Crystals

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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17 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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23 pages, 985 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)

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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19 pages, 8252 KB

Open AccessArticle

Study on High-Temperature Fatigue Properties and Notch Sensitivity of Haynes 230 Alloy TIG-Welded Joints

by Lin Yang, Fuheng Nie, Guijun Mao, Jikun Yang, Tieshan Cao, Xingdong Chen and Xiaopeng Zhang

Crystals 2026, 16(9), 572; https://doi.org/10.3390/cryst16090572 - 2 Sep 2026

Abstract

This study investigates the high-temperature high-cycle-fatigue behavior of TIG-welded Haynes 230 alloy using smooth and notched specimens (Kt = 3) at 850–950 °C. Both elevated temperature and notch effect significantly degrade fatigue performance. As temperature increases, thermally activated crack initiation and propagation accelerate, [...] Read more.

This study investigates the high-temperature high-cycle-fatigue behavior of TIG-welded Haynes 230 alloy using smooth and notched specimens (Kt = 3) at 850–950 °C. Both elevated temperature and notch effect significantly degrade fatigue performance. As temperature increases, thermally activated crack initiation and propagation accelerate, shifting the S–N curves downward. Notched specimens exhibit substantially shorter fatigue lives due to stress concentration-induced multi-source crack initiation, dispersed propagation zones, and fragmented sudden fracture zones. The alloy shows low notch sensitivity across the test temperature range, with the lowest value at 900 °C. A unified fatigue life prediction model is established using a temperature correction factor exp[P × ()], demonstrating high fitting accuracy. M-G curves of notched specimens shift downward and leftward, revealing the aggravating effect of the notch on creep–fatigue interaction. Fractographic analysis shows that with increasing temperature, smooth specimens exhibit expanded sudden fracture zones and degraded striations, while notched specimens display multi-source initiation and a composite morphology of striations with fine dimples, consistent with macroscopic mechanical behavior. This work delivers comparative experimental data and mechanism-oriented insights for TIG-welded Haynes 230 joints within 850–950 °C; the proposed temperature-corrected model is valid for the investigated test window and provides reference for component performance analysis. Full article

(This article belongs to the Special Issue Alloys in Additive Manufacturing and Welding: Microstructure and Properties)

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13 pages, 19076 KB

Open AccessArticle

Advancing Bulk Growth of 100 mm AlN by Physical Vapor Transport

by Robert T. Bondokov, Shogen Matsumoto, Connor G. Carr, Kasey Hogan, Griffin Q. Norbury, Masato Kobayashi and James Grandusky

Crystals 2026, 16(9), 571; https://doi.org/10.3390/cryst16090571 - 2 Sep 2026

Abstract

Ultrawide bandgap (UWBG) semiconductors are destined to become the foundation for next-generation power and radio-frequency (RF) electronic devices. Their superior qualities such as high thermal conductivity, strong critical electric field, and robust mechanical and radiation hardness are driving continuous and widespread research. Amongst [...] Read more.

Ultrawide bandgap (UWBG) semiconductors are destined to become the foundation for next-generation power and radio-frequency (RF) electronic devices. Their superior qualities such as high thermal conductivity, strong critical electric field, and robust mechanical and radiation hardness are driving continuous and widespread research. Amongst the UWBG materials, aluminum nitride (AlN) is highly attractive due to its direct ultrawide bandgap of about 6.2 eV, resulting in one of the highest Baliga’s and Johnson’s figures of merit. Equally important as its properties are material availability and growth methods capable of producing large-diameter substrates. In this work we report on bulk growth of 100 mm AlN crystals using the physical vapor transport (PVT) technique. The thermal gradients were simulated and tailored to obtain adequate thermal stresses, resulting in substrates with narrow X-ray rocking curves and dislocation densities in the range of 10²–10⁵ cm⁻². In addition, the room-temperature thermal conductivity measured in two directions, perpendicular and parallel to the c-axis, was confirmed to be 300 W m⁻¹ K⁻¹. AlN substrates also demonstrated high UV transparency with absorption coefficients as low as 10 cm⁻¹ at 265 nm wavelength. These results, along with the availability of 100 mm substrates, demonstrate that AlN is ready for further exploration and development for the power and RF electronics industry. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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17 pages, 9401 KB

