Crystals

12 pages, 7003 KB

Open AccessArticle

The Comparison of Microstructure, Phase Composition and Mechanical Properties of Inconel 625 Alloys Obtained by Wire Arc and Wire Electron Beam Additive Manufacturing

by Denis Gurianov, Sergey Fortuna, Sergei Tarasov, Vyacheslav Semenchuk, Nikolay Shamarin, Andrey Chumaevskii, Valery Rubtsov, Alexander M. Korsunsky and Evgeny Kolubaev

Crystals 2025, 15(10), 848; https://doi.org/10.3390/cryst15100848 (registering DOI) - 29 Sep 2025

Abstract

The present paper compares the microstructure and mechanical properties of Inconel 625 alloy samples produced by using wire-arc additive manufacturing (WAAM) and wire electron beam additive manufacturing (WEBAM). The obtained wall-shaped samples did not contain any macroscopic defects in the form of cracks, [...] Read more.

The present paper compares the microstructure and mechanical properties of Inconel 625 alloy samples produced by using wire-arc additive manufacturing (WAAM) and wire electron beam additive manufacturing (WEBAM). The obtained wall-shaped samples did not contain any macroscopic defects in the form of cracks, delaminations and geometry distortions. The WAAM-built “wall” exhibits finer dendritic structures (WAAM—10–16 μm; WEBAM—20–25 μm). Also, the WAAM-built one is characterized by the more homogeneous-sized distribution of microstructure components. In both cases, the material is represented by the γ-phase, with large precipitates of MC-type carbides in the interdendritic spaces. Additionally, the sample obtained using the WAAM contained aluminum oxide. It was found that the intrinsic periodic heat treatment is not sufficient for the formation of the γ″-phase, and it is necessary to perform a subsequent long-term aging. However, the overall mechanical properties of both samples show similar levels of yield stress and ultimate tensile strength, and demonstrate the same degree of anisotropy. Full article

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15 pages, 8832 KB

Open AccessArticle

Preparation of Iron-Based Metallic Powders by the Electroplasma Method

by Nurtoleu Magazov, Almasbek Maulit, German Berezutskiy and Arystanbek Kussainov

Crystals 2025, 15(10), 847; https://doi.org/10.3390/cryst15100847 (registering DOI) - 29 Sep 2025

Abstract

In this work, the production of iron-containing powders by the electroplasma dispersion method was investigated under various discharge regimes and in electrolytes of different natures (NaCl and Na₂CO₃). The influence of technological parameters on particle morphology, phase composition, and [...] Read more.

In this work, the production of iron-containing powders by the electroplasma dispersion method was investigated under various discharge regimes and in electrolytes of different natures (NaCl and Na₂CO₃). The influence of technological parameters on particle morphology, phase composition, and elemental content was analyzed using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), as well as laser particle size distribution analysis. It was found that the single-stage mode at 350 V in NaCl electrolyte led to the formation of predominantly irregularly shaped and fragmented particles, with a limited amount of spherical powders. The two-stage mode (350 V for 5 s followed by 250 V) in NaCl ensured a more stable formation of spherical particles with sizes of 60–80 μm; however, it was accompanied by intensive surface oxidation. The highest fraction of spherical powders was obtained in a Na₂CO₃ electrolyte under the two-stage mode, where homogeneous spheres with diameters of 20–75 μm and smooth surfaces were formed. According to EDS analysis, the powders consisted mainly of iron and oxygen, while in the samples synthesized in Na₂CO₃, the presence of sodium was detected, indicating the formation of mixed Na–Fe–O oxide phases. XRD confirmed the presence of a metallic α-Fe matrix along with oxide phases Fe₂O₃ and Fe₃O₄, while granulometric analysis (D50 ≈ 55 μm) revealed a relatively narrow particle size distribution. The obtained results demonstrate that variation in the discharge regime and electrolyte composition enables targeted control over the morphology and phase composition of the powders, making the electroplasma method a promising approach for producing metallic powders with tailored properties. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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16 pages, 1577 KB

Open AccessReview

Advances in Electro-Optical Devices Enabled by Waveguide-Based Thin-Film Lithium Niobate

by Jingsong Wang, Xun Lu, Di Qiao and Xingjuan Zhao

Crystals 2025, 15(10), 846; https://doi.org/10.3390/cryst15100846 (registering DOI) - 28 Sep 2025

Abstract

Lithium niobate (LN) materials have become a key platform for constructing core optoelectronic devices such as electro-optic (EO) modulators, optical frequency combs, and integrated optical waveguides, owing to their broad transparent window, mature waveguide processes, and excellent electro-optic effect. They demonstrate revolutionary application [...] Read more.

