Crystals

2 pages, 125 KB

Open AccessCorrection

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

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

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

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

13 pages, 2613 KB

Open AccessArticle

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

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

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

Abstract

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

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

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

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9 pages, 6205 KB

Open AccessArticle

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

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

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

Abstract

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

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

(This article belongs to the Section Inorganic Crystalline Materials)

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29 pages, 6023 KB

Open AccessReview

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

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

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

Abstract

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

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

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

11 pages, 10416 KB

Open AccessArticle

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

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

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

Abstract

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

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

\bar{3}

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

(This article belongs to the Section Polycrystalline Ceramics)

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20 pages, 12098 KB

Open AccessArticle

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

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

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

Abstract

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

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

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

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25 pages, 69895 KB

Open AccessReview

Sodium-Based Germanate Garnet Phosphors: Fundamentals, Luminescence Regulation and Applications

by Jiajun Feng, Qiuhua Huang, Caiyuan Wen, Kunlin Wang, Shiting Chen, Keyi Fang, Peixuan Chen, Lianfen Chen and Xiang Li

Crystals 2026, 16(8), 518; https://doi.org/10.3390/cryst16080518 - 6 Aug 2026

Abstract

Garnet-structured compounds have long been recognized as versatile host platforms for luminescent phosphors, owing to their robust chemical stability and highly tunable cationic sublattices. Conventional aluminate and gallate garnets, however, generally face intrinsic limitations, including severe concentration quenching at high dopant levels, relatively [...] Read more.

Garnet-structured compounds have long been recognized as versatile host platforms for luminescent phosphors, owing to their robust chemical stability and highly tunable cationic sublattices. Conventional aluminate and gallate garnets, however, generally face intrinsic limitations, including severe concentration quenching at high dopant levels, relatively high phonon energy, and unsatisfactory efficiency for long-wavelength near-infrared (NIR) emission. In recent years, sodium-based germanate garnets, constructed by introducing aliovalent Na⁺ into dodecahedral sites combined with Ge⁴⁺ substitution in tetrahedral frameworks, have emerged as a promising branch of garnet phosphors. The aliovalent Na+ incorporation brings unique structural effects, including energy migration blocking, coordination environment distortion, and defect level modulation, which endow the materials with advantages in mitigating concentration quenching, boosting energy transfer efficiency, and enhancing thermal stability. This review systematically summarizes the crystal structure classification and luminescence fundamentals of sodium-based germanate garnet systems, and introduces mainstream synthesis techniques represented by the high-temperature solid-state method. Focusing on representative host systems, the luminescence characteristics and energy transfer mechanisms of both rare earth- and transition metal-doped systems are elaborated in detail, followed by a summary of four representative performance regulation strategies: cationic disorder engineering, crystal field engineering, defect engineering and dual-site cooperative regulation. The multifunctional applications of these materials in white light-emitting diodes, plant growth lighting, fluorescence temperature sensing, NIR imaging, and information encryption are also presented. Finally, existing challenges and future research perspectives are proposed to provide guidance for the development of high-performance garnet phosphors. Full article

(This article belongs to the Special Issue Scintillator Crystals: Structure, Characterization and Scintillation Models)

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13 pages, 9139 KB

Open AccessArticle

High-Temperature Polymorphic Phase Transitions in MH₂PO₄ (M = K, Rb, Cs) Proton Conductors

by Cristian E. Botez, Zachary Musslewhite, Alex D. Price and Chunqiang Li

Crystals 2026, 16(8), 517; https://doi.org/10.3390/cryst16080517 - 6 Aug 2026

Abstract

We used powder X-ray diffraction (XRD) and ac impedance spectroscopy to investigate the polymorphic phase transitions undergone by the MH₂PO₄ (M = Cs, K, Rb) proton conductor series upon heating. High-pressure methods used in conjunction with energy dispersive XRD enhanced [...] Read more.

