Crystals

11 pages, 7570 KiB

Open AccessArticle

Enhancing the Energy Storage Properties and Breakdown Strength of Lead-Free Bismuth-Sodium Titanate-Based Ceramics Through NaNbO₃ Doping

by Jingxia Gao, Haizhou Guo, Hongxia Li, Hui Li, Liqin Yue, Rui Wang, Jiangyan Si, Qiaoqiao Zhao and Yangyang Zhang

Crystals 2025, 15(3), 287; https://doi.org/10.3390/cryst15030287 - 20 Mar 2025

Viewed by 302

Abstract

Dielectric capacitors with a high density of recoverable energy storage are extremely desirable for a variety of uses. However, these capacitors often exhibit lower breakdown strengths and energy efficiency compared to other materials, which poses significant challenges for their practical use. We report [...] Read more.

Dielectric capacitors with a high density of recoverable energy storage are extremely desirable for a variety of uses. However, these capacitors often exhibit lower breakdown strengths and energy efficiency compared to other materials, which poses significant challenges for their practical use. We report on a novel antiferroelectric ceramic system in the present study, (1 − x){0.97[0.985(0.93Bi_0.5Na_0.5TiO₃–0.07BaTiO₃)–0.015Er)]–0.03AlN}–xNaNbO₃ (x = 0, 10 wt%, 20 wt%, 30 wt%, and 40 wt%), synthesized via a conventional solid-state reaction approach. Here, (Bi_0.5Na_0.5TiO₃–BaTiO₃) is denoted as BNT–BT. We observed that varying the NaNbO₃ (NN) content gradually refined the grain size of the ceramics, narrowed their hysteresis loops, and transformed their phase structure from antiferroelectric to relaxor ferroelectric. These changes enhanced breakdown strength (E_b), thus increasing the performance of energy storage. Specifically, the recoverable energy density (W_rec) and energy storage efficiency (η), respectively, reached 0.67–1.06 J/cm³ and 44–88% at electric fields of 110–155 kV/cm, with the highest performance observed at 30 wt% NN doping. Additionally, over a broad range of temperature and frequency, the 70 wt% {0.97[0.985(BNT–BT)–0.015Er]–0.03AlN}–30 wt% NN ceramic demonstrated exceptional stability in energy storage. These results demonstrate the significant potential of lead-free(1 − x)({0.97[0.985(BNT–BT)–0.015Er]–0.03AlN}–xNN ceramics for the applications of high-performance energy storage. Full article

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

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37 pages, 19027 KiB

Open AccessArticle

The Diversity of Crystals, Microstructures and Texture That Form Ostreoidea Shells

by Anna Sancho Vaquer, Erika Griesshaber, Carmen Salas, Elizabeth M. Harper, Antonio G. Checa and Wolfgang W. Schmahl

Crystals 2025, 15(3), 286; https://doi.org/10.3390/cryst15030286 - 20 Mar 2025

Cited by 1 | Viewed by 193

Abstract

The shells of bivalved molluscs comprise, in general, few microstructures and very few textures. In the case of ostreoid oysters, a high diversity has been observed. The shells consist of columnar-prismatic, foliated, granular calcite and myostracal-prismatic aragonite. Furthermore, voids are incorporated into the [...] Read more.

The shells of bivalved molluscs comprise, in general, few microstructures and very few textures. In the case of ostreoid oysters, a high diversity has been observed. The shells consist of columnar-prismatic, foliated, granular calcite and myostracal-prismatic aragonite. Furthermore, voids are incorporated into the ostreoid shell: the pores of the vesicular shell segments and the blades/laths of the chalk lenses. These initiate formation of additional microstructures and textures. We investigated the shells of Magallana gigas, Ostrea stentina, Ostrea edulis (Ostreidae), Hyotissa hyotis, Hyotissa mcgintyi and Neopycnodonte cochlear (Gryphaeidae) with high-resolution, low-kV, electron backscatter diffraction (EBSD) measurements and scanning electron microscopy (FE-SEM) imaging and review the diversity of ostreoid Ca-carbonate microstructures and textures. From a crystallographic perspective, we (i) characterized the sub-micrometer crystal assembly pattern of ostreoid microstructures and textures, (ii) investigated crystal organization at the changeover from one microstructure into the other and (iii) examined how curved crystal surfaces are generated at inner shell surface as well as within the shell, in and at aggregations of folia and foliated units. We show that Ostreoidea are capable of secreting single crystalline, graded and dendritic calcite within the same shell and, hence, are able to vary strongly the degree of crystal co-alignment. We demonstrate that Ostreoidea myostracal aragonite is twinned, while shell calcite is not twinned, neither within different microstructures nor at the changeover between adjacent microstructures. We highlight the very specific microstructure of the foliated shell and demonstrate the strongly regulated gradedness of both the c- and a*-axes orientation of the foliated calcite crystallites. Full article

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

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12 pages, 5723 KiB

Open AccessArticle

Regulation of the Thermoelectric Properties of Perovskite RECoO₃ Ceramics via High-Entropy Engineering

by Kezhen Zhang, Chengchao Yang, Xianpeng Ao, Yulong Zhao, Weihao Tan, Jinglong Wu, Bin Liu, Kun Dong, Liangwei Chen and Lan Yu

Crystals 2025, 15(3), 285; https://doi.org/10.3390/cryst15030285 - 20 Mar 2025

Viewed by 176

Abstract

Entropy engineering has been demonstrated to be an effective strategy to regulate the thermoelectric properties of materials. In this work, we report a series of single-phase cubic (La_0.25Sr_0.25Ba_0.25Ca_0.25)CoO₃ (LSBC), (La_0.25Nd_0.25Sr [...] Read more.

Entropy engineering has been demonstrated to be an effective strategy to regulate the thermoelectric properties of materials. In this work, we report a series of single-phase cubic (La_0.25Sr_0.25Ba_0.25Ca_0.25)CoO₃ (LSBC), (La_0.25Nd_0.25Sr_0.25Ba_0.25)CoO₃ (LNSB), and (La_0.2Nd_0.2Sr_0.2Ba_0.2Ca_0.2)CoO₃ (LNSBC) ceramics based on high-entropy design in the Re site of perovskite RECoO₃. Electron microscopy results indicate that the three samples have high crystallinity and exhibit a clear pore structure with rich lattice defects. Electrical transport measurements show that LNSB and LNSBC show metallic conductive behaviors with the lowest resistivity of only 2.25 mΩ cm at 973 K, while LSBC exhibits a semiconductor–metal transition at around 650 K due to the lower average chemical valences in the RE site. Meanwhile, the low average chemical valences also cause the increasing proportion of Co⁴⁺ due to the requirement of charge neutrality of the samples, which inhibits their Seebeck coefficients. However, compared with the reported Co-based perovskite oxides, their thermal conductivities are greatly reduced owing to high-entropy enhanced lattice scattering. LSBC in particular obtains the lowest thermal conductivity of 1.25 W·m⁻¹·K⁻¹ at 937 K, while LNSB and LNSBC characterized by high carrier thermal conductivity exhibit a thermal conductivity of 1.52 W·m⁻¹·K⁻¹ at the same temperature. These findings reveal that high-entropy design in the RE site of perovskite RECoO₃ ceramics enables the effective reduction of thermal conductivity and the maintenance of the excellent electrical properties simultaneously, which provides a novel route for the development of high-performance thermoelectric materials. Full article

(This article belongs to the Special Issue Preparation and Applications of High-Entropy Materials)

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20 pages, 4199 KiB

Open AccessArticle

The Stirring Effect on the Crystal Morphology of p-Acetamidobenzoic Acid Solution Crystallization

by Rui Dong, Fan Wang, Dingding Jing, Yong Liu and Ying Bao

Crystals 2025, 15(3), 284; https://doi.org/10.3390/cryst15030284 - 20 Mar 2025

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Abstract

This work investigates the stirring effect on p-Acetamidobenzoic Acid (p -AABA) crystal morphology through single crystal cultivation, crystal face growth rate, and nucleation supersaturation measurements, molecular simulation (MS), and computational fluid dynamics (CFD). Results show that stirring rate influences nucleation supersaturation, [...] Read more.