Lithium niobate (LN) materials have become a key platform for constructing core optoelectronic devices such as electro-optic (EO) modulators, optical frequency combs, and integrated optical waveguides, owing to their broad transparent window, mature waveguide processes, and excellent electro-optic effect. They demonstrate revolutionary application value in light source generation, signal transmission, and intensity modulation of optical communication systems, and are hailed as the “silicon of the photonics field,” attracting significant attention from both academia and industry. Especially with the commercialization of high-quality thin-film lithium niobate (TFLN) materials, the performance of thin-film optoelectronic devices based on waveguide structures has achieved leapfrog improvements, with their loss characteristics and modulation bandwidth far exceeding those of traditional bulk material devices. This paper systematically combs the photonic properties of LN materials, introduces in detail the electro-optic effect and electro-optic modulation principle of LN electro-optic modulators, reviews some recent research achievements of scholars, focuses on expounding the preparation processes of waveguide-based TFLN, the types of waveguide-based optoelectronic devices, and the research progress of these devices, and discusses and compares the advantages and development potential of different routes. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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22 pages, 9045 KB

Open AccessArticle

Weld Power, Heat Generation and Microstructure in FSW and SFSW of 11Cr-1.6W-1.6Ni Martensitic Stainless Steel: The Impact of Tool Rotation Rate

by Mohamed Ragab, Naser Alsaleh, Mohamed M. El-Sayed Seleman, Mohamed M. Z. Ahmed, Sabbah Ataya and Yousef G. Y. Elshaghoul

Crystals 2025, 15(10), 845; https://doi.org/10.3390/cryst15100845 (registering DOI) - 28 Sep 2025

Abstract

Friction stir welding (FSW) is a leading technique for joining high-strength steel. This study investigates the relationship between weld power, heat generation (HG), cooling medium, and parent austenite grain (PAG) size during both FSW and submerged FSW (SFSW) processes on 11Cr-1.6W-1.6Ni Martensitic Stainless [...] Read more.

Friction stir welding (FSW) is a leading technique for joining high-strength steel. This study investigates the relationship between weld power, heat generation (HG), cooling medium, and parent austenite grain (PAG) size during both FSW and submerged FSW (SFSW) processes on 11Cr-1.6W-1.6Ni Martensitic Stainless Steel. Weld power and HG were determined by measuring plunge force and tool torque at various tool rotation rates (350–550 rpm). Additionally, the PAG size and microstructural phases in the base metal (BM), thermo-mechanically affected zone (TMAZ), and stir zone (SZ) were examined using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD). The results indicated that the SFSW of martensitic steel required a plunge force twice that of the FSW process, along with greater weld power. The heat generated during SFSW was 130% higher than in FSW at 550 rpm. Despite this, the peak temperatures in the SZ were lower in SFSW as a result of the surrounding water’s high heat absorption. This difference in thermal behavior significantly affected the microstructure. While FSW resulted in a complete phase transformation to fine PAG, SFSW showed only minimal or partial transformation and a higher strain rate. Consequently, the SZ and TMAZ in SFSW exhibited a higher hardness than in FSW. Full article

(This article belongs to the Topic Microstructure and Properties in Metals and Alloys, 3rd Volume)

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27 pages, 4821 KB

Open AccessArticle

Experimental Investigation and Machine Learning Modeling of Electrical Discharge Machining Characteristics of AZ31/B₄C/GNP_s Hybrid Composites

by Dhanunjay Kumar Ammisetti, Satya Sai Harish Kruthiventi, Krishna Prakash Arunachalam, Victor Poblete Pulgar, Ravi Kumar Kottala, Seepana Praveenkumar and Pasupureddy Srinivasa Rao

Crystals 2025, 15(10), 844; https://doi.org/10.3390/cryst15100844 (registering DOI) - 27 Sep 2025

Abstract

Magnesium alloys, like AZ31, possess a desirable low weight and high specific strength, which make them favorable for aerospace and auto applications, yet their difficulty to machine limits their broader implementation for the industry. Electrical discharge machining (EDM) is an effective technology for [...] Read more.