Open AccessArticle

Effects of Red Mud Particles and Oxides on the Microstructure and High-Temperature Tensile Properties of ZL109 Aluminum Alloy

by Anmin Li, Xia He, Zhuofang Huang, Zhi Wang, Yixin Yuan, Yushi Gong and Chunrong Chen

Crystals 2026, 16(9), 570; https://doi.org/10.3390/cryst16090570 - 1 Sep 2026

Abstract

Nickel coatings were deposited onto the surfaces of red mud, Al₂O₃, and Fe₂O₃ particles via an electroless plating technique. The nickel-coated particles (1.5 wt.%) were subsequently incorporated into a ZL109 aluminum alloy matrix to fabricate three [...] Read more.

Nickel coatings were deposited onto the surfaces of red mud, Al₂O₃, and Fe₂O₃ particles via an electroless plating technique. The nickel-coated particles (1.5 wt.%) were subsequently incorporated into a ZL109 aluminum alloy matrix to fabricate three types of composites using a stir-casting process, followed by a T6 heat treatment consisting of solution treatment at 515 °C for 8 h, water-bath quenching at 90–100 °C, and artificial aging at 175 °C for 12 h. The microstructural morphology and phase identification were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Furthermore, the high-temperature tensile properties of the fabricated alloys were evaluated at 350 °C and 400 °C. The results showed that the addition of 1.5 wt.% nickel-coated red mud led to a more uniform distribution of eutectic silicon and an increase in the content of the Al₅Cu₂Mg₈Si₆, Al₇Cu₄Ni, and Al₂Cu strengthening phases. These microstructural changes significantly enhanced the high-temperature tensile performance of the alloy. At 350 °C and 400 °C, the alloy reinforced with 1.5 wt.% nickel-coated red mud achieved tensile strengths of 97.8 MPa and 86.2 MPa, respectively. The combination of an appropriate amount of nickel-coated red mud and a suitable heat treatment process effectively improves the high-temperature stability and tensile properties of the ZL109 aluminum alloy, which could be attributed to the synergistic strengthening effect arising from the precipitation of high-temperature stable phases and the Orowan mechanism. Full article

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

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12 pages, 2407 KB

Open AccessArticle

Molecular Dynamics Simulation of Simultaneous High-Speed Impact of Double Tungsten Fragments on a Titanium Target Plate

by Meng Xiang, Xianjun Shi and Ruochen Sun

Crystals 2026, 16(9), 569; https://doi.org/10.3390/cryst16090569 - 31 Aug 2026

Abstract

This study employs molecular dynamics (MD) simulations to explore the high-speed impact behavior of double conical tungsten (W) fragments on titanium (Ti) target plates, focusing on fragment cloud formation, Ti damage evolution, and the effects of temperature and impact velocity. High-speed impact converts [...] Read more.

This study employs molecular dynamics (MD) simulations to explore the high-speed impact behavior of double conical tungsten (W) fragments on titanium (Ti) target plates, focusing on fragment cloud formation, Ti damage evolution, and the effects of temperature and impact velocity. High-speed impact converts W fragments’ kinetic energy into internal energy, causing W fragmentation and the formation of a mixed-phase fragment cloud, which induces severe damage to the Ti target. Under double-particle impacts, W fragments penetrate the Ti target to form a multi-source fragment cloud, with Ti target damage (characterized by amorphous phase distribution) undergoing initiation and extension stages. Higher temperatures broaden the high-temperature damage zone and increase crater size but do not change the impact penetration evolution mode or penetration depth. Impact velocity determines damage modes: low velocity causes non-through internal damage with a rear bulge, while high velocity leads to full perforation with mixed W-Ti fragment ejection, and lateral crater size is almost unaffected by velocity. This study innovatively reveals the atomic-scale damage evolution mechanism of Ti targets under dual conical W fragment impact, which fills the research gap in conventional single-fragment impact studies. These findings clarify the high-speed impact mechanism of Ti alloys, providing theoretical support for the design of Ti-based protective structures in engineering. Full article

