Crystals

30 pages, 3236 KB

Open AccessReview

Recent Advancements in N-polar GaN HEMT Technology

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

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

Viewed by 1294

Abstract

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

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

(This article belongs to the Section Inorganic Crystalline Materials)

► Show Figures

Figure 1

13 pages, 6397 KB

Open AccessArticle

The Influence of Pressure on Magnetite–Zinc Oxide Synthesis in Hydrothermal Conditions

by Miruna-Adriana Ioța, Laura-Mădălina Cursaru, Ioan Albert Tudor, Marian-Nicolae Costea, Alexandru Cristian Matei, Dumitru Valentin Dragut, Roxana Mioara Piticescu and Adriana-Gabriela Șchiopu

Crystals 2025, 15(9), 829; https://doi.org/10.3390/cryst15090829 - 22 Sep 2025

Viewed by 483

Abstract

The combination of ZnO and Fe₃O₄ nanoparticles represents a synergistic strategy for the treatment of skin cancer, exploiting both oxidative stress-induced cytotoxicity and hyperthermic effects for improved anticancer activity. These nanoparticles also function as drug carriers, facilitating targeted delivery and [...] Read more.

The combination of ZnO and Fe₃O₄ nanoparticles represents a synergistic strategy for the treatment of skin cancer, exploiting both oxidative stress-induced cytotoxicity and hyperthermic effects for improved anticancer activity. These nanoparticles also function as drug carriers, facilitating targeted delivery and reducing systemic toxicity. Furthermore, controlled-release systems activated by external stimuli, such as light, pH, temperature, or magnetic fields, optimize the accumulation of the drug in tumor tissues. In the present study, Fe₃O₄-ZnO composite powders were synthesized in aqueous solution through the hydrothermal method under high pressure and temperature. All synthesized powders were characterized by physicochemical and morpho-structural methods such as: FT-IR, XRD, SEM, DLS, and BET. The influence of the hydrothermal synthesis parameters (pressure and time) on the morpho-structural properties of the magnetite–zinc oxide nanocomposites was studied. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

► Show Figures

Figure 1

18 pages, 3472 KB

Open AccessArticle

Study of Neutron Absorption of Reactor Spectrum by Composites Based on UHMWPE

by Yernat A. Kozhakhmetov, Mazhyn K. Skakov, Bauyrzhan T. Tuyakbayev, Yerzhan Ye. Sapatayev and Alexandr V. Gradoboev

Crystals 2025, 15(9), 828; https://doi.org/10.3390/cryst15090828 - 20 Sep 2025

Viewed by 475

Abstract

The development of radiation-protective materials with high resistance under reactor irradiation conditions is one of the urgent tasks in modern nuclear technologies. Ultra-high molecular weight polyethylene (UHMWPE) is considered a promising matrix material due to its high hydrogen content, low density, and strong [...] Read more.

The development of radiation-protective materials with high resistance under reactor irradiation conditions is one of the urgent tasks in modern nuclear technologies. Ultra-high molecular weight polyethylene (UHMWPE) is considered a promising matrix material due to its high hydrogen content, low density, and strong chemical resistance. Composite samples were fabricated by flame formation and irradiated in the IVG-1M research reactor of the National Nuclear Center of the Republic of Kazakhstan. Their neutron absorption capacity, bending strength, and chemical resistance were measured before and after irradiation. The results show that H₃BO₃ provides the strongest contribution to the increase in the neutron absorption coefficient, with the maximum effect observed at 30% filler content. Reactor irradiation caused only a moderate reduction in the composites’ bending strength. Chemical resistance tests confirmed that UHMWPE-based composites with WC and PbO retain stability in aggressive environments, even after reactor exposure. Overall, UHMWPE-based composites containing boron and heavy-element fillers demonstrate strong potential as radiation-protective materials. Their design should account not only for neutron absorption efficiency but also for mechanical strength and chemical resistance under reactor operating conditions. Full article

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

► Show Figures

Figure 1

32 pages, 3156 KB

Open AccessArticle

Magneto-Hygrothermal Deformation of FG Nanocomposite Annular Sandwich Nanoplates with Porous Core Using the DQM

by Fatemah H. H. Al Mukahal, Mohammed Sobhy and Aamna H. K. Al-Ali

Crystals 2025, 15(9), 827; https://doi.org/10.3390/cryst15090827 - 20 Sep 2025

Viewed by 391

Abstract

This study introduces a novel numerical approach to analyze the axisymmetric bending behavior of functionally graded (FG) graphene platelet (GPL)-reinforced annular sandwich nanoplates featuring a porous core. The nanostructures are exposed to coupled magnetic and hygrothermal environments. The porosity distribution and GPL weight [...] Read more.