This work investigates the stirring effect on p-Acetamidobenzoic Acid (p -AABA) crystal morphology through single crystal cultivation, crystal face growth rate, and nucleation supersaturation measurements, molecular simulation (MS), and computational fluid dynamics (CFD). Results show that stirring rate influences nucleation supersaturation, boundary layer thickness on the {101} and {010} faces, and shear stress applied on these two faces. This leads to changes in nucleation rate, nucleus size, and relative growth rates between the {101} and {010} faces, thus affecting crystal morphology. Under low-rate stirring (150 rpm), crystals exhibit a small size, a low aspect ratio, and a clear aggregation phenomenon. Appropriately increasing stirring rate can prevent aggregation and improve particle size and crystal aspect ratio. High-rate stirring leads to a higher shear stress at the corner points of the {101} face, causing crystal fragmentation, which leads to a significant decrease in crystal size and a slow decrease in aspect ratio. Moreover, the growth rates of the {101} and {010} faces exhibit an exponential dependence on supersaturation. The {101} face grows faster than the {010} face, and this growth rate difference widens with the increasing supersaturation. This study provides a theoretical basis and practical guidance for optimizing crystal morphology in stirred solution crystallization. Full article

(This article belongs to the Section Crystal Engineering)

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15 pages, 21072 KiB

Open AccessArticle

Dynamic Colour Changes in Thermochromic Liquid Crystal Inks: Compatibility with Bacterial Nanocellulose for Sustainable Packaging Solutions

by Maja Strižić Jakovljević, Marta Klanjšek Gunde, Tomislav Cigula and Gregor Lavrič

Crystals 2025, 15(3), 283; https://doi.org/10.3390/cryst15030283 - 19 Mar 2025

Viewed by 309

Abstract

This study investigates the interaction between thermochromic liquid crystal (TLC) inks and bacterial nanocellulose (BNC), emphasizing their compatibility for smart packaging applications. While the chiral nematic structure of TLC pigments dictates their dynamic colour changing behaviour, this research focuses on how TLC inks [...] Read more.

This study investigates the interaction between thermochromic liquid crystal (TLC) inks and bacterial nanocellulose (BNC), emphasizing their compatibility for smart packaging applications. While the chiral nematic structure of TLC pigments dictates their dynamic colour changing behaviour, this research focuses on how TLC inks interact with BNC, a biodegradable and eco-friendly substrate. This study examines material compatibility, colorimetric properties, and the influence of substrate characteristics on the thermally induced colour transitions of TLC inks. Screen printing was employed to deposit TLC inks onto BNC-based films and black uncoated paper, followed by spectrometric analysis to evaluate the temperature-dependent colour response. The results indicate that BNC serves as a promising platform for TLC ink integration, enhancing its potential for intelligent packaging and indicator systems. These findings contribute to the advancement of sustainable, responsive materials for next-generation smart packaging solutions. Full article

(This article belongs to the Special Issue Advances in Thermochromic Liquid Crystals and Functional Colour-Changing Materials)

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12 pages, 2802 KiB

Open AccessArticle

Research on the Fabrication of X-Cut Near Stoichiometric Lithium Niobate Wafers

by Zixuan Dong, Qingyan Xu, Shuaijie Liang, Jiashun Si, Mengfan Wang, Xuefeng Zhang and Jilin He

Crystals 2025, 15(3), 282; https://doi.org/10.3390/cryst15030282 - 19 Mar 2025

Viewed by 271

Abstract

This article discusses the preparation of twin free X-cut lithium niobate wafers using the diffusion method. The liquid electrode method was used to eliminate parasitic microdomains at dislocations. According to research, the Li-rich lithium niobate polycrystalline material contains (Li_0.941Nb_0.059) [...] Read more.

This article discusses the preparation of twin free X-cut lithium niobate wafers using the diffusion method. The liquid electrode method was used to eliminate parasitic microdomains at dislocations. According to research, the Li-rich lithium niobate polycrystalline material contains (Li_0.941Nb_0.059) Nb_0.9528O₃ and Li₃NbO₄ phases, and the diffused near-stoichiometric lithium niobate wafer exhibits a monodomain state. The piezoelectric coefficient (d₃₃) of near-stoichiometric lithium niobate after eliminating microdomains increased by 12% compared to congruent lithium niobate. The Curie temperature of near-stoichiometric lithium niobate wafers can reach 1198 °C, and the UV absorption spectrum of near-stoichiometric lithium niobate is blue shifted by 10 nm compared to congruent lithium niobate wafers, making it more suitable for fabricating electro-optic and micro nano electronics devices. Full article

(This article belongs to the Section Industrial Crystallization)

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26 pages, 6566 KiB

Open AccessReview

The B30.2/SPRY-Domain: A Versatile Binding Scaffold in Supramolecular Assemblies of Eukaryotes

by Peer R. E. Mittl and Hans-Dietmar Beer

Crystals 2025, 15(3), 281; https://doi.org/10.3390/cryst15030281 - 19 Mar 2025

Viewed by 374

Abstract

B30.2 domains, sometimes referred to as PRY/SPRY domains, were originally identified by sequence profiling methods at the gene level. The B30.2 domain comprises a concanavalin A-like fold consisting of two twisted seven-stranded anti-parallel β-sheets. B30.2 domains are present in about 150 human and [...] Read more.

B30.2 domains, sometimes referred to as PRY/SPRY domains, were originally identified by sequence profiling methods at the gene level. The B30.2 domain comprises a concanavalin A-like fold consisting of two twisted seven-stranded anti-parallel β-sheets. B30.2 domains are present in about 150 human and 700 eukaryotic proteins, usually fused to other domains. The B30.2 domain represents a scaffold, which, through six variable loops, binds different unrelated peptides or endogenous low-molecular-weight compounds. At the cellular level, B30.2 proteins engage in supramolecular assemblies with important signaling functions. In humans, B30.2 domains are often found in E3-ligases, such as tripartite motif (Trim) proteins, SPRY domain-containing SOCS box proteins, Ran binding protein 9 and −10, Ret-finger protein-like, and Ring-finger proteins. The B30.2 protein recognizes the target and recruits the E2-conjugase by means of the fused domains, often involving specific adaptor proteins. Further well-studied B30.2 proteins are the methyltransferase adaptor protein Ash2L, some butyrophilins, and Ryanodine Receptors. Although the affinity of an isolated B30.2 domain to its ligand might be weak, it can increase strongly due to avidity effects upon recognition of oligomeric targets or in the context of macromolecular machines. Full article

(This article belongs to the Special Issue Protein Crystallography: The State of the Art)

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17 pages, 8422 KiB

Open AccessArticle

Corrosion Mechanism and Properties of 316L Stainless Steel in NaCl-KCl Molten Salt at High Temperatures

by Ruimin Lv, Xian Tang, Zhemian Ying, Hua Ai, Hua Sun, Wei Zhang, Ying Wang, Jinjuan Cheng and Long Yan

Crystals 2025, 15(3), 280; https://doi.org/10.3390/cryst15030280 - 18 Mar 2025

Viewed by 395

Abstract

The corrosion properties of 316L stainless steel (316L SS) alloy within molten NaCl-KCl salt were explored through a static immersion experiment carried out at 700 °C under Ar flow for 25, 50, 100, 200, and 400 h. The loss in weight of the [...] Read more.