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

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11 pages, 4196 KB

Open AccessArticle

Orientation-Dependent Compressibility of Tin Under High Pressure

by Na Yeong Ko

Crystals 2026, 16(9), 568; https://doi.org/10.3390/cryst16090568 - 30 Aug 2026

Abstract

This study investigates the effect of initial microstructure on the high-pressure mechanical properties of high-purity tin (Sn). Two Sn samples from the same commercial product were measured using high-pressure X-ray diffraction in diamond anvil cells. At ambient pressure, the two samples exhibited different [...] Read more.

This study investigates the effect of initial microstructure on the high-pressure mechanical properties of high-purity tin (Sn). Two Sn samples from the same commercial product were measured using high-pressure X-ray diffraction in diamond anvil cells. At ambient pressure, the two samples exhibited different initial crystallographic orientations; one showed random orientation, while the other exhibited preferred orientation (i.e., texture). In the low-pressure β-Sn phase, both samples exhibited the same bulk moduli with

B_{0}

= 55.0 ± 0.4 and 55.0 ± 2.3 GPa, respectively. However, their compressional behavior diverged significantly after the phase transition from β-Sn to the body-centered tetragonal (BCT) phase. The measured bulk moduli for the BCT phase were 60.0 ± 0.9 GPa for the randomly oriented Sn and 91.3 ± 1.4 GPa for the textured one. These results indicate that the initial microstructure can significantly influence the compressional response of Sn under high pressure. Full article

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

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16 pages, 22105 KB

Open AccessArticle

Effect of Tempering Temperature on Microstructure and Mechanical Properties of D406A Steel

by Ziyuan Xu, Fu Xiao and Yuanbiao Tan

Crystals 2026, 16(9), 567; https://doi.org/10.3390/cryst16090567 - 30 Aug 2026

Abstract

D406A steel serves as a critical structural material for load-bearing components in aerospace solid rocket motors. To achieve an excellent strength-plasticity balance of D406A steel in this work, the quenched specimens austenitized at 890 °C were subjected to tempering treatments at 320 °C, [...] Read more.

D406A steel serves as a critical structural material for load-bearing components in aerospace solid rocket motors. To achieve an excellent strength-plasticity balance of D406A steel in this work, the quenched specimens austenitized at 890 °C were subjected to tempering treatments at 320 °C, 350 °C, 380 °C and 410 °C, respectively. SEM and EBSD characterization were adopted to systematically investigate the effects of tempering temperature on the microstructure, grain boundary characteristics, local strain, Schmid factor and mechanical properties. The results reveal that the lath martensite gradually undergoes recovery and disintegration with increasing tempering temperature, while the fraction of low-angle grain boundaries rises first and then falls, reaching the maximum value of 48.2% for the specimen tempered at 350 °C. At this tempering temperature, the KAM distribution is uniform, the Schmid factors shift toward the medium-to-high range, the proportion of grains with soft orientation increases, and the deformation coordination capacity is optimal. The specimen tempered at 350 °C exhibits an ultimate tensile strength of 1633.9 MPa, a yield strength of 1262.5 MPa and a Vickers hardness of 485.4 HV, achieving the optimal synergy between strength and plasticity. Full article

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

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9 pages, 3179 KB

Open AccessArticle

Stability and Mechanical Properties for Al3-xCuxSc (x = 0–3) Compounds

by Tong-Hui Yao and Wenqiang Sun

Crystals 2026, 16(9), 566; https://doi.org/10.3390/cryst16090566 - 30 Aug 2026

Abstract

Recent research has shown that Cu atoms can incorporate into the L1₂₋Al₃Sc precipitates in Al-Cu-Sc alloys, forming Al_3−xCu_xSc compounds that serve as effective hydrogen traps. Nevertheless, the Cu-induced modifications to the stability and mechanical properties [...] Read more.