This study introduces a novel numerical approach to analyze the axisymmetric bending behavior of functionally graded (FG) graphene platelet (GPL)-reinforced annular sandwich nanoplates featuring a porous core. The nanostructures are exposed to coupled magnetic and hygrothermal environments. The porosity distribution and GPL weight fraction are modeled as nonlinear functions through the thickness, capturing realistic gradation effects. The governing equations are derived using the virtual displacement principle, taking into account the Lorentz force and the interaction with an elastic foundation. To address the size-dependent behavior and thickness-stretching effects, the model employs the nonlocal strain gradient theory (NSGT) integrated with a modified version of Shimpi’s quasi-3D higher-order shear deformation theory (Q3HSDT). The differential quadrature method (DQM) is applied to obtain numerical solutions for the displacement and stress fields. A detailed parametric study is conducted to investigate the influence of various physical and geometric parameters, including the nonlocal parameter, strain gradient length scale, magnetic field strength, thermal effects, foundation stiffness, core thickness, and radius-to-thickness ratio. The findings support the development of smart, lightweight, and thermally adaptive nano-electromechanical systems (NEMS) and provide valuable insights into the mechanical performance of FG-GPL sandwich nanoplates. These findings have potential applications in transducers, nanosensors, and stealth technologies designed for ultrasound and radar detection. Full article

► Show Figures

Figure 1

15 pages, 1554 KB

Open AccessArticle

Growth and Atomic-Scale Characterization of 2D Gallium Selenide Crystals via STEM and EELS

by Antonio Serra, Letizia Meleleo, Alessandro Buccolieri, Lucio Calcagnile and Daniela Manno

Crystals 2025, 15(9), 826; https://doi.org/10.3390/cryst15090826 - 20 Sep 2025

Viewed by 458

Abstract

The advent of graphene has catalyzed extensive exploration into two-dimensional (2D) materials, among which gallium selenide (GaSe)—a layered semiconductor—stands out for its promise in optoelectronic and nanoscale device applications. To elucidate the intricate correlation between structure and electronic properties, and to enable performance [...] Read more.

The advent of graphene has catalyzed extensive exploration into two-dimensional (2D) materials, among which gallium selenide (GaSe)—a layered semiconductor—stands out for its promise in optoelectronic and nanoscale device applications. To elucidate the intricate correlation between structure and electronic properties, and to enable performance optimization at the atomic scale, we employ advanced characterization methodologies. In this work, atomic-resolution Scanning Transmission Electron Microscopy (STEM) and Electron Energy Loss Spectroscopy (EELS) are utilized to investigate the structural and electronic characteristics of GaSe. STEM imaging confirms the atomic-level uniformity and verifies the β-GaSe phase, while EELS measurements reveal a thickness-dependent, tunable bandgap that decreases from 3.8 eV to 2.4 eV as the crystal thickness increases from approximately 1 nm to 30 nm—a trend attributable to quantum confinement effects. Full article

(This article belongs to the Section Crystal Engineering)

► Show Figures

Figure 1

16 pages, 3960 KB

Open AccessArticle

Microgravity-Grown Crystals as Seeds for Pharmaceutical Compounds

by Jessica Paulson, Lillian Miller, Stephen Tuma, Molly K. Mulligan, Kenneth A. Savin and Anne M. Wilson

Crystals 2025, 15(9), 825; https://doi.org/10.3390/cryst15090825 - 20 Sep 2025

Viewed by 507

Abstract

Polymorph formation of pharmaceutical agents continues to be a challenge for the industry. Using seeds to provide the desired polymorphic form is a practice that circumvents this obstacle. Crystals grown in a microgravity environment provide an optimal template for seeding additional crystallization. In [...] Read more.