The corrosion properties of 316L stainless steel (316L SS) alloy within molten NaCl-KCl salt were explored through a static immersion experiment carried out at 700 °C under Ar flow for 25, 50, 100, 200, and 400 h. The loss in weight of the corroded 316L SS alloy increased from 0.06 to 1.71 mg/cm², while the maximum corrosion depth increased from 1.71 to 14.09 μm. However, the corrosion rate initially increased from 27.54 μm/year to 93.45 μm/year and then decreased to 47.22 μm/year as the soaking time was increased from 25 to 400 h. The impurities in the molten salts produced corrosive Cl₂ and HCl, which corroded the 316L SS matrix. The accelerated selective Cr dissolution with small amounts of Fe and Ni resulted in intergranular corrosion as the time of corrosion was increased. The depletion depths for Ni, Cr, and Fe at 400 h were found to be 0.87 μm, 3.94 μm, and 1.47 μm, respectively. The formation of Cr and Fe oxides might potentially play a vital role. The grain boundary and outward diffusion of Mo may prevent the outward diffusion of Cr, thereby mitigating alloy corrosion. Therefore, molten chloride salt purification and the selection of stainless steel are crucial for developing future concentrated solar power technologies. The findings of this study provide guidelines for the use of 316L SS in NaCl-KCl salt at high temperatures. Full article

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14 pages, 9037 KiB

Open AccessArticle

Evaluation of Fracture Toughness of γ-Phase Containing Cemented Carbides by Using Through-Thickness Micronotches Shaped by Ultrashort Pulsed Laser Ablation

by Marc Serra, Ramon Batista, Núria Cinca, Elena Tarrés, Emilio Jiménez-Piqué, Pablo Moreno and Luis Llanes

Crystals 2025, 15(3), 279; https://doi.org/10.3390/cryst15030279 - 18 Mar 2025

Viewed by 240

Abstract

WC-Co cemented carbides, commonly known as hardmetals, are composite materials constituted by hard ceramic particles embedded in a ductile metal matrix. Due to their unique microstructural assemblage, these materials exhibit excellent combinations of hardness, strength, and toughness, consolidating them as a first choice [...] Read more.

WC-Co cemented carbides, commonly known as hardmetals, are composite materials constituted by hard ceramic particles embedded in a ductile metal matrix. Due to their unique microstructural assemblage, these materials exhibit excellent combinations of hardness, strength, and toughness, consolidating them as a first choice for tools, structural and wear components. During recent decades, extensive research and technological advancements have driven the development of alternative cemented carbide grades, where traditionally used WC or Co are partially or entirely replaced. Within this context, hardmetals containing a third γ-phase (mixed cubic carbides) represent an interesting alternative. However, accurate evaluation of their fracture toughness remains a significant issue, especially as conventional methods using either indentation or precracking approaches are limited by either restricted implementation of fracture mechanics analysis or testing challenges. Within this context, this study proposes, implements, and validates the use of a novel laser-micronotching methodology to evaluate the fracture toughness of a γ-phase containing cemented carbide grade. For comparison purposes, the investigation also includes assessment of such a property by means of two other well-established testing methodologies. Moreover, similar experimental work was conducted in a plain WC-Co system with similar microstructural features. It is shown that machining of a through-thickness micronotch by means of ultra-short pulsed laser ablation is a reliable and efficient method for fracture toughness evaluation of γ-phase containing hardmetals. The main reason behind this is its capability for providing a precise and reproducible micronotch, with minimal thermal damage, that finally acts as a real through-thickness crack for which a stress-intensity factor is well-defined under flexural testing. Furthermore, toughness values obtained are in satisfactory agreement with those determined using precracked specimens with machined large notches and/or indentation techniques. Full article

(This article belongs to the Special Issue Advances in New Multifunctional Hard Materials)

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16 pages, 7409 KiB

Open AccessArticle

Microstructure and Reciprocating Sliding Wear Resistance Evaluation on SiMo Ductile Iron Low Alloyed with Cobalt

by Eduardo Colin-García, Alejandro Cruz-Ramírez, Marisa Moreno-Ríos, Ricardo Gerardo Sánchez-Alvarado, José Antonio Romero-Serrano, Juan Cancio Jiménez-Lugos, Armando Irvin Martínez-Pérez and Edgar Ernesto Vera-Cárdenas

Crystals 2025, 15(3), 278; https://doi.org/10.3390/cryst15030278 - 18 Mar 2025

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Abstract

High silicon and molybdenum (SiMo) ductile irons present a metallic matrix composed principally of ferrite with little volume fraction of pearlite and carbides. In this work, two SiMo ductile irons with similar levels of silicon, 0.3% Mo (DI-0.3Mo) and 0.6% Mo with 0.8% [...] Read more.

High silicon and molybdenum (SiMo) ductile irons present a metallic matrix composed principally of ferrite with little volume fraction of pearlite and carbides. In this work, two SiMo ductile irons with similar levels of silicon, 0.3% Mo (DI-0.3Mo) and 0.6% Mo with 0.8% Co (DI-0.6Mo-0.8Co), were evaluated to determine the effect of molybdenum and cobalt on the microstructure, hardness, and wear performance at room temperature. The microstructural characterization of the ductile irons was performed using light microscopy and SEM-EDS. At the same time, mechanical characterization was carried out using Rockwell C hardness, and wear was evaluated using reciprocating ball-on-flat sliding wear tests. The result showed that DI-0.6Mo-0.8Co obtained the higher nodule count (247 nod/mm²), nodularity (86.69%), volume fraction of ferrite (78.15%), and molybdenum carbides (2.1%), while DI-0.3Mo presented a higher volume fraction of pearlite (12.8%) and free graphite (13.88%). The higher value of Rockwell C hardness with 21.29 HRC was obtained in DI-0.6Mo-0.8Co due to a higher amount of molybdenum carbides. The wear resistance shows that the DI-0.6Mo-0.8Co sample presented the highest wear resistance due to an adequate balance between a ferritic matrix reinforced by the molybdenum and cobalt addition and a high carbide content. Full article

(This article belongs to the Special Issue Microstructural Characterization and Property Analysis of Alloys)

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17 pages, 3424 KiB

Open AccessArticle

Preparation of TiO₂/α-Fe₂O₃@SiO₂ Nanorod Heterostructures and Their Applications for Efficient Photodegradation of Methylene Blue

by Yujeong Jeong, Kyubeom Lee, Gaeun Kim, Eun-Hye Jang, Youngson Choe, Seok Kim and Sungwook Chung

Crystals 2025, 15(3), 277; https://doi.org/10.3390/cryst15030277 - 17 Mar 2025

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Abstract

A facile solvo-hydrothermal method was used to synthesize sub-100 nm diameter TiO₂/α-Fe₂O₃@SiO₂ nanorods (TiO₂/HNRs@SiO₂). Thermal annealing of TiO₂/HNRs@SiO₂ activated the photosensitizing crystalline TiO₂ domains containing mixed anatase and [...] Read more.