Recent research has shown that Cu atoms can incorporate into the L1₂₋Al₃Sc precipitates in Al-Cu-Sc alloys, forming Al_3−xCu_xSc compounds that serve as effective hydrogen traps. Nevertheless, the Cu-induced modifications to the stability and mechanical properties of these precipitates have not yet been systematically quantified. In this work, first-principles calculations are performed to systematically investigate the crystal structures, phase stability, elastic properties, and thermodynamic behavior of Al_3−xCu_xSc (x = 0, 1, 2, 3) compounds. Structural optimizations are carried out for all compositions, and the formation enthalpies, elastic constants, polycrystalline moduli, and Debye temperatures are derived from the computed total energies and stress–strain relationships. The calculations reveal that Al₂CuSc and AlCu₂Sc adopt tetragonal structures rather than the cubic L1₂-type symmetry found in Al₃Sc and Cu₃Sc, indicating a composition-driven structural transition. The formation enthalpy becomes progressively less negative with increasing Cu content, implying a reduction in thermodynamic driving force for compound formation. The computed elastic properties further show that Cu substitution decreases the bulk-to-shear modulus ratio and the Vickers hardness, while simultaneously enhancing the ductility of the material. Additionally, the Debye temperature exhibits a monotonic and rapid decrease from Al₃Sc to Cu₃Sc, reflecting a significant softening of the lattice vibrational spectra upon Cu alloying. These quantitative theoretical results provide a comprehensive basis for understanding the compositional dependence of the mechanical and thermal responses of Cu-modified Al₃Sc precipitates. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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13 pages, 6356 KB

Open AccessArticle

Structure and Photophysical Properties of a Cyclometalated Iridium(III) Complex with 5,6,7,8-Tetraphenyl-1,12-Diazatripheneylene Ligand

by Natsumi Yano, Ko Ikeda, Makoto Handa and Yusuke Kataoka

Crystals 2026, 16(9), 565; https://doi.org/10.3390/cryst16090565 - 29 Aug 2026

Abstract

A cyclometalated iridium(III) complex [Ir(ppy)₂(tpdp)]PF₆ ([1]PF₆; ppy = 2-phenylpyridinate, tpdp = 5,6,7,8-tetraphenyl-1,12-diazatripheneylene) was synthesized and structurally characterized by single-crystal X-ray diffraction analysis. In [1]⁺, two nitrogen atoms of tpdp coordinate to the iridium(III) ion with [...] Read more.

A cyclometalated iridium(III) complex [Ir(ppy)₂(tpdp)]PF₆ ([1]PF₆; ppy = 2-phenylpyridinate, tpdp = 5,6,7,8-tetraphenyl-1,12-diazatripheneylene) was synthesized and structurally characterized by single-crystal X-ray diffraction analysis. In [1]⁺, two nitrogen atoms of tpdp coordinate to the iridium(III) ion with Ir-N distances of 2.131(4) and 2.114(4) Å. The peripheral phenyl substituents of tpdp are oriented nearly perpendicular to the enlarged π-conjugated plane of tpdp. [1]PF₆ exhibits shoulder bands at 472, 407, 368, and 337 nm, while the absorption increases continuously from ca. 520 nm toward shorter wavelengths. This spectral feature is similar to that of [Ir(ppy)₂(phen)]PF₆ ([2]PF₆), but the absorption intensity is much higher for [1]PF₆ in the UV region. The contribution from the π–π* transition of the tpdp ligand was considered to be the reason that [1]PF₆ exhibits such strong absorption in the UV region. Furthermore, [1]PF₆ exhibits an emission from ³MLLCT at 558 nm, whereas [2]PF₆ exhibits it at 560 nm. The luminescence lifetime (τ) of [1]PF₆ was 411 ns, shorter than that of [2]PF₆ (900 ns), and the absolute quantum yield (Φ) of [1]PF₆ was 4.8%, lower than that of [2]PF₆ (20.5%). Cyclic voltammetry (CV) analysis in degassed CH₃CN revealed redox waves both at the negative and positive sides (E_1/2 = 1.28 and −1.38 V vs. SCE) for [1]PF₆. In addition, DFT calculations were performed to discuss the electronic structures and photophysical properties of [1]⁺. Full article