We used powder X-ray diffraction (XRD) and ac impedance spectroscopy to investigate the polymorphic phase transitions undergone by the MH₂PO₄ (M = Cs, K, Rb) proton conductor series upon heating. High-pressure methods used in conjunction with energy dispersive XRD enhanced by synchrotron radiation allowed us to isolate a pure cubic (superprotonic) RbH₂PO₄ (RDP) polymorph (at P = 1.2 GPa and T = 320 °C) and collect data of enough quality to Rietveld refine its crystal structure. Our data and analysis reveal that cubic RDP (Pm-3m, a = 4.76 ± 0.01 Å) is described by a unit cell where Rb and P atoms are in (0, 0, 0) and (0.5, 0.5, 0.5) positions, respectively, whereas O atoms are in (0.5, 0.234(5) 0.342(6)) positions having a multiplicity of 24 and an occupancy of 0.166. This results in dynamically disordered PO₄ tetrahedra that enables the superprotonic conduction in RDP, a mechanism like the one in the high-temperature cubic phase of the Cs-based compound CsH₂PO₄ (CDP). This is a notable behavior, as RDP and CDP are structurally different at room temperature—RDP is tetragonal (I-42d) and CDP is monoclinic (P2₁/m)—but following polymorphic modifications upon heating they both end up in superprotonic cubic phases that are isostructural to one another. On the other hand, we found that although the K-based phosphate KH₂PO₄ (KDP) has the same crystal structures as RDP at room and at intermediate temperatures, further heating does not lead to a cubic KDP phase. Overall, our results are significant from both the fundamental and applied perspective as superprotonic phosphates are promising materials for fuel cell electrolyte applications. Full article

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

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17 pages, 19481 KB

Open AccessArticle

Mineralogical and Compositional Characteristics of Argentine Red–White Banded Rhodochrosite with Ca-Poor White Bands

by Luyan Jiang, Qingfeng Guo, Can Cui and Nannan Wang

Crystals 2026, 16(8), 516; https://doi.org/10.3390/cryst16080516 - 5 Aug 2026

Abstract

Three commercial red–white banded rhodochrosite samples sold as Argentine “Rosa del Inca” material were investigated using conventional gemological observation, mineralogical analysis, micro-area chemical analysis, and spectroscopy. The red and white bands differ in color, transparency, and microstructure. However, both bands are mainly rhodochrosite. [...] Read more.

Three commercial red–white banded rhodochrosite samples sold as Argentine “Rosa del Inca” material were investigated using conventional gemological observation, mineralogical analysis, micro-area chemical analysis, and spectroscopy. The red and white bands differ in color, transparency, and microstructure. However, both bands are mainly rhodochrosite. No evidence indicates that calcite, dolomite, or other Ca-bearing carbonate minerals are the main phases in the white bands. Representative EPMA analyses of LMK-02 show that the analyzed white-band points tend to contain slightly lower Mn and relatively higher Fe and Mg than the red-band points, while CaO is below the detection limit at all representative EPMA positions. Micro-XRF mapping of LMK-02 reveals only local and discontinuous enrichments of Ca and Zn; however, the mineralogical identity and occurrence mode of these enriched domains remain unresolved. Combined with the EPMA data, the XRD, FTIR, Raman, and UV–Vis results do not support marked Ca enrichment, extensive Ca substitution for Mn, or abundant Ca-bearing carbonate phases in the analyzed white bands of LMK-02. Instead, the results indicate Ca-poor compositional variation within rhodochrosite, with the representative EPMA data showing a descriptive tendency toward slightly lower MnO and relatively higher FeO and MgO contents in the analyzed white-band points. Full article

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

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19 pages, 12556 KB

Open AccessArticle

Precursor-Directed Synthesis of CuO Nanostructures: Correlating Morphology, Surface Shell Chemistry, Porosity, and Colloidal Behavior

by Ioan Ovidiu Pană, Simona Guțoiu, Sanda Boca, Maria Suciu, Răzvan Hirian, Maria Olimpia Miclăuș, Septimiu Cassian Tripon, Cristian Leoștean and Lucian Barbu

Crystals 2026, 16(8), 515; https://doi.org/10.3390/cryst16080515 - 4 Aug 2026

Abstract

Nanostructured copper oxide (CuO) holds significant promise for optoelectronic, photocatalytic, and biomedical applications, yet its performance is critically dictated by its morphology, crystallite size, and surface chemistry. In this work, pure monoclinic CuO nanoparticles were successfully synthesized via a facile, kinetically controlled aqueous [...] Read more.

