefoil-like reconstruction is strongly chalcogen-dependent and is governed by the interplay among local geometrical distortion, W 5d–chalcogen p hybridization, and spin–orbit coupling. Full article

(This article belongs to the Special Issue Recent Advances in Graphene and Other Two-Dimensional Materials (2nd Edition))

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15 pages, 4979 KB

Open AccessArticle

Effects of Aluminium Coated with Stainless Steel on the Nutritional Quality of Tomato Products

by Steluța Radu and Ștefan Lucian Toma

Crystals 2026, 16(9), 579; https://doi.org/10.3390/cryst16090579 - 5 Sep 2026

Abstract

This study evaluated the storage stability of tomato juice, paste, and purée packaged in conventional aluminium containers (ACs) and aluminium containers coated with a food-grade stainless steel layer (ASSCs). The objective was to determine whether the stainless steel coating could reduce aluminium ion [...] Read more.

This study evaluated the storage stability of tomato juice, paste, and purée packaged in conventional aluminium containers (ACs) and aluminium containers coated with a food-grade stainless steel layer (ASSCs). The objective was to determine whether the stainless steel coating could reduce aluminium ion migration, preserve the physicochemical and nutritional quality of tomato products during storage, and decrease the need for antioxidant, antifungal, and acidifying additives. The stainless steel coating improved the barrier performance of the Al substrate by reducing its porosity from 6.0% to 3.8%. During storage, tomato products in ACs exhibited a marked decrease in acidity (7.65–4.07 g/100 g), whereas samples stored in ASSCs showed a smaller reduction (7.65–5.98 g/100 g), indicating enhanced chemical stability. Increasing NaCl concentrations promoted Al migration, reaching 26.4 mg/kg in AC but only 9.2 mg/kg in ASSC. The vitamin C content remained nearly unchanged (2.09–2.04 mg/100 g), while total polyphenols decreased slightly (110.13–98.81 mg/100 g). Mineral analysis (Al, Cr, Mn, Ni, Zn, Fe, and Ca) confirmed higher metal concentrations in AC-stored samples, whereas aluminium migration was effectively minimised in ASSCs. These findings demonstrate that stainless steel-coated aluminium provides superior corrosion resistance, limits metal transfer, preserves the physicochemical and antioxidant quality of the tomato products, and represents a promising packaging material for extending shelf life while reducing the need for food additives. Full article

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

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8 pages, 2112 KB

Open AccessCommunication

Optical Properties of Se-Excess Ge₂Sb₂Se_xTe₁ (4.23 < x < 4.97) Phase-Change Thin Films

by Congzheng Ji and Fengang Zheng

Crystals 2026, 16(9), 578; https://doi.org/10.3390/cryst16090578 - 4 Sep 2026

Abstract

In this study, Se-excess Ge₂Sb₂Se_xTe₁ (GSST) thin films were synthesized via magnetron co-sputtering. The crystal structure, surface morphology, complex refractive index, and bandgap of the Se-excess GSST thin films were systematically investigated. Owing to the formation [...] Read more.

In this study, Se-excess Ge₂Sb₂Se_xTe₁ (GSST) thin films were synthesized via magnetron co-sputtering. The crystal structure, surface morphology, complex refractive index, and bandgap of the Se-excess GSST thin films were systematically investigated. Owing to the formation of higher-energy Sb–Se bonds at an annealing temperature of 350 °C, grain refinement occurred (the average dendrite trunk width decreased from 0.64 μm to 0.37 μm). Consequently, the extinction coefficient (k) in the crystalline state was reduced to 0.17, resulting in a figure of merit (FOM) of 8.76 at the telecommunications C-band wavelength of 1550 nm. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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24 pages, 30801 KB

Open AccessArticle

Heat-Induced Color Evolution and Structural Stability of Pinkish-Orange and Red Tourmalines: An Integrated Colorimetric, Spectroscopic, and Chemical Study

by Aumaparn Phlayrahan and Nantharat Bunnag

Crystals 2026, 16(9), 577; https://doi.org/10.3390/cryst16090577 - 4 Sep 2026

Abstract

This study investigated the effects of progressive step-heating (300–500 °C) and direct heating (500 °C) on pinkish-orange and red tourmalines using colorimetric, spectroscopic, and chemical analyses. Heating progressively modified visible absorption and color, with treatment at 500 °C generally increasing lightness (L* [...] Read more.