(This article belongs to the Special Issue Metal Coordination Complexes for Optical and Chiro-Optical Applications)

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20 pages, 18271 KB

Open AccessArticle

Influence of Nonuniform Anchoring on Defect Structures in Hemispherical Nematic Liquid Crystal Droplets

by Zhongqi Chen, Minghui Li, Liya Zhao, Yuqi Zhang, Jiazuo Meng, Hongxing Wu, Haoni Ma, Hui Zhang and Guili Zheng

Crystals 2026, 16(9), 564; https://doi.org/10.3390/cryst16090564 - 28 Aug 2026

Abstract

With continuing advances in interfacial sensing and tunable micro-optics, the potential applications of hemispherical nematic droplets in these fields have received increasing attention. Local variations in surface anchoring can modify their director configurations and thereby produce distinct optical responses. However, the specific manner [...] Read more.

With continuing advances in interfacial sensing and tunable micro-optics, the potential applications of hemispherical nematic droplets in these fields have received increasing attention. Local variations in surface anchoring can modify their director configurations and thereby produce distinct optical responses. However, the specific manner in which anchoring conditions govern director configurations and defect formation remains poorly understood. Using the Landau–de Gennes theory, we investigate a model of a hemispherical droplet bounded by a curved surface and a planar base, with homeotropic easy-axis orientations prescribed at both interfaces. Four anchoring scenarios are compared: uniform anchoring, continuously varying curved-surface anchoring, localized weak-anchoring bands placed at different positions, and combinations of curved-surface and planar-base anchoring strengths. The results show that droplet size, spherical-cap height, and the strength and spatial position of anchoring all affect the director defect formation. Reducing the curved-surface anchoring strength near the contact line allows the director field to vary more continuously in this region, thereby suppressing the formation of the ring-shaped defect-core region. Distinct configurations, including a split-core structure near the symmetry axis, are obtained when the planar-base anchoring strength is varied under strong curved-surface anchoring. Full article

(This article belongs to the Section Liquid Crystals)

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16 pages, 5814 KB

Open AccessArticle

Crystal, Optical, Thermal and Dielectric Properties, XPS, and NEXAFS of Magnesium-Doped Nickel–Bismuth Stibate Pyrochlore

by Nadezhda A. Zhuk, Maria G. Krzhizhanovskaya, Alexandra V. Koroleva, Shamil S. Shayakhmedov, Nikolay A. Sekushin, Vladimir A. Belyy, Olga V. Petrova, Sergey V. Nekipelov and Ratibor G. Chumakov

Crystals 2026, 16(9), 563; https://doi.org/10.3390/cryst16090563 - 28 Aug 2026

Abstract

The article presents the results of a study of the properties of a new pyrochlore (Bi_2.7Mg_0.46Ni_0.70Sb₂O_10+Δ) using X-ray powder diffraction analysis, high-temperature X-ray powder diffraction and thermal analysis, diffuse reflectance spectroscopy, impedance spectroscopy, [...] Read more.

The article presents the results of a study of the properties of a new pyrochlore (Bi_2.7Mg_0.46Ni_0.70Sb₂O_10+Δ) using X-ray powder diffraction analysis, high-temperature X-ray powder diffraction and thermal analysis, diffuse reflectance spectroscopy, impedance spectroscopy, and X-ray spectroscopy methods (XPS, NEXAFS). The Ni/Mg codoped bismuth stibate pyrochlore was synthesized using the solid-phase method. The best results of the Rietveld structure refinement were achieved for the disordered pyrochlore model (sp. gr. Fd-3m:2, a = 10.47574(6) Å). The results of modeling the cation distribution over crystallographic positions are presented. The thermal expansion coefficient (TEC) of pyrochlore increases monotonically from 6.8 × 10⁻⁶ °C⁻¹ (30 °C) to 9.8 × 10⁻⁶ °C⁻¹ (810 °C). Above 1080 °C, thermal dissociation of pyrochlore occurs with the formation of (Mg/Ni)Sb₂O₆ and two cubic phases. At temperatures below 200 °C, the sample exhibits primarily capacitive impedance. The sample capacitance (~17 pF) is independent of temperature and frequency up to 200 °C. The high-frequency relative permittivity and dielectric loss tangent are 30.5 and 5 × 10⁻⁴ (24 °C, 5 × 10⁴ Hz). The activation energy for conductivity is 0.99 eV. The analysis of NEXAFS and XPS spectra allowed for the determination of the charge state of the metal cations: Bi + (3-δ), Sb + (5-δ), Ni/Mg + 2. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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11 pages, 1728 KB