Nanostructured copper oxide (CuO) holds significant promise for optoelectronic, photocatalytic, and biomedical applications, yet its performance is critically dictated by its morphology, crystallite size, and surface chemistry. In this work, pure monoclinic CuO nanoparticles were successfully synthesized via a facile, kinetically controlled aqueous co-precipitation route using three distinct precursor salts: copper acetate (CO-Ac), copper sulfate (CO-S), and copper chloride (CO-Cl). To achieve precise architectural control, the synthesis was conducted near the thermodynamic solubility limit of the precursors combined with an abrupt NaOH injection, effectively decoupling the nucleation stage from crystal growth. Rietveld refinement of X-ray diffraction (XRD) data confirmed the structural integrity of the monoclinic lattice across all samples, χ² = 1.04 − 2.02, crystallinity 53–55%, while demonstrating that the precursor anion strongly governs the volume-averaged crystallite size, which expanded from 16 nm (CO-Ac) to 30 nm (CO-S) and 52 nm (CO-Cl). Morphological analyses revealed that acetate acts as a non-specific capping ligand, promoting isotropic, quasi-spherical nanoparticles that aggregate into high-surface-area (69.04 m²/g) “bead-chain” assemblies. Conversely, sulfate and chloride ions act as shape-directing agents via facet-selective adsorption on nucleation seeds, yielding two-dimensional plates and anisotropic acicular/needle-like architectures, respectively. X-ray photoelectron spectroscopy (XPS) and modified Auger parameter (α ~1851 eV) analyses confirmed the absolute dominance of Cu²⁺ states, with a minor fraction (~2.5 mol %) of lower-coordinated surface edge states. XPS further unveiled that the strongly alkaline environment (pH ~14) drives precursor-dependent surface chemistry: CO-Ac nanoparticles retain a clean, hydroxylated layer with minor acetate residues, whereas CO-S and CO-Cl samples develop a passive copper hydroxycarbonate (Cu₂(OH)₂CO₃) surface barrier that blocks active sites and reduces porosity. Optical properties analyzed via UV-vis diffuse reflectance revealed a pronounced, size-dependent blueshift relative to bulk CuO, with fundamental indirectly allowed bandgaps of 2.6 eV, 2.36 eV and 1.93 eV for CO-Ac, CO-S and CO-Cl samples, while the direct bandgaps shifted from 3.0 eV, 3.2 eV, and 3.57 eV for the mentioned samples. This behavior is attributed to quantum confinement governed by fine individual nanocrystals. These findings establish that precursor engineering offers a robust pathway to tailor the morphological, optical, and interfacial properties of CuO nanostructures for targeted functional devices. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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12 pages, 6650 KB

Open AccessArticle

Atmospheric-Pressure Plasma Jet Treatment Triggers Early Sintering-Related Microstructural Changes in 3Y-TZP Green Body

by Chuyue Yang, Jizhe Lyu, Xunning Cao and Xiaoqiang Liu

Crystals 2026, 16(8), 514; https://doi.org/10.3390/cryst16080514 - 4 Aug 2026

Abstract

To evaluate whether atmospheric-pressure plasma jet (APPJ) treatment induced early, sintering-related, surface microstructural variations in 3 mol% yttria-stabilized zirconia (3Y-TZP), with a particular focus on how treatment time affected the grain size and SEM-derived surface dark-area fraction, this exploratory study examined time-dependent surface [...] Read more.

To evaluate whether atmospheric-pressure plasma jet (APPJ) treatment induced early, sintering-related, surface microstructural variations in 3 mol% yttria-stabilized zirconia (3Y-TZP), with a particular focus on how treatment time affected the grain size and SEM-derived surface dark-area fraction, this exploratory study examined time-dependent surface microstructural changes in commercial 3 mol% yttria-stabilized zirconia (3Y-TZP) subjected to air APPJ exposure for 4, 8, 15, 30, or 60 min under fixed device settings. A separate no-dwell furnace reference series was used to contextualize surface microstructural changes during heating; it was not used to assign an equivalent temperature to APPJ exposure. Field-emission scanning electron microscopy was used to determine surface grain dimensions and a threshold-derived surface dark-area fraction. No specimen-surface temperature was recorded during APPJ exposure. Surface grain dimensions remained similar through 15 min and increased at 30 and 60 min, whereas the surface dark-area fraction changed modestly. Under the tested conditions, prolonged APPJ exposure was associated with marked surface grain coarsening and limited change in the SEM-derived dark-area fraction. Full article

(This article belongs to the Special Issue Nanocrystalline Materials Processing and Characterization)