A facile solvo-hydrothermal method was used to synthesize sub-100 nm diameter TiO₂/α-Fe₂O₃@SiO₂ nanorods (TiO₂/HNRs@SiO₂). Thermal annealing of TiO₂/HNRs@SiO₂ activated the photosensitizing crystalline TiO₂ domains containing mixed anatase and rutile phases. The photocatalytic degradation of methylene blue (MB), conducted using thermally annealed TiO₂/HNRs@SiO₂ photocatalysts, was successfully demonstrated with ~95% MB removal efficiency under mild conditions of pH = ~7 and room temperature using ~150 min of solar irradiation. The enhanced removal efficiency was attributed to the rapid adsorption of MB onto the TiO₂/HNRs@SiO₂ surface via favorable electrostatic interactions and the synergistic integration of α-Fe₂O₃ and TiO₂ into nanorod heterostructures with bandgaps of 1.99–2.03 eV, allowing them to absorb visible light for efficient photocatalytic decomposition. This study provides insights into designing photocatalysts with improved selectivity for sustainable water treatment and environmental remediation. Full article

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

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10 pages, 2739 KiB

Open AccessArticle

Influence of Milling Energy and Precursors on CaKFe₄As₄ Polycrystalline Superconductor Morphology

by Anastasiya Duchenko, Achille Angrisani Armenio, Giuseppe Celentano, Alessandra Fava, Daniele Mirabile Gattia, Nicola Pompeo, Enrico Silva, Francesca Varsano and Andrea Masi

Crystals 2025, 15(3), 276; https://doi.org/10.3390/cryst15030276 - 17 Mar 2025

Viewed by 260

Abstract

The synthesis of CaKFe₄As₄ superconducting compounds either requires the adoption of high-temperature synthesis or implies the intimate mixing of the precursors via mechanochemical routes before the thermal step in order to avoid chemical inhomogeneities that lead to thermodynamically stable unwanted [...] Read more.

The synthesis of CaKFe₄As₄ superconducting compounds either requires the adoption of high-temperature synthesis or implies the intimate mixing of the precursors via mechanochemical routes before the thermal step in order to avoid chemical inhomogeneities that lead to thermodynamically stable unwanted phases. High Energy Ball Milling (HEBM) represents a useful tool to ensure the comminution of the elements and their dispersion to obtain the target phase. The adoption of mechanochemical treatments is, however, known to lead to the formation of aggregates of small crystals, leading to a powder morphology not optimal for practical applications. In this work, we report our findings in the synthesis of CaKFe₄As₄ polycrystalline compounds showing the effect of milling energy on the morphology and phase composition of the powders. To overcome the limits of conventional synthesis, we report the results of a novel synthesis approach for CaKFe₄As₄ materials, highlighting how the choice of the proper precursors and the adoption of milder treatments can represent the key to optimizing the powder morphology. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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15 pages, 296 KiB

Open AccessArticle

Line Defects in Quasicrystals

by Markus Lazar

Crystals 2025, 15(3), 275; https://doi.org/10.3390/cryst15030275 - 17 Mar 2025

Viewed by 246

Abstract

The six-dimensional framework of the integral formalism for line defects (straight dislocations and line forces) in anisotropic elasticity has been extended to a

2 n

-dimensional integral formalism for line defects in quasicrystals (

n = 4, 5, 6

for one-, [...] Read more.

The six-dimensional framework of the integral formalism for line defects (straight dislocations and line forces) in anisotropic elasticity has been extended to a

2 n

-dimensional integral formalism for line defects in quasicrystals (

n = 4, 5, 6

for one-, two-, and three-dimensional quasicrystals) including phonon and phason fields. The elastic fields of a line defect in a quasicrystal have a surprisingly simple and compact form in the integral formalism of quasicrystals. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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17 pages, 4792 KiB

Open AccessArticle

What Is More Important When Calculating the Thermodynamic Properties of Organic Crystals, Density Functional, Supercell, or Energy Second-Order Derivative Method Choice?

by Aleksandr S. Dubok and Denis A. Rychkov

Crystals 2025, 15(3), 274; https://doi.org/10.3390/cryst15030274 - 16 Mar 2025

Viewed by 585

Abstract

Calculation of second-order derivatives of energy using the DFT method is a valuable approach for the estimation of both the thermodynamical and mechanical properties of organic crystals from the first principles. This type of calculation requires specification of several computational parameters, including the [...] Read more.

Calculation of second-order derivatives of energy using the DFT method is a valuable approach for the estimation of both the thermodynamical and mechanical properties of organic crystals from the first principles. This type of calculation requires specification of several computational parameters, including the functional, supercell, and method of phonon calculations. Nevertheless, the importance of these parameters is presented in the literature very modestly. In this work, we demonstrate the influence of these computational parameters on the accuracy of calculated second-order derivatives using the practical example of pyrazinamide polymorphs, including the plastically bending α form and the β, γ, and brittle δ form. The effects of the settings used on the resulting enthalpies of the polymorphic modifications of pyrazinamide are compared: supercell setting (primitive cell vs. appropriate supercell) has a much stronger impact than functional (PBE-D3BJ vs. Hamada rev-vdW-DF2) which in turn affects results significantly more than the method for second-order derivative computation (FD vs. DFPT approach). Finally, we propose some suggestions for choosing the right settings for calculating second-order derivatives for molecular crystals. Full article

(This article belongs to the Special Issue Computational Research on Crystals)

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18 pages, 15306 KiB

Open AccessReview

Emission Wavelength Control via Molecular Structure Design of Dinuclear Pt(II) Complexes: Optimizing Optical Properties for Red- and Near-Infrared Emissions

by Hea Jung Park

Crystals 2025, 15(3), 273; https://doi.org/10.3390/cryst15030273 - 15 Mar 2025

Viewed by 390

Abstract

Phosphorescent Pt(II) complexes have garnered significant attention as key components in luminescence-based systems due to their highly efficient emission properties. A notable characteristic of these complexes is their ability to form excimers through strong molecular stacking in concentrated solutions or solid film states. [...] Read more.