Open AccessArticle

Polymorphism vs. Aromaticity in Cathinone Derivative 2-Amino-1-(4-Bromo-2,5-Dimethoxyphenyl)Ethan-1-One (bk-2C-B)

by Natalina Makieieva, Teobald Kupka and Krzysztof Ejsmont

Crystals 2026, 16(9), 562; https://doi.org/10.3390/cryst16090562 - 28 Aug 2026

Abstract

Cathinone and its synthetic derivatives are one of the most commonly used narcotics in the world. Some studies describe their antidepressant and smoking cessation potential, as well as cytostatic activity on several cancer cell lines. The literature presents a limited amount of data [...] Read more.

Cathinone and its synthetic derivatives are one of the most commonly used narcotics in the world. Some studies describe their antidepressant and smoking cessation potential, as well as cytostatic activity on several cancer cell lines. The literature presents a limited amount of data on the polymorphism in cathinones crystals, as well as on the correlation between aromaticity and crystal stability. This work aims to analyze the effect of the crystal structure on the nucleus-independent chemical shift (NICS) and the harmonic oscillator model of aromaticity (HOMA) values of bk-2C-B cathinone derivative polymorphs—EBIJOR and EBIJUX. A comparative analysis of NICS and HOMA values with an isolated drug molecules is also performed in this study. A higher aromaticity of molecules in polymorph EBIJOR was observed, compared to in EBIJUX. This may indicate a higher stability of EBIJOR compared to EBIJUX. Full article

(This article belongs to the Special Issue Polymorphism and Phase Transitions in Crystal Materials)

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14 pages, 3965 KB

Open AccessArticle

Microstructure and Performance of Al₂O₃-Reinforced Copper Matrix Composites Prepared by Oscillatory Hot-Pressing Sintering

by Dongxiao Hong, Manyu Hua, Li Wang, Xixi Ji, Pengfei Wu, Jian Liu, Binggong Yan, Zhihai Cai, Yejun Li and Yonggang Tong

Crystals 2026, 16(9), 561; https://doi.org/10.3390/cryst16090561 - 28 Aug 2026

Abstract

In order to enhance the strength and wear resistance of pure copper without obvious sacrifice of high electrical conductivity, Al₂O₃ particle-reinforced copper matrix composites with different volume fractions of Al₂O₃ were fabricated via the oscillatory hot-pressing sintering [...] Read more.

In order to enhance the strength and wear resistance of pure copper without obvious sacrifice of high electrical conductivity, Al₂O₃ particle-reinforced copper matrix composites with different volume fractions of Al₂O₃ were fabricated via the oscillatory hot-pressing sintering process. The effects of Al₂O₃ content on the densification, microstructure, mechanical properties, electrical conductivity, and wear behaviors of the composites were systematically investigated. The results showed that oscillatory pressure effectively inhibited pore formation, and Al₂O₃ particles were uniformly distributed within the copper matrix. With the increase in the Al₂O₃ volume fraction, the densification of the composites decreased slightly, while the hardness, compressive strength and wear resistance were continuously improved. By contrast, the electrical conductivity declined marginally and the friction coefficient rose. The 10 vol.% Cu-Al₂O₃ composite exhibited the optimal comprehensive wear resistance, with a hardness of 123 HV and an electrical conductivity maintained at 80.2% IACS. The wear mode of the composites gradually shifts from single adhesive wear of pure copper to the combined effect of abrasive wear and oxidative wear. Full article