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37 pages, 13423 KB

Open AccessArticle

Crystallographic Characteristics of Crossed Mollusc Shell Microstructures with Particular Focus on Scaphopod Shell Crystal Organization

by Erika Griesshaber, Sebastian Hoerl, Miguel A. Godoy-Bermúdez, Daniel Weller, Carmen Salas, Alejandro Rodríguez-Navarro, Antonio G. Checa and Wolfgang W. Schmahl

Crystals 2026, 16(8), 513; https://doi.org/10.3390/cryst16080513 - 3 Aug 2026

Abstract

Scaphopod molluscs are marine, infaunal, cosmopolitan animals. They encase their soft tissue with an aragonitic tusk-shaped shell that has at its two ends an orifice, the aperture and the apex. We investigated the shell of the dentaliid species Fissidentalium metivieri and Antalis weinkauffi [...] Read more.

Scaphopod molluscs are marine, infaunal, cosmopolitan animals. They encase their soft tissue with an aragonitic tusk-shaped shell that has at its two ends an orifice, the aperture and the apex. We investigated the shell of the dentaliid species Fissidentalium metivieri and Antalis weinkauffi and characterized shell crystal organization with electron backscatter diffraction (EBSD) and laser confocal and scanning electron microscopies. Based on crystal size, morphology, organization and growth-line spacing, we distinguish five different crystal arrangement motifs in the investigated shells. We find two slightly different microstructures for the shell proper, two microstructures for the attachment of muscles to the shell and one microstructure for a secondary hard tissue growth product, secreted at the apical orifice. Crystal organization motifs are crossed-lamellar, dendritic and prismatic. Crystal textures are crossed-lamellar, axial-like and crossed-lamellar-like. Crystal organization with a crossed arrangement is utilized for shell formation by representatives of many Ca-carbonate shell-secreting mollusc classes/subclasses: Scaphopoda, Gastropoda, Bivalvia, Polyplacophora (crossed-lamellar), and Patellogastropoda (crossed-foliated). Based on structural–crystallographic attributes, we highlight a basic shell structure that is broadly similar for the species of these mollusc classes/subclasses. However, this basic crystal arrangement motif is significantly modulated by the specific crystal organization that is inherent for a particular mollusc class/subclass. Full article

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

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21 pages, 2442 KB

Open AccessReview

Defect Mechanisms and Microstructural Regulation in Be–Al Alloys Across Multiple Fabrication Routes

by Geng Cao, Shaopeng Wu, Dongxin Wang, Zhaopeng Yang, Lipeng Yang and Xixi Su

Crystals 2026, 16(8), 512; https://doi.org/10.3390/cryst16080512 - 3 Aug 2026

Abstract

Be–Al alloys are attractive for aerospace and precision-engineering applications because of their low density, high specific stiffness, and excellent dimensional stability. However, their broader application is constrained by multiscale defects arising from the low mutual solubility of Be and Al, their large melting-point [...] Read more.

Be–Al alloys are attractive for aerospace and precision-engineering applications because of their low density, high specific stiffness, and excellent dimensional stability. However, their broader application is constrained by multiscale defects arising from the low mutual solubility of Be and Al, their large melting-point difference, and the high reactivity of the Be/Al interface. This review critically examines defect formation and microstructural evolution in Be–Al alloys produced by casting, powder metallurgy, pressure infiltration, thermomechanical processing, and additive manufacturing, with particular emphasis on additive manufacturing. Rapid solidification can refine the Be-rich phase and suppress coarse segregation, but unstable melt-pool behavior, restricted gas escape, cyclic thermal loading, and insufficient interfacial diffusion may also promote porosity, compositional heterogeneity, residual stress, and interfacial degradation. The mechanical properties of Be–Al alloys depend strongly on Be-phase morphology, continuity of the Al matrix, interfacial integrity, and the spatial distribution of processing-induced defects. Recent progress in alloy design, process optimization, interfacial engineering, and post-processing is evaluated, together with the limitations of the available evidence. Future research should establish quantitative processing–defect–microstructure–property relationships through in situ monitoring, multiscale characterization, predictive modeling, and standardized mechanical validation. These advances are essential for the reliable manufacture of complex, high-performance Be–Al components. Full article

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

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12 pages, 1806 KB

Open AccessArticle

W-Type Hexaferrites Made in Seconds—An In Situ Powder Diffraction Study

by Mathias Mørch, Amalie Povlsen Laursen, Jack Thomas-Hunt, Priyank Shyam and Mogens Christensen

Crystals 2026, 16(8), 511; https://doi.org/10.3390/cryst16080511 - 3 Aug 2026

Abstract

The formation of W-type hexaferrite magnets was investigated using in situ synchrotron X-ray powder diffraction. Both the holding time and precursor composition were investigated to evaluate the effect on phase purity and crystallite size using Rietveld refinements. Based on the refinements, it was [...] Read more.