Phosphorescent Pt(II) complexes have garnered significant attention as key components in luminescence-based systems due to their highly efficient emission properties. A notable characteristic of these complexes is their ability to form excimers through strong molecular stacking in concentrated solutions or solid film states. This aggregation-driven emission, primarily arising from metal–metal to ligand charge transfer (MMLCT), is influenced by overlapping d-orbitals oriented perpendicular to the square planar structure of the Pt(II) complexes. Although this property hinders the development of pure blue-emitting Pt(II) complexes, it facilitates the design of materials that emit red- and near-infrared (NIR) light. By employing advanced molecular design techniques, dinuclear Pt(II) complexes have been optimized to significantly enhance red and NIR emissions through the modulation of Pt-Pt interactions and adjustments in ligand electron densities. This review elucidates how the control of Pt-Pt distances and strategic ligand modifications can directly influence the emission spectra toward red and NIR regions. A comparative analysis of recent studies underscores the novelty and effectiveness of double-decker-type dinuclear Pt(II) complexes in achieving efficient emission characteristics in the long-wavelength range. These insights may guide the design of molecular structures for next-generation organometallic phosphorescent materials. Full article

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

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11 pages, 2472 KiB

Open AccessArticle

Molecular Dynamics Study of the Ni Content-Dependent Mechanical Properties of NMC Cathode Materials

by Ijaz Ul Haq and Seungjun Lee

Crystals 2025, 15(3), 272; https://doi.org/10.3390/cryst15030272 - 15 Mar 2025

Viewed by 435

Abstract

Lithium nickel manganese cobalt oxides (NMCs) are widely used as cathode materials in commercial batteries. Efforts have been made to enhance battery energy density and stability by adjusting the element ratio. Nickel-rich NMC shows promise due to its high capacity; however, its commercial [...] Read more.

Lithium nickel manganese cobalt oxides (NMCs) are widely used as cathode materials in commercial batteries. Efforts have been made to enhance battery energy density and stability by adjusting the element ratio. Nickel-rich NMC shows promise due to its high capacity; however, its commercial viability is hindered by severe capacity fade, primarily caused by poor mechanical stability. To address this, understanding the chemo-mechanical behavior of Ni-rich NMC is crucial. The mechanical failure of Ni-rich NMC materials during battery operation has been widely studied through theoretical approaches to identify possible solutions. The elastic properties are key parameters for structural analysis. However, experimental data on NMC materials are scarce due to the inherent difficulty of measuring the properties of electrode active particles at such a small scale. In this study, we employ molecular dynamics (MDs) simulations to investigate the elastic properties of NMC materials with varying compositions (NMC111, NMC532, NMC622, NMC721, and NMC811). Our results reveal that elasticity increases with nickel content, ranging from 200 GPa for NMC111 to 290 GPa for NMC811. We further analyze the contributing factors to this trend by examining the individual components of the elastic properties. The simulation results provide valuable input parameters for theoretical models and continuum simulations, offering insights into strategies for reducing the mechanical instability of Ni-rich NMC materials. Full article

(This article belongs to the Special Issue Electrode Materials in Lithium-Ion Batteries)

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20 pages, 2700 KiB

Open AccessReview

A Review of Near-Infrared Reflective Nanopigments: Aesthetic and Cooling Properties

by Shehab A. Mansour and Ashraf H. Farha

Crystals 2025, 15(3), 271; https://doi.org/10.3390/cryst15030271 - 14 Mar 2025

Viewed by 446

Abstract

Excessive use of conventional cooling devices, such as air conditioners, produces an increase in the urban heat island phenomenon, which causes exacerbating climate change and environmental degradation. In response, this review focuses on the potential of near-infrared nanopigments and specifically cool nanopigments as [...] Read more.

Excessive use of conventional cooling devices, such as air conditioners, produces an increase in the urban heat island phenomenon, which causes exacerbating climate change and environmental degradation. In response, this review focuses on the potential of near-infrared nanopigments and specifically cool nanopigments as a sustainable alternative for cooling. These innovative materials have been shown to effectively reflect solar near-infrared radiation, reducing the urban heat island effect and mitigating the environmental impacts associated with conventional cooling methods. This comprehensive review explores the aesthetic and cooling aspects of near-infrared nanopigments, highlighting their properties, applications, and benefits as a promising solution for mitigating the urban heat island phenomenon and promoting a more sustainable future. Recent breakthroughs in the use of nanopigment materials are also explored. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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12 pages, 2003 KiB

Open AccessReview

Sputtered LiNbO₃ Thin Films for Application in Integrated Photonics: A Review

by Igor Kuznetsov, Anton Perin, Angelina Gulyaeva and Vladimir Krutov

Crystals 2025, 15(3), 270; https://doi.org/10.3390/cryst15030270 - 14 Mar 2025

Viewed by 419

Abstract

LiNbO₃ plays a significant role in modern integrated photonics because of its unique properties. One of the challenges in modern integrated photonics is reducing chip production cost. Today, the most widespread yet expensive method to fabricate thin films of LiNbO₃ is [...] Read more.

LiNbO₃ plays a significant role in modern integrated photonics because of its unique properties. One of the challenges in modern integrated photonics is reducing chip production cost. Today, the most widespread yet expensive method to fabricate thin films of LiNbO₃ is the smart cut method. The high production cost of smart-cut chips is caused by the use of expensive equipment for helium implantation. A prospective method to reduce the cost of photonic integrated circuits is to use sputtered thin films of lithium niobite, since sputtering technology does not require helium implantation equipment. The purpose of this review is to assess the feasibility of applying sputtered LiNbO₃ thin films in integrated photonics. This work compares sputtered LiNbO₃ thin films and those fabricated by widespread methods, including the smart cut method, liquid-phase epitaxy, chemical vapor deposition, pulsed laser deposition, and molecular-beam epitaxy. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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11 pages, 2875 KiB

Open AccessArticle

Tb³⁺-Doped LGS Crystals: Crystal Growth and Electro-Elastic Features

by Nianlong Zhang, Jipeng Wu, Hengyuan Zhang, Feifei Chen, Fapeng Yu, Li Sun and Xian Zhao

Crystals 2025, 15(3), 269; https://doi.org/10.3390/cryst15030269 - 13 Mar 2025

Viewed by 322

Abstract

Piezoelectric materials have garnered significant attention due to their diverse applications in technologies such as sensors, actuators, and energy-harvesting systems. This study focuses on the growth and characterization of Tb³⁺-doped La₃Ga₅SiO₁₄ (LGS) crystals. A novel 10% [...] Read more.

Piezoelectric materials have garnered significant attention due to their diverse applications in technologies such as sensors, actuators, and energy-harvesting systems. This study focuses on the growth and characterization of Tb³⁺-doped La₃Ga₅SiO₁₄ (LGS) crystals. A novel 10% Tb³⁺-doped single LGS crystal was successfully grown using the Czochralski method. The crystal structure and fluorescence properties were determined, and the electro-elastic properties were evaluated by the impedance method, which assessed dielectric, piezoelectric, and elastic constants. The Tb³⁺-doped crystal was observed to crystallize in the trigonal system, with the concentration of the Tb³⁺ ion in the crystal determined to be 2.50 wt%. The piezoelectric coefficients were measured as d₁₁ = 5.41 pC/N and d₁₄ = −5.52 pC/N, and the dielectric constants were found to be 19.60 and 52.75, respectively. The temperature-dependent behavior of Tb:LGS crystals was investigated, particularly concerning their elastic constants, demonstrating favorable thermal stability. This study provides valuable insights into the relationship between the crystals’ structural characteristics and performance. Additionally, the fluorescence properties were measured; a long lifetime (τ = 1.655 ms) indicated the potential applications of Tb:LGS crystals in laser technology. Full article

(This article belongs to the Special Issue New Insights into Optical Crystals: From Fundamentals to Materials Performance)

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21 pages, 22532 KiB

Open AccessArticle

Influence of Rotational Speed on the Microstructure and Mechanical Properties of Refill Friction Stir Spot Welded Pure Copper

by Xiaole Ge, I. N. Kolupaev, Di Jiang, Weiwei Song and Hongfeng Wang

Crystals 2025, 15(3), 268; https://doi.org/10.3390/cryst15030268 - 13 Mar 2025

Viewed by 327

Abstract

Refill friction stir spot welding (RFSSW) is an effective technique for achieving high-quality joints in metallic materials, with rotational speed being a critical parameter influencing joint quality. Current research on RFSSW has primarily focused on low-melting-point materials such as aluminum alloys, while limited [...] Read more.