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

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17 pages, 4905 KB

Open AccessArticle

High Bit Rate and Compact All-Optical 4-to-2 Encoder Utilizing Nonlinear Resonant Cavities in Photonic Crystal Structure

by Aya Emad Alhussaini, Mohammed Dheyaa Saad, Mohanad Adil Hussein, Mohammad Javad Maleki and Mohammad Soroosh

Crystals 2026, 16(9), 560; https://doi.org/10.3390/cryst16090560 - 28 Aug 2026

Abstract

In this work, a novel all-optical 4-to-2 encoder employing nonlinear resonant cavities in a two-dimensional photonic crystal is proposed and numerically investigated. The encoder consists of a lattice of chalcogenide rods incorporating nonlinear Kerr-effect cavities, enabling selective wavelength coupling through intensity-controlled resonance. By [...] Read more.

In this work, a novel all-optical 4-to-2 encoder employing nonlinear resonant cavities in a two-dimensional photonic crystal is proposed and numerically investigated. The encoder consists of a lattice of chalcogenide rods incorporating nonlinear Kerr-effect cavities, enabling selective wavelength coupling through intensity-controlled resonance. By assigning three distinct optical input power levels, the proposed architecture successfully realizes all encoding states without requiring additional control signals or complex resonator configurations. Numerical results demonstrate correct encoding functionality with normalized logic-1 output powers ranging from 0.89 to 1.71 and logic-0 levels below 0.013, yielding a high contrast ratio of 18.35 dB. The encoder exhibits ultrafast temporal performance with a maximum rise time of only 108 fs, corresponding to a data transmission capability of 4.63 Tbit/s, while maintaining a low insertion loss of 3.73 dB. Furthermore, the proposed structure occupies an ultra-compact footprint of only 95 μm², outperforming previously reported photonic crystal encoders in terms of integration density and speed. With regard to its compactness, high switching speed, excellent signal discrimination, and compatibility with current nanofabrication technologies, the proposed encoder represents a promising building block for future photonic integrated circuits, optical computing systems, and high-capacity optical communication networks. Full article

(This article belongs to the Section Crystal Engineering)

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29 pages, 8840 KB

Open AccessReview

A Review of Fatigue Performance Research on Aluminum Alloy Forming, Heat Treatment, Additive Manufacturing and Surface Modification Technologies

by Baicheng Liu, Hongliang Zhang, Shenghan Li, Yurii Luhovskyi and Zhisheng Nong

Crystals 2026, 16(9), 559; https://doi.org/10.3390/cryst16090559 - 27 Aug 2026

Abstract

Aluminum alloy is a lightweight, high-strength material based on aluminum matrix with the addition of elements such as copper, magnesium, silicon, zinc, manganese, or lithium. Featuring low density, high specific strength, excellent formability, and outstanding corrosion resistance, it is widely applied in the [...] Read more.

Aluminum alloy is a lightweight, high-strength material based on aluminum matrix with the addition of elements such as copper, magnesium, silicon, zinc, manganese, or lithium. Featuring low density, high specific strength, excellent formability, and outstanding corrosion resistance, it is widely applied in the fields of aerospace, rail transit, automotive lightweighting, and additive manufacturing. In the aerospace sector, fatigue failure constitutes the primary failure mode of load-bearing components. This paper reviews the influence mechanisms of various strengthening technologies, namely shot peening (SP), laser shock processing (LSP), physical vapor deposition (PVD), micro-arc oxidation (MAO), anodic oxidation (ANO), additive manufacturing, casting, extrusion, and heat treatment, on the fatigue properties of aluminum alloys; analyzes the regulatory effects of process principles, coating compositions, and microstructures (grains, phase composition, and interfacial bonding) on crack initiation and propagation; discusses the synergistic effect between plastic deformation strengthening and coating functionality; summarizes the key material and process factors affecting the fatigue life of aluminum alloys; and finally prospects the technical development trends driven by high-reliability service requirements. Full article

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