The formation of W-type hexaferrite magnets was investigated using in situ synchrotron X-ray powder diffraction. Both the holding time and precursor composition were investigated to evaluate the effect on phase purity and crystallite size using Rietveld refinements. Based on the refinements, it was found that the formation of W-type hexaferrites initiates shortly after reaching 1200 °C and happens within a few seconds. M-type hexaferrite was formed at a lower temperature before being transformed into W-type hexaferrite. Despite the short holding times, at elevated temperatures, the crystallite sizes along the a,b-axis exceeded the detection limit of the powder diffraction data, as the peak widths associated with the a,b-planes became too narrow to resolve changes as function of time. Magnetization data recorded from the in situ prepared samples revealed a higher saturation magnetization in the W-type hexaferrites relative to conventional M-type hexaferrites. No appreciable coercivity was found, which can be attributed to different effects: (1) reduced anisotropy constant, (2) large crystallite growth resulting in multi-domain crystallites, or (3) exchange-coupling with soft spinel ferrite found in the sample. Based on this study, we conclude that W-type hexaferrites can be formed after a few seconds at 1200 °C and that crystallite growth happens subsequently after the formation of the W-type hexaferrite structure. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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3 pages, 148 KB

Open AccessCorrection

Correction: Ren et al. Effect of Interstitial Oxygen on the Microstructure and Mechanical Properties of Titanium Alloys: A Review. Crystals 2025, 15, 618

by Yaojia Ren, Jiajun Xu, Yingkang Wei, Yingying Liu, Jilei Zhu and Shifeng Liu

Crystals 2026, 16(8), 510; https://doi.org/10.3390/cryst16080510 - 3 Aug 2026

Abstract

Correction 1: Abbreviation error [...] Full article

10 pages, 3795 KB

Open AccessArticle

Growth of High-Quality CLBO Crystals for High-Power 266 nm DUV Laser

by Jinguo Wang, Lei Yang, Gang He and Zhanggui Hu

Crystals 2026, 16(8), 509; https://doi.org/10.3390/cryst16080509 - 3 Aug 2026

Abstract

In this work, LiF was introduced as a flux additive to overcome the high viscosity challenge of the self-flux system, which successfully grew a large-scale cesium lithium borate (CLBO) single crystal with dimensions of 136 × 132 × 68 mm³ and a [...] Read more.

In this work, LiF was introduced as a flux additive to overcome the high viscosity challenge of the self-flux system, which successfully grew a large-scale cesium lithium borate (CLBO) single crystal with dimensions of 136 × 132 × 68 mm³ and a weight of 1275 g via the top-seeded solution growth (TSSG) method. The as-grown crystal showed an optical transmittance of over 90% in the spectral range of 230–1880 nm and an extremely low absorption coefficient of 2.8 ppm/cm at 1064 nm. Notably, under 120 W pumping at a high repetition rate of 2 MHz, the fabricated CLBO optical element achieved a record-high 266 nm output power of 26.1 W with an optical conversion efficiency of 21.75%. Moreover, the laser system maintained stable continuous operation at >23 W for over 120 h. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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19 pages, 8836 KB

Open AccessArticle

Effect of Nickel Content and Cooling Rate on the Microstructure of As-Cast 316 Stainless Steels Part II: Ferrite and Precipitated Phases Under the Same Sampling Conditions

by Zhixuan Xue, Dongzhi Hou, Lei Chen, Ziyu Su, Jixiang Liang, Shanding Ma, Zhou Li, Kun Yang, Yanhui Sun and Chao Chen

Crystals 2026, 16(8), 508; https://doi.org/10.3390/cryst16080508 - 3 Aug 2026

Abstract

The presence of ferrite in 316 austenitic stainless steel affects its magnetic permeability, and the secondary precipitates formed by ferrite decomposition can further degrade the corrosion resistance, limiting its application in industries such as nuclear power and medical devices. In previous studies, the [...] Read more.