Refill friction stir spot welding (RFSSW) is an effective technique for achieving high-quality joints in metallic materials, with rotational speed being a critical parameter influencing joint quality. Current research on RFSSW has primarily focused on low-melting-point materials such as aluminum alloys, while limited attention has been given to pure copper, a material characterized by its high-melting-point and high-thermal-conductivity. This study aims to investigate the effects of rotational speed on the microstructure and mechanical properties of RFSSW joints in pure copper. To achieve this goal, welding experiments were conducted at five rotational speeds. The welding defects, microstructure, and hook morphology of the welded joints were analyzed, while the variations in axial force and torque during welding were studied. The influence of rotational speed on the microhardness and tensile-shear failure load of the welded joints was explored, and the fracture modes of the welded joints at different rotational speeds were discussed. The results indicated that the primary welding defects were incomplete refill and surface unevenness. Higher rotational speeds resulted in coarser microstructures in the stir zones. As the rotational speed increased, the hook height progressively rose, the peak axial force showed an increasing trend, and the peak torque continuously decreased. The high microhardness points in the welded joints were predominantly located at the top of the sleeve stir zone (S-Zone), while the low microhardness points were observed at the center of the pin stir zone (P-Zone) and in the heat-affected zone (HAZ). The tensile-shear failure load of the welded joints initially increased and then decreased on the whole with the rising rotational speed, peaking at 5229 N at a rotational speed of 1200 rpm. At lower rotational speeds, the fracture type of the welded joints was characterized as plug fracture. Within the rotational speed range of 1200 rpm to 1600 rpm, the fracture type transitioned to upper sheet fracture. The initial fractures under different rotational speeds exhibited ductile fracture. This study contributes to advancing the understanding of RFSSW characteristics in high-melting-point and high-thermal-conductivity materials. Full article

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

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15 pages, 8753 KiB

Open AccessArticle

Dielectric Passivation Treatment of InGaN MESA on Si Substrates for Red Micro-LED Application

by Hongyu Qin, Shuhan Zhang, Qian Fan, Xianfeng Ni, Li Tao and Xing Gu

Crystals 2025, 15(3), 267; https://doi.org/10.3390/cryst15030267 - 13 Mar 2025

Viewed by 497

Abstract

The emergence of GaN-based micro-LEDs has revolutionized display technologies due to their superior brightness, energy efficiency, and thermal stability compared to traditional counterparts. However, the development of red-emitting micro-LEDs on silicon substrates (GaN-on-Si) faces significant challenges, among them including hydrogen-induced deactivation of p-GaN [...] Read more.

The emergence of GaN-based micro-LEDs has revolutionized display technologies due to their superior brightness, energy efficiency, and thermal stability compared to traditional counterparts. However, the development of red-emitting micro-LEDs on silicon substrates (GaN-on-Si) faces significant challenges, among them including hydrogen-induced deactivation of p-GaN caused by hydrogen species generated from SiH₄ decomposition during SiO₂ passivation layer growth, which degrades device performance. This study systematically investigates the use of high-density metal-oxide dielectric passivation layers deposited by atomic layer deposition (ALD), specifically Al₂O₃ and HfO₂, to mitigate these effects and enhance device reliability. The passivation layers effectively suppress hydrogen diffusion and preserve p-GaN activation, ensuring improved ohmic contact formation and reduced forward voltage, which is measured by the probe station. The properties of the epitaxial layer and the cross-section morphology of the dielectric layer were characterized by photoluminescence (PL) and scanning electron microscopy (SEM), respectively. Experimental results reveal that Al₂O₃ exhibits superior thermal stability and lower current leakage under high-temperature annealing, while HfO₂ achieves higher light-output power (LOP) and efficiency under increased current densities. Electroluminescence (EL) measurements confirm that the passivation strategy maintains the intrinsic optical properties of the epitaxial wafer with minimal impact on Wp and FWHM across varying process conditions. The findings demonstrate the efficacy of metal-oxide dielectric passivation in addressing critical challenges in InGaN red micro-LED on silicon substrate fabrication, contributing to accelerating scalable and efficient next-generation display technologies. Full article

(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)

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13 pages, 5346 KiB

Open AccessArticle

Effect of Filler-Wire Composition on Microstructure and Properties of Al/Steel-Welded Joints by Laser Welding–Brazing

by Wenxuan Guo, Mingfang Wu, Lu Teng, Lutao Liu and Hao Wan

Crystals 2025, 15(3), 266; https://doi.org/10.3390/cryst15030266 - 13 Mar 2025

Cited by 1 | Viewed by 319

Abstract

Laser welding–brazing experiments with 6061 aluminum alloy and Q235 steel were conducted using AlSi12 and ZnAl22 as filler metals. The macroscopic morphologies and microstructures of welding–brazing joints were analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). The effects of Si and [...] Read more.

Laser welding–brazing experiments with 6061 aluminum alloy and Q235 steel were conducted using AlSi12 and ZnAl22 as filler metals. The macroscopic morphologies and microstructures of welding–brazing joints were analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). The effects of Si and Zn elements in filler wires on the macroscopic morphologies, interfacial microstructures, tensile properties, and corrosion resistances of joints were studied. The results show that the wettability of ZnAl22-filler wire was better than that of AlSi12-filler wire. The fusion zone of the joint welded with AlSi12-filler wire consisted of α–Al solid solution and Al–Si eutectic mixture, while the interfacial reaction zone was composed of η-Fe₂(Al, Si)₅ and τ₅-Fe_1.8Al_7.2Si. The fusion zone of the joint formed using AlZn22-filler wire consisted of α–Al solid solution, η-Zn solid solution, and ZnAl eutectic structure. The joint welded with AlSi12-filler wire showed better tensile strength and corrosion resistance compared to that welded with ZnAl22-filler wire. Full article

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

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17 pages, 4834 KiB

Open AccessReview

Advancements in the Research on the Preparation and Growth Mechanisms of Various Polymorphs of Calcium Carbonate: A Comprehensive Review

by Cheng-Gong Lu, Chu-Jie Jiao, Xiu-Cheng Zhang, Jian-Sheng Zheng and Xue-Fei Chen

Crystals 2025, 15(3), 265; https://doi.org/10.3390/cryst15030265 - 13 Mar 2025

Viewed by 465

Abstract

Calcium Carbonate (CC) exhibits broad application prospects and significant market demand due to its diverse polymorphs, each with distinct potential for application in various fields. Consequently, the preparation of CC with specific polymorphs has emerged as a research hotspot. This paper commences with [...] Read more.