Magnesium alloys, like AZ31, possess a desirable low weight and high specific strength, which make them favorable for aerospace and auto applications, yet their difficulty to machine limits their broader implementation for the industry. Electrical discharge machining (EDM) is an effective technology for machining difficult-to-machine materials, particularly when the materials are reinforced with ceramic and graphene-based fillers. This study examines the impact of reinforcement percentage (R) and different electrical discharge machining (EDM) parameters such as current (I), pulse on time (T_on) and pulse off time (T_off) on the material removal rate (MRR) and surface roughness (SR) of AZ31/B₄C/GNPs composites. The combined reinforcement range varies from 2 wt.% to 4 wt.%. The Taguchi design (L27) is utilized to conduct the experiments in this study. ANOVA of the experimental data indicated that current (I) significantly affects MRR and SR, exhibiting the greatest contribution of 44.93% and 51.39% on MRR and SR, respectively, among the variables analyzed. The surface integrity properties of EDMed surfaces are examined using SEM under both higher and lower material removal rate settings. Diverse machine learning techniques, including linear regression (LR), polynomial regression (PR), Random Forest (RF), and Gradient Boost Regression (GBR), are employed to construct an efficient predictive model for outcome estimation. The built models are trained and evaluated using 80% and 20% of the total data points, respectively. Statistical measures (MSE, RMSE, and R²) are utilized to evaluate the performance of the models. Among all the developed models, GBR exhibited superior performance in predicting MRR and SR, achieving high accuracy (exceeding 92%) and lower error rates compared to the other models evaluated in this work. This work demonstrated the synergy between techniques in optimizing EDM performance for hybrid composites using a statistical design and machine learning strategies that will facilitate greater use of hybrid composites in high-precision engineering applications and advanced manufacturing sectors. Full article

(This article belongs to the Special Issue Synthesis, Characterizations and Applications of Atomically Precise Nanomaterials)

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14 pages, 10266 KB

Open AccessArticle

Color Mechanism of Blue Myanmar Jadeite Jade: The Role of Trace Elements and Mineralogical Characteristics

by Shangzhan Dai, Yu Zhang, Guanghai Shi and Taafee Long

Crystals 2025, 15(10), 843; https://doi.org/10.3390/cryst15100843 (registering DOI) - 27 Sep 2025

Abstract

Myanmar blue jadeite jade is a rare and highly prized gemstone, yet its coloration and formative mechanisms remain poorly understood. In this study, petrographic analysis, ultraviolet–visible (UV–Vis) spectroscopy, electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were performed [...] Read more.

Myanmar blue jadeite jade is a rare and highly prized gemstone, yet its coloration and formative mechanisms remain poorly understood. In this study, petrographic analysis, ultraviolet–visible (UV–Vis) spectroscopy, electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were performed on a sample of Myanmar blue jadeite with small white blocks to investigate its mineral composition, trace element distribution, and coloration mechanisms. Most of the sample was found to be blue, with surrounding white areas occurring in small ball-shaped blocks. The main mineral component in both the blue and white domains was jadeite. Although both areas underwent recrystallization, their textures differed significantly. The blue areas retained primary structural features within a medium- to fine-grained texture, reflecting relatively weaker recrystallization. The white areas, however, were recrystallized into a micro-grained texture, reflecting relatively stronger recrystallization, with the superimposed effects of external stress producing a fragmented appearance. The blue jadeite had relatively higher contents of Ti, Fe, Ca, and Mg, while the white jadeite contained compositions close to those of near-end-member jadeite. It was noted that, while white jadeite may have a high Ti content, its Fe content is low. UV–Vis spectra showed a broad absorption band at 610 nm associated with Fe²⁺-Ti⁴⁺ charge transfer and a gradually increasing absorption band starting at 480 nm related to V⁴⁺. Combining the chemical composition and the characteristics of the UV–Vis spectra, we infer that the blue coloration of jadeite is attributed to Fe²⁺-Ti⁴⁺ charge transfer; i.e., the presence of both Ti and Fe in blue jadeite plays a key role in its color formation. V⁴⁺ exhibited no significant linear correlation with the development of blue coloration. Prominent oscillatory zoning was observed in the jadeite, transitioning from NaAlSi₂O₆-dominant cores to Ca-Mg-Fe-Ti-enriched rims, reflecting the trend of fluid evolution during blue jadeite crystallization. Petrographic analysis indicated that the formation of the Myanmar blue jadeite occurred in two or three stages, with the blue regions forming earlier than the white regions. The blue jadeite also underwent significant recrystallization. Our findings contribute to the understanding of the formation of blue jadeite and the diversity of colors in jadeite jade. Full article

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

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27 pages, 2219 KB

Open AccessArticle

Multiscale Theory of Dislocation Plasticity

by Alexander R. Umantsev

Crystals 2025, 15(10), 842; https://doi.org/10.3390/cryst15100842 (registering DOI) - 27 Sep 2025

Abstract

Motion of dislocations is a common mechanism of plasticity in many materials. Dislocation-mediated deformation is essentially an inhomogeneous process, which is manifest in the formation of slip lines and complicated cell wall structures. An adequate description of these processes is an important goal [...] Read more.