The presence of ferrite in 316 austenitic stainless steel affects its magnetic permeability, and the secondary precipitates formed by ferrite decomposition can further degrade the corrosion resistance, limiting its application in industries such as nuclear power and medical devices. In previous studies, the characteristics of ferrite and precipitates in several 316 stainless steel continuous-casting billet samples with different Ni contents were analyzed. In this work, remelting experiments were further conducted on several 316L stainless steels with different Ni contents using a tube furnace; according to the Ni content, they are designated as L-316, M-316, and H-316 stainless steels. Metallographic analysis and electron back-scattered diffraction (EBSD) characterization were employed. The effects of Ni content and cooling rate on the microstructure of 316 stainless steel were systematically investigated. The results show that for the L-316 stainless steel, the ferrite morphologies in water-cooled, oil-cooled, air-cooled, and furnace-cooled samples change successively as follows: skeletal and lath-like, clustered network, lath-like and clustered network, and short rod-like. For the M-316 stainless steel remelted samples, the ferrite morphologies are network and skeletal, network and short rod-like, semi-network and short rod-like, and semi-network, respectively. The solidification modes of the L-316, M-316, and H-316 stainless steel remelted samples are FA, FA, and AF modes, respectively. Increasing Ni content reduces the ferrite content under all cooling conditions. When the Ni content increases from 10% to 12.17%, the ferrite content decreases significantly, with a greater reduction at higher cooling rates; when the Ni content further increases to 14.25%, the decrease in ferrite content slows down, indicating that after Ni content reaches a certain level, its inhibiting effect on ferrite formation weakens. The effect of cooling rate on ferrite content depends on the solidification mode: in the FA mode, slow cooling promotes diffusional transformation of ferrite to austenite, so the ferrite content decreases with decreasing cooling rate—for L-316 stainless steel, the ferrite content drops from 22.44% in the water-cooled sample to 2.71% in the furnace-cooled sample. In the AF mode, slow cooling favors the enrichment of elements at grain boundaries and promotes ferrite nucleation and growth; the overall trend of ferrite content increases as the cooling rate decreases. For the H-316 stainless steel specimens, the ferrite content is similar between water-cooled specimens (0.36%) and oil-cooled specimens (0.26%); for air-cooled specimens, the ferrite content increases significantly to 1.49%; and finally, it reaches 1.94% for the furnace-cooled specimen. Regarding secondary precipitates, the phase constituents of the L-316 stainless steel specimens after water cooling, oil cooling, and air cooling consist of an austenite matrix and ferrite, with a secondary precipitated Chi phase forming only under furnace cooling conditions. For the M-316 stainless steel, the Sigma phase and Chi phase begin to form under oil cooling conditions, and the Sigma phase also precipitates in the oil-cooled specimens of the H-316 stainless steel. In the air-cooled and furnace-cooled specimens of both M-316 and H-316 stainless steels, the secondary precipitated phase is the Sigma phase. All three types of water-cooled stainless steel specimens exhibited no secondary precipitate phase; increasing the cooling rate suppresses atomic diffusion, thereby reducing the precipitation of Chi phase and Sigma phase; however, a higher Ni content shifts the solidification mode toward the AF mode, making secondary precipitates more prone to form. Full article

(This article belongs to the Special Issue Crystallization of High-Performance Metallic Materials (3rd Edition))

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19 pages, 2909 KB

Open AccessArticle

Vinpocetine: Polymorph and Solvate Screening Supports a Monomorphic Crystal Landscape

by Katarina Bolko-Seljak, Ilenia D’Abbrunzo and Beatrice Perissutti

Crystals 2026, 16(8), 507; https://doi.org/10.3390/cryst16080507 - 1 Aug 2026

Abstract

The solid-state landscape of pharmaceutical compounds is often characterized by the occurrence of polymorphs, hydrates, and solvates, which may significantly influence their physicochemical and biopharmaceutical properties. In contrast, some active pharmaceutical ingredients exhibit a remarkable resistance to crystal form diversification, despite extensive experimental [...] Read more.