Calcium Carbonate (CC) exhibits broad application prospects and significant market demand due to its diverse polymorphs, each with distinct potential for application in various fields. Consequently, the preparation of CC with specific polymorphs has emerged as a research hotspot. This paper commences with an overview of the structure of CC, followed by an analysis of the advantages and disadvantages, as well as the mechanisms, of common preparation methods such as physical methods, chemical carbonation processes, and double displacement reactions. Special emphasis is placed on elucidating the influence of polymorph control agents (including inorganic ions, sugars, alcohols, and acids), process conditions (temperature, stirring rate, pH, and solution mixing rate), and reactor configurations (rotating packed beds and high-gravity reactors) on the polymorph regulation of CC. This paper points out how these factors alter the crystal formation process. Furthermore, it introduces the nucleation and growth control of CC crystallization, analyzing the mechanisms underlying these two processes. Research indicates that the carbonation process is currently a relatively mature preparation technique, with multiple factors synergistically influencing the polymorph and particle size of CC. Future efforts should focus on further improving production processes, exploring novel polymorph control agents, and delving deeper into the intrinsic mechanisms of polymorph control to achieve efficient preparation of diverse CC types. Full article

(This article belongs to the Special Issue Crystalline Materials: Polymorphism)

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37 pages, 10920 KiB

Open AccessArticle

Integration of Hybrid Machine Learning and Multi-Objective Optimization for Enhanced Turning Parameters of EN-GJL-250 Cast Iron

by Yacine Karmi, Haithem Boumediri, Omar Reffas, Yazid Chetbani, Sabbah Ataya, Rashid Khan, Mohamed Athmane Yallese and Aissa Laouissi

Crystals 2025, 15(3), 264; https://doi.org/10.3390/cryst15030264 - 12 Mar 2025

Viewed by 496

Abstract

This study aims to optimize the turning parameters for EN-GJL-250 grey cast iron using hybrid machine learning techniques integrated with multi-objective optimization algorithms. The experimental design focused on evaluating the impact of cutting tool type, testing three tools: uncoated and coated silicon nitride [...] Read more.

This study aims to optimize the turning parameters for EN-GJL-250 grey cast iron using hybrid machine learning techniques integrated with multi-objective optimization algorithms. The experimental design focused on evaluating the impact of cutting tool type, testing three tools: uncoated and coated silicon nitride (Si₃N₄) ceramic inserts and coated cubic boron nitride (CBN). Key cutting parameters such as depth of cut (ap), feed rate (f), and cutting speed (Vc) were varied to examine their effects on surface roughness (Ra), cutting force (Fr), and power consumption (Pc). The results showed that the coated Si₃N₄ tool achieved the best surface finish, with minimal cutting force and power consumption, while the uncoated Si₃N₄ and CBN tools performed slightly worse. Advanced optimization models including improved grey wolf optimizer–deep neural networks (DNN-IGWOs), genetic algorithm–deep neural networks (DNN-GAs), and deep neural network–extended Kalman filters (DNN-EKF) were compared with traditional methods like Support Vector Machines (SVMs), Decision Trees (DTs), and Levenberg–Marquardt (LM). The DNN-EKF model demonstrated exceptional predictive accuracy with an R² value of 0.99. The desirability function (DF) method identified the optimal machining parameters for the coated Si₃N₄ tool: ap = 0.25 mm, f = 0.08 mm/rev, and Vc = 437.76 m/min. At these settings, Fr ranged between 46.424 and 47.405 N, Ra remained around 0.520 µm, and Pc varied between 386.518 W and 392.412 W. The multi-objective grey wolf optimization (MOGWO) further refined these parameters to minimize Fr, Ra, and Pc. This study demonstrates the potential of integrating machine learning and optimization techniques to significantly enhance manufacturing efficiency. Full article

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13 pages, 2649 KiB

Open AccessArticle

First-Principles and PSO-Driven Exploration of Ca-Pt Intermetallics: Stable Phases and Pressure-Driven Transitions

by Yifei Wang and Dengjie Yan

Crystals 2025, 15(3), 263; https://doi.org/10.3390/cryst15030263 - 12 Mar 2025

Viewed by 325

Abstract

In this study, first-principles calculations in conjunction with the particle swarm optimization (PSO) algorithm structure search method were employed to investigate the stable phases of Ca-Pt intermetallic compounds under various pressure conditions. The previously reported CaPt₅ phase and the hitherto unreported phases [...] Read more.

In this study, first-principles calculations in conjunction with the particle swarm optimization (PSO) algorithm structure search method were employed to investigate the stable phases of Ca-Pt intermetallic compounds under various pressure conditions. The previously reported CaPt₅ phase and the hitherto unreported phases Ca₃Pt and Ca₂Pt were successfully predicted, perfecting the known phase diagram for Ca-Pt intermetallic compounds. Furthermore, the pressure-induced phase transition in Ca₂Pt has been identified. The structure of Ca₂Pt undergoes a phase transition from Cmmm to C2/m and then to Cm at pressures ranging from 25 to 75 GPa. Electronic properties analyses revealed stable metallic bonds between the Ca and Pt atoms in the Ca-Pt intermetallic compounds. Simultaneously, the anionic character of the Pt atoms and the localization of electrons within the intermetallic compounds were observed. Analysis of the mechanical properties showed that Ca₃Pt and CaPt₅ exhibited different degrees of anisotropy. The CaPt₅ structure exhibits significant transverse isotropy, whereas the Ca₃Pt structure exhibits pronounced anisotropic behavior. The results of this study provide theoretical support for further research on Ca-Pt intermetallic compounds and the expansion of Pt oxidation states. Full article

(This article belongs to the Special Issue Properties of Transition Metals and Their Compounds at Extreme Conditions (2nd Edition))

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14 pages, 4981 KiB

Open AccessArticle

Modification of Lithium-Rich Layered Material Li_1.5Ni_0.17Co_0.16Mn_0.67O_2.5 Coated with Solid Electrolyte (Li₂ZrO₃)

by Bo Liao, Han Wu, Siqin Bator, Wei Li, Xiaotao Wang, Jinyu Tan, Shixiang Sun, Jingwen Cui, Yingqun Li and Xiao Tian

Crystals 2025, 15(3), 262; https://doi.org/10.3390/cryst15030262 - 11 Mar 2025

Viewed by 370

Abstract

With the rising popularity of electric vehicles and the widespread deployment of energy storage power stations. The demand for high-energy-density lithium-ion batteries is increasing day by day. Lithium-rich layered materials are among the most promising candidates for the cathode of next-generation lithium-ion batteries [...] Read more.