Motion of dislocations is a common mechanism of plasticity in many materials. Dislocation-mediated deformation is essentially an inhomogeneous process, which is manifest in the formation of slip lines and complicated cell wall structures. An adequate description of these processes is an important goal of Materials Theory, which aims to describe the mechanical properties of materials and their reliability in service. This publication advances the thermodynamically consistent theory of dislocation-mediated plasticity to include the spatial gradients of the independent variables. We conducted the renormalization group scaling analysis of deformation and obtained the low-energy dislocation structures as ordinary solutions of the equilibrium equations without any arbitrary assumptions. We matched the emerging theoretical structures with the experimentally observed and made several predictions regarding possible experiments. Full article

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13 pages, 2571 KB

Open AccessArticle

Operando NRVS on LiFePO₄ Battery with ⁵⁷Fe Phonon DOS

by Alexey Rulev, Nobumoto Nagasawa, Haobo Li, Hongxin Wang, Stephen P. Cramer, Qianli Chen, Yoshitaka Yoda and Artur Braun

Crystals 2025, 15(10), 841; https://doi.org/10.3390/cryst15100841 (registering DOI) - 27 Sep 2025

Abstract

The vibration properties of materials play a role in their conduction of electric charges. Ionic conductors such as electrodes and solid electrolytes are also relevant in this respect. The vibration properties are typically assessed with infrared and Raman spectroscopy, and inelastic neutron scattering, [...] Read more.

The vibration properties of materials play a role in their conduction of electric charges. Ionic conductors such as electrodes and solid electrolytes are also relevant in this respect. The vibration properties are typically assessed with infrared and Raman spectroscopy, and inelastic neutron scattering, which all allow for the derivation of the phonon density of states (PDOS) in part of a full portion of the Brioullin zone. Nuclear resonant vibration spectroscopy (NRVS) is a novel method that produces the element-specific PDOS from Mössbauer-active isotopes in a compound. We employed NRVS operando on a pouch cell battery containing a Li⁵⁷FePO₄ electrode, and thus could derive the PDOS of the ⁵⁷Fe in the electrode during charging and discharging. The spectra reveal reversible vibrational changes associated with the two-phase conversion between LiFePO₄ and FePO₄, as well as signatures of metastable intermediate states. We demonstrate how the NRVS data can be used to tune the atomistic simulations to accurately reconstruct the full vibration structures of the battery materials in operando conditions. Unlike optical techniques, NRVS provides bulk-sensitive, element-specific access to the full phonon spectrum under realistic operando conditions. These results establish NRVS as a powerful method to probe lattice dynamics in working batteries and to advance the understanding of ion transport and phase transformation mechanisms in electrode materials. Full article

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

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17 pages, 3150 KB

Open AccessArticle

Design of Near-UV Photoluminescent Liquid-Crystalline Dimers: Roles of Fluorinated Aromatic Ring Position and Flexible Linker

by Sorato Inui, Hayato Kitaoka, Yuto Eguchi, Motohiro Yasui, Tsutomu Konno and Shigeyuki Yamada

Crystals 2025, 15(10), 840; https://doi.org/10.3390/cryst15100840 (registering DOI) - 27 Sep 2025

Abstract

Near-ultraviolet photoluminescence liquid-crystalline molecules (PLLCs) have attracted attention for temperature-responsive photoluminescence (PL) modulation and ON/OFF sensing under external stimuli. We recently developed mesogenic dimers composed of two hexyloxy-substituted, fluorinated tolane-type cores linked by alkylene-1,n-dioxy chains that exhibited near-UV PL in the [...] Read more.

Near-ultraviolet photoluminescence liquid-crystalline molecules (PLLCs) have attracted attention for temperature-responsive photoluminescence (PL) modulation and ON/OFF sensing under external stimuli. We recently developed mesogenic dimers composed of two hexyloxy-substituted, fluorinated tolane-type cores linked by alkylene-1,n-dioxy chains that exhibited near-UV PL in the solid state. However, the formation of LC phases and the temperature range of the LC state were limited. To improve LC phase stability, in this study, we extended the flexible terminal chains and repositioned the fluorinated aromatic rings from the outer to the inner core positions. Accordingly, we synthesized mesogenic dimers with even-numbered alkylene-1,n-dioxy linkers (hexylene, octylene, and decylene) and outer- or inner-ring fluorination. Outer-ring fluorination led to high melting temperatures and stable crystalline phases with limited mesophase formation. In contrast, inner-ring fluorination induced nematic phases upon heating and cooling owing to zig-zag molecular structures that disrupted crystallinity. Photophysical studies confirmed near-UV PL in solution and solid states; however, the quantum yield of the solution PL was low (<0.01). In the solid state, the PL efficiencies and wavelengths were influenced by the fluorinated aromatic ring position and linker length. This study provides important molecular design criteria for developing stable LC materials with tunable near-UV luminescence for temperature-responsive optical devices. Full article