The solid-state landscape of pharmaceutical compounds is often characterized by the occurrence of polymorphs, hydrates, and solvates, which may significantly influence their physicochemical and biopharmaceutical properties. In contrast, some active pharmaceutical ingredients exhibit a remarkable resistance to crystal form diversification, despite extensive experimental investigation. In the present work, vinpocetine was subjected to an extensive solid-form screening campaign aimed at exploring its propensity to generate alternative polymorphs, hydrates, and solvates. Mechanochemical experiments were performed under neat grinding and liquid-assisted grinding conditions using a broad range of organic solvents and water, including two-step milling procedures and formulations containing surfactants. Additional investigations included high-energy planetary milling, high-pressure compaction, exposure to controlled humidity, thermal cycling, slurry-bridging experiments in various media, and crystallization after mechanochemical neutralization of vinpocetine salts. The resulting solids were systematically characterized by powder X-ray diffraction, and thermal and morphological analyses. In all cases, the recovered solid corresponded to the commercially available crystalline form of vinpocetine, with no evidence of alternative polymorphs, solvates, or hydrates. These results demonstrate the unusual robustness of vinpocetine crystal structure across a wide range of mechanical, thermal, and solvent-mediated conditions. Notably, this behavior contrasts with the well-established ability of vinpocetine to form numerous salts and salt cocrystals, suggesting that solid-state diversification in this compound is primarily driven by proton-transfer processes rather than by neutral polymorphism or solvent incorporation. The present study provides experimentally defined boundaries for the solid-state landscape of vinpocetine and contributes valuable data for future crystal-form prediction and pharmaceutical development studies. Beyond the specific findings reported herein, the systematic documentation of both successful and unsuccessful experimental outcomes represents a valuable source of experimentally validated positive and negative data that may support the future development and validation of AI-assisted crystal-form prediction tools. Full article

(This article belongs to the Section Organic Crystalline Materials)

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16 pages, 6152 KB

Open AccessArticle

Structural Characterization, Hirshfeld Surface Analysis, Thermal Behavior and Optical Bandgap of N,N′-bis(Phosphonomethyl)pyromellitimide

by Kenya V. Medina, Juan L. Pinedo, Katia Campos, Callah Preti, Kenya Rosas, Erick Morales Orrante, Josemaria S. Soriano, Hadi D. Arman and Pius O. Adelani

Crystals 2026, 16(8), 506; https://doi.org/10.3390/cryst16080506 - 1 Aug 2026

Abstract

The condensation reaction of pyromellitic dianhydride and (aminomethyl)phosphonic acid in imidazole yielded N,N′-bis(phosphonomethyl)pyromellitimide ([(H₂O₃P)CH₂-(C₁₀H₂N₂O₄)-CH₂(PO₃H₂)]∙2H₂O). Recrystallization of this compound from deionized water, [...] Read more.

The condensation reaction of pyromellitic dianhydride and (aminomethyl)phosphonic acid in imidazole yielded N,N′-bis(phosphonomethyl)pyromellitimide ([(H₂O₃P)CH₂-(C₁₀H₂N₂O₄)-CH₂(PO₃H₂)]∙2H₂O). Recrystallization of this compound from deionized water, by placing the solution in a desiccator to allow slow diffusion of HCl, afforded suitable single crystals for X-ray crystallographic studies. The compound crystallizes in the monoclinic space group P2₁/n. The flexible methylene phosphonic acid groups appended to both nitrogen termini adopt a trans configuration. The phosphonate and carbonyl groups (acceptors: P=O and C=O), together with water molecules [donor: O(6)—H∙∙∙O], participate in an extensive network of hydrogen-bonding interactions. Two of the phosphonate groups are protonated as P—OH (donors) and interact with oxygen atoms of neighboring phosphonate groups and water molecules. Hirshfeld surface analysis and associated two-dimensional fingerprint plots indicate that O∙∙∙H/H∙∙∙O (56.1%) contacts are the primary contributors to the crystal packing, followed by H∙∙∙H (16.3%) and C∙∙∙O/O∙∙∙C (13.4%) interactions. No significant π–π interactions were observed. The direct optical bandgap value, estimated from the Tauc plot, is 3.24 eV, indicating semiconducting behavior. The compound also exhibits thermal stability up to ~270 °C. These properties suggest that this compound may be a promising candidate for future investigation in organic electronic and optoelectronic materials. Full article

(This article belongs to the Section Organic Crystalline Materials)

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