With the rising popularity of electric vehicles and the widespread deployment of energy storage power stations. The demand for high-energy-density lithium-ion batteries is increasing day by day. Lithium-rich layered materials are among the most promising candidates for the cathode of next-generation lithium-ion batteries due to their high energy density, cost-effectiveness, and advantages in safety and environmental protection. However, the occurrence of side reactions between lithium-rich layered materials and electrolytes has led to poor performance in later stages, posing challenges to their commercial viability. In this study, we enhance the electrochemical performance of lithium-rich layered cathode materials by applying varying amounts of solid electrolyte Li₂ZrO₃ as a coating on their surfaces. By precipitating ZrO₂ onto the surface of the precursor, we successfully sinter both the lithium-rich layered material and the coated material simultaneously, thereby reducing processing costs. The experimental results show that the coated material has more excellent electrochemical performance, specifically, when the coating amount is 1%, compared with the uncoated sample, the first Coulombic efficiency is improved from 56.9% to 63%, and after 500 charge/discharge cycles, the coated sample still has a capacity retention rate of more than 60%; Additionally, the Li₂ZrO₃ coating significantly improves the rate performance of the material, at a rate of 5 C, the specific discharge capacity improved from 102.2 mAh·g⁻¹ for the uncoated material to 137.3 mAh·g⁻¹. The reaction mechanism was investigated by cyclic voltammetry and AC impedance test, and the results showed that the appropriate amount of Li₂ZrO₃ coating can effectively reduce the side reaction between the material and the electrolyte, improve the transport performance of lithium ions in the material, and then enhance the overall electrochemical performance of the material. Full article

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

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13 pages, 6224 KiB

Open AccessArticle

The Impact of GaN Crystal Growth on Ammonia Flow Dynamics in Ammonothermal Processes

by Marek Zak, Pawel Kempisty, Boleslaw Lucznik, Robert Kucharski and Michal Bockowski

Crystals 2025, 15(3), 261; https://doi.org/10.3390/cryst15030261 - 11 Mar 2025

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Abstract

A computational fluid dynamics simulation was developed for the growth zone of gallium nitride crystallized using the alkaline ammonothermal method, considering the geometry of the seed crystals and the installation setup. The model focuses on temperature and velocity distributions, revealing turbulent and transient [...] Read more.

A computational fluid dynamics simulation was developed for the growth zone of gallium nitride crystallized using the alkaline ammonothermal method, considering the geometry of the seed crystals and the installation setup. The model focuses on temperature and velocity distributions, revealing turbulent and transient flow characteristics. Significant findings include the effect of crystal thickness on temperature and velocity changes, as well as the relationship between temperature distribution and growth rate. The results indicate that transient variations in flow and thermal fields affect the uniformity of growth and structural quality of the crystals. The paper contributes to optimizing ammonothermal crystallization processes by addressing critical parameters such as turbulence, thermal mixing, and crystal geometry. Full article

(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)

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13 pages, 7809 KiB

Open AccessArticle

Effects of Nanostructured Functional Ceramics Additives Coatings Electrode on the Structure and Mechanical Properties of SMAW Welded Joints

by Saidov R. Mannapovitch, Rakhimov R. Khamidovich, Kamel Touileb and Joffin Ponnore

Crystals 2025, 15(3), 260; https://doi.org/10.3390/cryst15030260 - 11 Mar 2025

Viewed by 381

Abstract

The present work is a comparative analysis of the properties of welded joints obtained during welding with the developed welding electrodes containing additives of photocatalysts of nanostructured functional ceramics (PNFC) brand ZB-1 (IMAN-7) and the ESAB E6013 welding electrodes. This study investigates the [...] Read more.

The present work is a comparative analysis of the properties of welded joints obtained during welding with the developed welding electrodes containing additives of photocatalysts of nanostructured functional ceramics (PNFC) brand ZB-1 (IMAN-7) and the ESAB E6013 welding electrodes. This study investigates the weld morphology, microstructure, and mechanical properties of Shield metal arc welding (SMAW) welded joints. The results of the studies showed that the introduction of PNFC brand ZB-1 into the coating of welding electrodes up to 1% has a beneficial effect on the melting ability and stability of the welding arc, formation of the bead, microstructure of the weld bead, and mechanical properties of the welded joints. It was found that IMAN-7 electrodes, compared to the ESAB E6013 electrodes, have better performance in terms of arc penetration, bead metal structure, and relative elongation of welded joints. In addition, the high melting capacity of the IMAN-7 electrode allows for economic advantages, such as increased productivity and a two-fold reduction in electrode consumption. Full article

(This article belongs to the Special Issue Welding and Joining of Metallic Materials: Microstructure and Mechanical Properties, 2nd Edition)

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9 pages, 1589 KiB

Open AccessArticle

Design of GaN-Based Laser Diode Structures with Nonuniform Doping Distribution in a p-AlGaN Cladding Layer for High-Efficiency Operation

by Chibuzo Onwukaeme and Han-Youl Ryu

Crystals 2025, 15(3), 259; https://doi.org/10.3390/cryst15030259 - 11 Mar 2025

Viewed by 449

Abstract

In GaN-based laser diode (LD) structures, it is essential to optimize the doping concentration and profiles in p-type-doped layers because of the trade-off between laser power and operation voltage as the doping concentration varies. In this study, we proposed GaN-based blue LD structures [...] Read more.

In GaN-based laser diode (LD) structures, it is essential to optimize the doping concentration and profiles in p-type-doped layers because of the trade-off between laser power and operation voltage as the doping concentration varies. In this study, we proposed GaN-based blue LD structures with nonuniform doping distributions in the p-AlGaN cladding layer to reduce the modal loss and demonstrated improved efficiency characteristics using numerical simulations. We compared the laser power, operation voltage, and wall-plug efficiency (WPE) of LDs with uniform, linear, and quadratic doping profiles in the p-AlGaN cladding layer. As the doping concentration becomes increasingly inhomogeneous, the laser output power increases significantly because of the reduced overlap of the laser mode with the p-AlGaN cladding layer. However, this nonuniform doping profile also leads to an increase in the operation voltage due to the expansion of the low-doping region. By optimizing the nonuniform doping distribution in the p-type cladding layer, the WPE was found to be improved by over 5% compared to a conventional uniformly doped p-cladding layer. The proposed design of LD structures is expected to enhance the efficiency of high-power GaN-based LDs. Full article

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

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11 pages, 4438 KiB

Open AccessArticle

Effects of Zr Alloying on Microstructure Evolution and Mechanical Properties of CoCrNi Medium Entropy Alloy

by Ao Li, Zurong Gong, Dong Li, Xiaohong Wang, Yunting Su, Tengfei Ma, Bin Liu and Baochen Zhang

Crystals 2025, 15(3), 258; https://doi.org/10.3390/cryst15030258 - 10 Mar 2025

Viewed by 396

Abstract

Alloying provides an effective approach to designing metallic materials with unique microstructures and enhanced performance. In this work, we developed a series of (CoCrNi)_100−xZr_x (where x = 1, 2, 3, 4, and 5) medium entropy alloys (MEAs) by vacuum arc-melting [...] Read more.

Alloying provides an effective approach to designing metallic materials with unique microstructures and enhanced performance. In this work, we developed a series of (CoCrNi)_100−xZr_x (where x = 1, 2, 3, 4, and 5) medium entropy alloys (MEAs) by vacuum arc-melting method. The effects of Zr addition on the microstructures and mechanical properties of (CoCrNi)_100−xZr_x MEAs were systematically investigated. Due to the negative mixing enthalpy of Zr with Co, Cr, and Ni, lamellar C15 Laves-phase precipitates formed within the ductile FCC matrix. As the Zr content increases, the alloys exhibit higher strength but become more brittle at room temperature. Among the (CoCrNi)_100−xZr_x MEAs series, the CoCrNiZr₃ MEA shows an excellent balance between strength and ductility, achieving a compressive yield strength of 610 MPa and a hardness of 249 HV, respectively, while maintaining a good ductility beyond 45%. Microstructural analysis using scanning electron microscope and transmission electron microscope suggests that this outstanding strength-ductility balance of CoCrNiZr₃ MEA arises from the synergistic effect of precipitation strengthening and solid solution strengthening. These findings not only provide deeper insight into the interaction between different strengthening mechanisms but also offer valuable guidance for designing high-performance multi-component alloys through strategic alloying. Full article

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

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