(This article belongs to the Special Issue State-of-the-Art Liquid Crystals Research in Japan (2nd Edition))

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22 pages, 5035 KB

Open AccessArticle

Effect of Small Deformations on Optimisation of Final Crystallographic Texture and Microstructure in Non-Oriented FeSi Steels

by Ivan Petrišinec, Marcela Motýľová, František Kováč, Ladislav Falat, Viktor Puchý, Mária Podobová and František Kromka

Crystals 2025, 15(10), 839; https://doi.org/10.3390/cryst15100839 - 26 Sep 2025

Abstract

Improving the isotropic magnetic properties of FeSi electrical steels has traditionally focused on enhancing their crystallographic texture and microstructural morphology. Strengthening the cube texture within a ferritic matrix of optimal grain size is known to reduce core losses and increase magnetic induction. However, [...] Read more.

Improving the isotropic magnetic properties of FeSi electrical steels has traditionally focused on enhancing their crystallographic texture and microstructural morphology. Strengthening the cube texture within a ferritic matrix of optimal grain size is known to reduce core losses and increase magnetic induction. However, conventional cold rolling followed by annealing remains insufficient to optimise the magnetic performance of thin FeSi strips fully. This study explores an alternative approach based on grain boundary migration driven by temperature gradients combined with deformation gradients, either across the sheet thickness or between neighbouring grains, in thin, weakly deformed non-oriented (NO) electrical steel sheets. The concept relies on deformation-induced grain growth supported by rapid heat transport to promote the preferential formation of coarse grains with favourable orientations. Experimental material consisted of vacuum-degassed FeSi steel with low silicon content. Controlled deformation was introduced by temper rolling at room temperature with 2–40% thickness reductions, followed by rapid recrystallisation annealing at 950 °C. Microstructure, texture, and residual strain distributions were analysed using inverse pole figure (IPF) maps, kernel average misorientation (KAM) maps, and orientation distribution function (ODF) sections derived from electron backscattered diffraction (EBSD) data. This combined thermomechanical treatment produced coarse-grained microstructures with an enhanced cube texture component, reducing coercivity from 162 A/m to 65 A/m. These results demonstrate that temper rolling combined with dynamic annealing can surpass the limitations of conventional processing routes for NO FeSi steels. Full article

(This article belongs to the Special Issue Microstructure and Deformation of Advanced Alloys (2nd Edition))

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14 pages, 3057 KB

Open AccessArticle

Microstructure and Compressive Properties of (Ti₅₁Zr₂₅Cu₆Be₁₈)_100−xV_x Bulk Metallic Glass Matrix Composites

by Xinhua Huang, Junnan Li, Guang Wang, Bin Chen, Chenghao Wei and Yuejun Ouyang

Crystals 2025, 15(10), 838; https://doi.org/10.3390/cryst15100838 - 26 Sep 2025

Abstract

Metallic glass alloys exhibit excellent properties, yet suffer from poor room-temperature plasticity, a limitation that restricts their engineering applications. Bulk metallic glass matrix composites (BMGMCs) have proven effective in enhancing the plasticity of metallic glasses, and the addition of alloying elements serves as [...] Read more.

Metallic glass alloys exhibit excellent properties, yet suffer from poor room-temperature plasticity, a limitation that restricts their engineering applications. Bulk metallic glass matrix composites (BMGMCs) have proven effective in enhancing the plasticity of metallic glasses, and the addition of alloying elements serves as a key strategy to regulate their microstructure and optimize the properties of these composites. This study aims to investigate the effects of a vanadium (V) addition on the mechanical properties and microstructure of Ti-based BMGMCs, while exploring the underlying mechanism of V’s influence. Using (Ti₅₁Zr₂₅Cu₆Be₁₈)_100−xV_x (x = 0, 4, 8, 12, 16, 20) BMGMCs as test specimens, microstructural characterization was performed via X-ray diffraction (XRD) and scanning electron microscopy (SEM), and compressive mechanical properties were tested. The results indicate that a V addition refines dendrites without altering the phase composition, which remains composed of β-Ti crystals and an amorphous matrix. With the increase in V content, the compressive plastic strain shows a trend of first increasing and then decreasing; when x = 12, the specimen exhibits the maximum compressive plastic strain, reaching 7.9%. Additionally, the volume fraction of the crystalline phase gradually increases with increasing V content. This study clarifies the mechanism by which V regulates the microstructure and properties of Ti-based BMGMCs, thereby providing theoretical and experimental insights for optimizing alloy compositions to enhance the mechanical performance. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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12 pages, 2759 KB