Polymorph formation of pharmaceutical agents continues to be a challenge for the industry. Using seeds to provide the desired polymorphic form is a practice that circumvents this obstacle. Crystals grown in a microgravity environment provide an optimal template for seeding additional crystallization. In this study, single crystals were utilized as seeds for multiple generations of the same polymorph formation for carbamazepine and atorvastatin calcium. This study shows that microgravity can provide different polymorphs than ground studies under the same conditions and that these crystals are excellent seeds for up to 10 generations of crystal growth. Full article

(This article belongs to the Section Biomolecular Crystals)

► Show Figures

Figure 1

16 pages, 2035 KB

Open AccessArticle

Mineral Compositions and Organic Color-Related Compounds of Freshwater Bead-Cultured Pearls from Zhuji, Southeast China: Insights from Multi-Spectroscopic Analyses

by Xi Li, Xiao-Yan Yu and Cun Zhang

Crystals 2025, 15(9), 824; https://doi.org/10.3390/cryst15090824 - 20 Sep 2025

Viewed by 411

Abstract

Freshwater bead-cultured pearls (FWBCPs) from Zhuji, China, have gained significant market prominence due to their large size, unique pearl luster, and diverse color. This study systematically investigated the mineral compositions and organic color-related compounds of twelve representative freshwater cultured pearls through a multi-analytical [...] Read more.

Freshwater bead-cultured pearls (FWBCPs) from Zhuji, China, have gained significant market prominence due to their large size, unique pearl luster, and diverse color. This study systematically investigated the mineral compositions and organic color-related compounds of twelve representative freshwater cultured pearls through a multi-analytical approach integrating Fourier transform infrared spectroscopy (FTIR), Laser Raman spectroscopy (LRS), ultraviolet–visible spectroscopy (UV-Vis), cathodoluminescence (CL), micro-infrared spectroscopy, and differential thermal–thermogravimetric analysis (TGA-DTA). Key findings reveal that FWBCPs from Zhuji primarily consist of aragonite, organic matter and adsorbed water, occasionally containing vaterite. No obvious correlation was observed between the mineral compositions and the quality of the pearls. Raman spectra exhibit characteristic bands of polyenes near 1525 cm⁻¹ (attributed to the stretching vibration of C=C, ν₁) and near 1131 cm⁻¹ (attributed to the stretching vibration of C-C, ν₂). The different colors are formed by various polyenes with the exact position of the characteristic bands determined by the concentrations of C=C in the polyenes. FWBCPs and freshwater non-bead-cultured pearls (FWNBCPs) exhibit essentially the same mineral compositions and organic color-related compounds, but can be distinguished from each other based on their internal structures. These results advance the understanding of freshwater pearl formation mechanisms and establish a scientific foundation for quality evaluation in the gemological industry. Full article

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

► Show Figures

Figure 1

19 pages, 2773 KB

Open AccessArticle

Study of the System of Two Parallel Reactions—Carburization of Nanocrystalline Iron and Formation of a Carbon Deposit

by Rafał J. Pelka and Ewa A. Ekiert

Crystals 2025, 15(9), 823; https://doi.org/10.3390/cryst15090823 - 19 Sep 2025

Viewed by 380

Abstract

The reaction system of nanocrystalline iron carburization and carbon deposit formation as an example of a parallel chemical reaction was studied. The main measurement procedure was the Chemical Potential Programmed Reaction method, according to which the course of a chemical reaction in this [...] Read more.

The reaction system of nanocrystalline iron carburization and carbon deposit formation as an example of a parallel chemical reaction was studied. The main measurement procedure was the Chemical Potential Programmed Reaction method, according to which the course of a chemical reaction in this particular case was controlled by the methane–hydrogen mixtures of precisely selected variable composition. The measurements were performed in a tubular differential flow reactor with thermogravimetric measurement and analysis of the gas phase composition at a temperature of 650 °C under atmospheric pressure. In the current research, by measuring the mass of the solid sample at changing carburizing potential and after balancing the reacting system, the reaction rates of parallel iron carburization and carbon deposit formation were precisely determined using the model of the reaction of a nanocrystalline substance with the gas phase in states close to chemical equilibrium. The reaction rate constants for those reactions were estimated as well based on model equations. Full article