This study investigated the effects of progressive step-heating (300–500 °C) and direct heating (500 °C) on pinkish-orange and red tourmalines using colorimetric, spectroscopic, and chemical analyses. Heating progressively modified visible absorption and color, with treatment at 500 °C generally increasing lightness (L*) and substantially decreasing chroma (C*), accompanied by weakening of the broad absorption near 520 nm while strong pleochroism was retained. Chemical analyses revealed substantial compositional variability, particularly in Mn and Fe, although elemental abundance alone did not account for the observed optical responses. Color evolution was associated with changes in overlapping electronic absorption features, but the underlying microscopic processes could not be uniquely assigned to specific transition-metal ions or oxidation-state changes. Fourier transform infrared (FTIR) spectroscopy showed preservation of the principal framework-related vibrational features up to 500 °C, with no evidence of major structural disruption. Within the present step-heating series, 400 °C produced an intermediate outcome characterized by measurable lightening and desaturation while retaining more of the original pink-to-red chromatic component than after treatment at 500 °C, which produced substantially greater desaturation. Full article

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

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15 pages, 29814 KB

Open AccessArticle

Structural Insights into the N-Terminus and a Flexible P-x-P Loop near the Active Site of a Class III Aminotransferase

by Jisub Hwang, Hackwon Do and Jun Hyuck Lee

Crystals 2026, 16(9), 576; https://doi.org/10.3390/cryst16090576 - 3 Sep 2026

Abstract

Class III aminotransferases represent a structurally and functionally unique subgroup. However, the contribution of specific loop elements to their active-site architecture and cofactor-dependent structural transitions remain underexplored. We elucidated the structural framework underlying the catalytic function of class III fold Pyridoxal 5′-phosphate-dependent aminotransferase [...] Read more.

Class III aminotransferases represent a structurally and functionally unique subgroup. However, the contribution of specific loop elements to their active-site architecture and cofactor-dependent structural transitions remain underexplored. We elucidated the structural framework underlying the catalytic function of class III fold Pyridoxal 5′-phosphate-dependent aminotransferase from the Antarctic bacterium Hymenobacter sp. PAMC 26554 (HyAT), and report its crystal structure at 2.31 Å resolution. The structure revealed a canonical class III fold organized as a functional homotetramer. Structural analysis identified a proline-containing motif (P-x-P) within the α10-α11 loop, which induces intrinsic disorder at the active-site entrance in the apo-form and revealed that a cooperative disorder-to-order transition is requisite for active-site assembly upon cofactor binding. We propose that this flexible loop region may be involved in modulating substrate access. Notably, this proline motif was conserved in homologs from Hyperthermophiles, despite the cold-adapted nature of HyAT. This convergence implies a common evolutionary strategy where the geometric constraints of proline are exploited to decouple local active-site dynamics from global scaffold stability, thereby addressing the stability–activity trade-off across diverse thermal environments. Our findings provide new molecular insights into the structural dynamics of class III aminotransferases and highlight evolutionary strategies for tuning enzyme flexibility in extreme environments. Full article

(This article belongs to the Section Biomolecular Crystals)

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22 pages, 2652 KB

Open AccessArticle

Tuning the Electronic Properties of a Nitro- and Cyano-Functionalized Benzothienoquinolizinium Salt as Potential Organic N-Type Semiconductor: Experimental and Theoretical Study

by Andrés Aracena, Kerry Wrighton-Araneda, Katherine Pezet, Diego Vilches, Felipe A. Angel, Ihan Chandía, César Zúñiga, Sebastián Elgueta and Javiera González

Crystals 2026, 16(9), 575; https://doi.org/10.3390/cryst16090575 - 2 Sep 2026

Abstract

A new nitro- and cyano-functionalized, tetradecyl-substituted benzothienoquinolizinium tetrafluoroborate was synthesized through oxidative photocyclisation of a pyridinium precursor and evaluated as a potential small molecule N-type organic semiconductor. The precursor and the photocyclised salts were characterized by UV–Vis absorption spectroscopy, DSC, ¹H and [...] Read more.

A new nitro- and cyano-functionalized, tetradecyl-substituted benzothienoquinolizinium tetrafluoroborate was synthesized through oxidative photocyclisation of a pyridinium precursor and evaluated as a potential small molecule N-type organic semiconductor. The precursor and the photocyclised salts were characterized by UV–Vis absorption spectroscopy, DSC, ¹H and ¹³C NMR, and cyclic voltammetry. Their optoelectronic properties were further investigated by DFT and TD-DFT calculations. Photocyclisation induced a marked bathochromic extension of the absorption profile, decreasing the optical band gap from 3.19 eV for the pyridinium precursor to 2.61 eV for the fused benzothienoquinolizinium salt. Cyclic voltammetry revealed a stabilized electrochemical LUMO level of approximately −3.87 eV, supporting the electron-deficient character of the nitro/cyano-substituted cationic scaffold. Frontier molecular orbital analysis showed that the HOMO and LUMO are mainly localized on the fused π-conjugated core and electron-withdrawing aryl substituents, with negligible contribution from the tetradecyl chain and BF₄⁻ counterion. TD-DFT and electron excitation analyses indicated that the monomeric low-energy transition has mixed local/charge-transfer character, whereas π-stacked dimers, especially the face-to-face arrangement, enhance charge transfer character and reduce electron–hole Coulombic attraction. Marcus type charge transport calculations revealed packing dependent behavior, with the face-to-face dimer displaying nearly ambipolar transport with a slight electron preference. A preliminary theoretical donor–acceptor model with hexaphenyl-substituted hexabenzocoronene further suggested energetic compatibility and strong intermolecular charge-transfer character. Overall, these results identify this benzothienoquinolizinium tetrafluoroborate as a promising electron-deficient cationic π-scaffold for future organic optoelectronic materials. Full article