Open AccessArticle

Calcium Hexaboride Synthesis from Anhydrous Colemanite by Mechanochemical Method

by Aylin Yasemin and Ahmet F. Karabulut

Crystals 2025, 15(10), 837; https://doi.org/10.3390/cryst15100837 - 26 Sep 2025

Abstract

In this study, calcium hexaboride (CaB₆) was successfully synthesized from anhydrous colemanite (Ca₂B₆O₁₁) via a mechanochemical approach. The synthesis process was optimized in two stages: by adjusting the reaction time and varying the carbon-to-colemanite ratio. [...] Read more.

In this study, calcium hexaboride (CaB₆) was successfully synthesized from anhydrous colemanite (Ca₂B₆O₁₁) via a mechanochemical approach. The synthesis process was optimized in two stages: by adjusting the reaction time and varying the carbon-to-colemanite ratio. Structural and compositional analyses were performed using FT-IR, XRD, SEM, and EDX techniques. The optimal synthesis condition was found to be a carbon-to-colemanite ratio of 10:1 and a reaction time of 1020 min, yielding the highest Ca–B vibrational intensities in FT-IR spectra. The mechanochemical method enabled CaB₆ formation at ambient conditions without the need for high temperature or pressure, offering a significant advantage over traditional methods. The results suggest that this method can serve as a low-energy route for the synthesis of metal borides, which are promising candidates for applications in refractory materials, electronics, and hydrogen storage systems. Full article

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

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16 pages, 2101 KB

Open AccessArticle

Structure and Mechanical Properties of Tubular Steel Products Processed by Cold Rotary Swaging

by Dorin Luca, Ion-Adrian Sărbătoare, Corneliu Munteanu, Fabian-Cezar Lupu, Dorian D. Luca and Cătălin-Andrei Țugui

Crystals 2025, 15(10), 836; https://doi.org/10.3390/cryst15100836 - 26 Sep 2025

Abstract

Rotary swaging (RS) is applied for the manufacturing of bars, stepped shafts, tubes with complex internal profiles, bimetallic composites, and similar products. This process falls under the category of severe plastic deformation (SPD) methods, which produce ultrafine-grained materials that provide superior properties in [...] Read more.

Rotary swaging (RS) is applied for the manufacturing of bars, stepped shafts, tubes with complex internal profiles, bimetallic composites, and similar products. This process falls under the category of severe plastic deformation (SPD) methods, which produce ultrafine-grained materials that provide superior properties in service. Our study investigated the effect of cold RS on the structure, grain size, and microhardness of AISI 304 stainless steel and CK45 carbon steel. Tubular specimens were processed by RS with the purpose of obtaining conical parts with a closed end, achieving a maximum reduction of nearly 44%. Samples were taken by longitudinal sectioning along the diameter from three zones with different degrees of deformation and subjected to structural analysis using scanning electron microscopy (SEM). The investigations were complemented by microhardness measurements in the axial direction for samples of both steels. The resulting structures revealed material texturing and a continuous decrease in grain size with increasing swaging ratio. The average grain size was reduced by approximately 46% in AISI 304 steel and by around 50% in CK45 steel. The microhardness of the materials increased by about 179% for AISI 304 steel and by approximately 95% for CK45 steel. The obtained results are discussed, highlighting the effect of cold RS processing on the two steels studied. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Alloys and Composites)

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15 pages, 3254 KB

Open AccessArticle

Mono- and Polynuclear Hg(II) Complexes with Mixed Ligands: Nicotinamide and Oxalate, Nitrate, or Sulphate

by Laurențiu Pricop, Anamaria Hanganu, Mihaela Ganciarov and Augustin M. Mădălan

Crystals 2025, 15(10), 835; https://doi.org/10.3390/cryst15100835 - 25 Sep 2025

Abstract

Three new complexes of Hg(II), with the general formulas [Hg₂(ox)₂(NA)₄]_n·3nH₂O (1), [Hg(NO₃)₂(NA)₂(H₂O)₂]·2NA (2), and [Hg₂(SO₄)₂(H [...] Read more.

Three new complexes of Hg(II), with the general formulas [Hg₂(ox)₂(NA)₄]_n·3nH₂O (1), [Hg(NO₃)₂(NA)₂(H₂O)₂]·2NA (2), and [Hg₂(SO₄)₂(H₂O)₂(NA)₄]·6H₂O (3), where ox = oxalate and NA = nicotinamide, were synthesized and characterized by single crystal X-ray diffraction, elemental analysis, FT-IR, and fluorescence spectra. For complex (2), ¹³C and ¹H NMR spectra were recorded. Thermogravimetric analysis was also performed for complexes (1) and (2). Single crystal X-ray diffraction shows that in the polymeric complex (1) and the binuclear complex (3), the Hg(II) ions are hexacoordinated, whereas in the mononuclear complex (2), Hg(II) is octacoordinated. In complex (1), each oxalate group acts in a µ₄ coordination manner, the basal plan being made up by four oxygen atoms belonging to the two oxalate ligands, while the nicotinamide molecules occupy the axial positions. In complex (2), the nitrate groups coordinate in a bidentate chelating mode, whereas in complex (3), each sulphate ligand acts in a bidentate chelating–bis monodentate bridging manner. Full article

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

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17 pages, 2682 KB

Open AccessArticle

In-Plane Magnetic Field-Induced Multiple-Q Magnetic Phases in Frustrated Magnets with Easy-Plane and Bond-Dependent Anisotropy

by Satoru Hayami

Crystals 2025, 15(10), 834; https://doi.org/10.3390/cryst15100834 - 25 Sep 2025

Abstract

We numerically investigate instabilities toward bimeron crystals and multiple-Q magnetic states induced by an in-plane external magnetic field in centrosymmetric magnets with magnetic anisotropy. By focusing on the interplay between easy-plane single-ion anisotropy and bond-dependent anisotropy originating from relativistic spin–orbit coupling in [...] Read more.

We numerically investigate instabilities toward bimeron crystals and multiple-Q magnetic states induced by an in-plane external magnetic field in centrosymmetric magnets with magnetic anisotropy. By focusing on the interplay between easy-plane single-ion anisotropy and bond-dependent anisotropy originating from relativistic spin–orbit coupling in crystalline environments, we construct the magnetic phase diagram of an effective spin model with competing momentum-resolved interactions using simulated annealing. Our analysis reveals that the bimeron crystal is stabilized within the regime of weak bond-dependent anisotropy, independent of its sign, whereas increasing the strength of bond-dependent anisotropy drives the system into a topologically trivial triple-Q magnetic state. The obtained bimeron crystal is characterized by finite scalar spin chirality and triple-Q modulations in both the in-plane and out-of-plane spin components. These findings demonstrate that centrosymmetric easy-plane magnets provide a fertile platform for realizing nontrivial topological spin textures without relying on Dzyaloshinskii–Moriya interactions, thereby opening new avenues for inducing emergent topological transport phenomena in centrosymmetric materials. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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14 pages, 5885 KB

Open AccessArticle

Microvoids Enhance the Low-Cycle Fatigue Resistance of TiAl Alloys

by Hailiang Jin, Wenya Peng, Chunling Zhao, Zhilai Chen, Hao Ding, Wei Li and Junyan Zhou

Crystals 2025, 15(10), 833; https://doi.org/10.3390/cryst15100833 - 24 Sep 2025

Abstract

Voids have a crucial effect on the fatigue performance of materials. The general viewpoint is that voids, as possible sources of cracks, are harmful to the fatigue performance of materials. However, this study finds that microvoids enhance the low-cycle fatigue resistance of TiAl [...] Read more.

Voids have a crucial effect on the fatigue performance of materials. The general viewpoint is that voids, as possible sources of cracks, are harmful to the fatigue performance of materials. However, this study finds that microvoids enhance the low-cycle fatigue resistance of TiAl alloys, both in single crystal and polycrystal, using molecular dynamics simulations. Due to the difference between the simulation and test, the selected strain value is larger. It is found that during cyclic loading, Shockley partial dislocations preferentially nucleate around the microvoid in the single crystal, with stacking fault tetrahedra forming progressively to obstruct dislocation motion. The polycrystal model exhibits the synergistic effect of the microvoid–grain boundary, and the fatigue resistance is substantially enhanced through the combined mechanisms of Lomer–Cottrell lock formation, twin boundary migration, and phase transformation. In addition, simulation models with microvoids exhibit lower plastic strain energy density and enhance fatigue life compared to microvoid-free counterparts. The present study provides significant insights into designing γ-TiAl alloys through controlled microvoids to optimize fatigue resistance. Future work should include experimental validation to substantiate these computational findings. Full article