(This article belongs to the Special Issue Advances in Optoelectronic Materials)

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19 pages, 7944 KB

Open AccessArticle

Multiphysics Analysis of Porous MWCNT Films with Tunable Thermo-Optical, Nonlinear Optical, and Magneto-Optical Responses

by José Antonio García-Merino

Crystals 2026, 16(9), 574; https://doi.org/10.3390/cryst16090574 - 2 Sep 2026

Abstract

Porous multi-walled carbon nanotube (MWCNT) films combine strong optical absorption with thermal, Kerr-like, thermo-optical, and magneto-optical responses. However, these effects depend on film structure and may require different design conditions. In this work, a multiphysics model was used to analyze 12 MWCNT film [...] Read more.

Porous multi-walled carbon nanotube (MWCNT) films combine strong optical absorption with thermal, Kerr-like, thermo-optical, and magneto-optical responses. However, these effects depend on film structure and may require different design conditions. In this work, a multiphysics model was used to analyze 12 MWCNT film configurations with dependance on thicknesses, porosity, and orientation parameters. The model included optical attenuation, transient heating, nonlinear refraction, thermo-optic modulation, magneto-optical response, and optical phase shift under irradiances of 7–20 MW cm⁻² and magnetic fields up to 1 T. Optical density ranged from approximately 0.4 to 2.8, while transmittance showed negligible variation with irradiance. Thin and porous films produced the highest temperature rises, approximately 4.5 K, and the largest total refractive-index changes. In contrast, thicker films generated larger accumulated phase shifts. The thermo-optic contribution is dominated under nanosecond laser irradiation. As the pulse duration approached the picosecond regime, the lower deposited energy reduced the photothermal response, so the Kerr-like and magneto-optical terms accounted for a larger total refractive-index change. This predictive parametric study identifies architecture- and pulse-dependent trends for future experimental evaluation of multifunctional MWCNT films. Full article

(This article belongs to the Special Issue Functional Thin Films: Growth, Characterization, and Applications)

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16 pages, 24138 KB

Open AccessArticle

An Approach for Defect Detection in Friction Stir Welding Based on the Welding Force and Machine Learning

by Ming Zeng, Jun Zhu and Wei Zhang

Crystals 2026, 16(9), 573; https://doi.org/10.3390/cryst16090573 - 2 Sep 2026

Abstract

This study leverages multiple machine learning algorithms for defect detection in friction stir welding (FSW), utilizing force-derived features as model inputs. Furthermore, the underlying relationships between welding forces and defect formation were systematically investigated, alongside an evaluation of the efficacy of force-feature-driven defect [...] Read more.

This study leverages multiple machine learning algorithms for defect detection in friction stir welding (FSW), utilizing force-derived features as model inputs. Furthermore, the underlying relationships between welding forces and defect formation were systematically investigated, alongside an evaluation of the efficacy of force-feature-driven defect detection models. Results indicated that the variations in the averages and waveforms in the traverse force (

F_{x}

), lateral force (

F_{y}

) and plunge force (

F_{z}

) are highly responsible for the defect formation in FSW joints, such that an increase in

F_{y}

causes waveform distortions in

F_{x}

and

F_{y}

.

F_{y a v g}

is the most important feature for the defect formation for 724 sets of experimental data. Defect detection based on thresholding of F_yavg and F_zavg achieves an accuracy of 80.3%. In contrast, four machine learning algorithms—Decision Tree (DT), K-Nearest Neighbors (KNNs), Support Vector Machine (SVM), and Artificial Neural Network (ANN)—were employed to construct defect detection models using the extracted force features as inputs, yielding accuracies of 93.5%, 97.5%, 95.7% and 94.9%, respectively. These findings further elucidate the underlying mechanics, that is, F_x and F_y primarily originated from the extrusion and shear forces induced by the probe’s rotation and traverse, whereas F_z was predominantly attributed to the compressive action of the shoulder. Full article

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

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