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

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21 pages, 4000 KB

Open AccessReview

Beyond Theoretical Limits: Extra Capacity in Conversion Reaction of Transition Metal Oxide Anodes for Lithium-Ion Batteries

by Mohammad Behzadnia, Rania Ramadan, Xuefeng Jiao, Ahmed M. Hashem and Likun Zhu

Crystals 2025, 15(10), 832; https://doi.org/10.3390/cryst15100832 - 24 Sep 2025

Abstract

Conversion-type transition metal oxides (TMOs) have emerged as promising anode materials for lithium-ion batteries (LIBs) owing to their high theoretical capacities and low cost. Intriguingly, many TMOs exhibit extra capacity that surpasses the limits predicted by conversion reaction mechanisms, challenging traditional electrochemical models [...] Read more.

Conversion-type transition metal oxides (TMOs) have emerged as promising anode materials for lithium-ion batteries (LIBs) owing to their high theoretical capacities and low cost. Intriguingly, many TMOs exhibit extra capacity that surpasses the limits predicted by conversion reaction mechanisms, challenging traditional electrochemical models and offering opportunities for next-generation high-energy storage. This review highlights the phenomenon of extra capacity in TMO anodes, emphasizing its mechanistic origins and practical implications. While these materials face well-known challenges such as low initial coulombic efficiency, solid electrolyte interphase (SEI) instability, and severe structural degradation due to large volume changes, they offer promising opportunities for achieving high energy density. Special emphasis is placed on understanding the underlying mechanisms that contribute to this anomalous capacity, including the role of reversible SEI formation, lithium-rich phases, reversible formation of LiOH, and interfacial storage phenomena. By clarifying these mechanisms and performance-enhancement approaches, this paper aims to guide future research toward the practical application of high-capacity conversion-type TMO anodes in next-generation LIBs. Full article

(This article belongs to the Special Issue Advances in Materials for Energy Conversion and Storage)

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16 pages, 813 KB

Open AccessArticle

Ferroaxial Property Under Hybrid Skyrmion Crystals

by Satoru Hayami

Crystals 2025, 15(10), 831; https://doi.org/10.3390/cryst15100831 - 24 Sep 2025

Abstract

The ferroaxial moment, a time-reversal-even axial dipole degree of freedom, plays a key role not only in conventional quantum states of matter but also in anomalous off-diagonal cross-correlated responses. Here, we theoretically demonstrate that a skyrmion crystal with a swirling non-coplanar spin texture [...] Read more.

The ferroaxial moment, a time-reversal-even axial dipole degree of freedom, plays a key role not only in conventional quantum states of matter but also in anomalous off-diagonal cross-correlated responses. Here, we theoretically demonstrate that a skyrmion crystal with a swirling non-coplanar spin texture can exhibit ferroaxiality. In particular, we show that a hybrid skyrmion crystal, formed by the superposition of Néel- and Bloch-type vortices, hosts a finite ferroaxial moment. The degree of ferroaxiality is quantified by calculating the expectation value of the electric toroidal dipole within a multi-orbital tight-binding model based on multipole representation theory. We further reveal characteristic off-diagonal responses associated with magnetic and magnetic toroidal multipoles under external magnetic fields. These results establish the hybrid skyrmion crystal as a promising platform for exploring the fundamental nature of ferroaxial moments. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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30 pages, 3236 KB

Open AccessReview

Recent Advancements in N-polar GaN HEMT Technology

by Emre Akso, Kamruzzaman Khan, Henry Collins, Boyu Wang, Robert Hamwey, Tanmay Chavan, Christopher Clymore, Weiyi Li, Oguz Odabasi, Matthew Guidry, Stacia Keller, Elaheh Ahmadi, Steven P. DenBaars and Umesh Mishra

Crystals 2025, 15(9), 830; https://doi.org/10.3390/cryst15090830 - 22 Sep 2025

Abstract

N-polar GaN HEMT technology has emerged as a disruptive technology that outperforms Ga-polar GaN HEMTs in terms of high-frequency power amplification capability. In this paper, the authors present a comprehensive review of the evolution of N-polar GaN HEMT technology from the perspective of [...] Read more.

N-polar GaN HEMT technology has emerged as a disruptive technology that outperforms Ga-polar GaN HEMTs in terms of high-frequency power amplification capability. In this paper, the authors present a comprehensive review of the evolution of N-polar GaN HEMT technology from the perspective of crystal growth, dielectrics, and metals on N-polar GaN, transistor design, and performance. Specifically, the authors discuss the progress of the N-polar GaN HEMTs toward high-frequency, high-power, and high-efficiency applications with recent record-level performances, demonstrated by the authors, at mmWave frequencies. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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