► Show Figures

Figure 1

14 pages, 2817 KB

Open AccessArticle

Light-Induced Heating of Microsized Nematic Volumes

by Dmitrii Shcherbinin, Denis A. Glukharev, Semyon Rudyi, Anastasiia Piven, Tetiana Orlova, Izabela Śliwa and Alex Zakharov

Crystals 2025, 15(9), 822; https://doi.org/10.3390/cryst15090822 - 19 Sep 2025

Viewed by 379

Abstract

The experimental study has been carried out using advanced computer vision methods in order to visualize the moment of excitation and further propagation of a non stationary isotropic domain in a hybrid aligned nematic (HAN) microsized volume under the effect of a laser [...] Read more.

The experimental study has been carried out using advanced computer vision methods in order to visualize the moment of excitation and further propagation of a non stationary isotropic domain in a hybrid aligned nematic (HAN) microsized volume under the effect of a laser beam focused on a bounding liquid crystal surface. It has been shown that, when the laser power exceeds a certain threshold value, in bulk of the HAN microvolume, an isotropic circular domain is formed. We also observed a structure of alternating concentric rings around the isotropic circular region, which increases with distance from the center of the isotropic domain. The formation of a sequence of rings in a polarizing microscopic image indicates the formation of a complex topology of the director field in the HAN cell under study. The following evolution of the texture can be represented by two modes. Firstly, the “fast” heating mode, which is responsible for the formation and explosive expansion of an isotropic zone in bulk of the HAN microvolume with characteristic time

τ_{1}

due to a laser spot heating on the upper indium tin oxide (ITO) layer. Secondly, the “slow” heating mode, when an isotropic zone and concentric rings slowly expand with characteristic time

τ_{2}

mainly due to the finite thermoconductivity of ITO layer. When the laser power significantly exceeds the threshold value, damped oscillations of the isotropic domain are observed. We also introduced the metrics that allows quantitatively estimate the behavior of texture observed. The results obtained form an experimental basis for further investigation of thermomechanical force appearing in the LC system with coupled gradients of temperature and director fields. Full article

(This article belongs to the Collection Liquid Crystals and Their Applications)

► Show Figures

Figure 1

13 pages, 4818 KB

Open AccessArticle

Structural Characteristics of Homoleptic Zinc Complexes Incorporating Asymmetric Aminopyridinates

by Awal Noor and Sadaf Qayyum

Crystals 2025, 15(9), 821; https://doi.org/10.3390/cryst15090821 - 19 Sep 2025

Viewed by 378

Abstract

First examples of mononuclear homoleptic zinc aminopyridinates have been isolated by reacting the sterically bulky deprotonated 2-aminopyridine ligands, N-(2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)-pyridine-2-yl]-amine (1) and N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridine-2-yl]-amine (2) with [Zn{N(SiMe₃)₂}₂]. Single crystal X-ray analyses of the zinc bis(aminopyridinate) [...] Read more.

First examples of mononuclear homoleptic zinc aminopyridinates have been isolated by reacting the sterically bulky deprotonated 2-aminopyridine ligands, N-(2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)-pyridine-2-yl]-amine (1) and N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridine-2-yl]-amine (2) with [Zn{N(SiMe₃)₂}₂]. Single crystal X-ray analyses of the zinc bis(aminopyridinate) complexes (3 and 4) reveal two different orientations of the coordinated ligands most probably due to the steric variation of the of the applied ligands. For 3 not only the two ligands show rare head to head arrangement but also one of the ligand exhibit localized and the other ligand delocalized mode of coordination. In 4 the two ligands adopt the head to tail arrangement for the two coordinated aminopyridinato ligands with anionic function localized at the amido nitrogen atom of both the ligands. NMR tube reactions between equimolar ratios of 1 or 2 and [Zn{N(SiMe₃)₂}₂] show the possible synthesis of the mono(aminopyridnate) Zn amide complexes (5 and 6, respectively) in solution phase, however, the corresponding bis(aminopyridinate) Zn complexes are the selective products. Hirshfeld surface analysis and the two-dimensional fingerprint plots indicate that intermolecular H⋯H contacts and H⋯C/C⋯H π-interactions dominate the crystal packing. Full article

(This article belongs to the Section Crystal Engineering)

► Show Figures

Figure 1

17 pages, 8210 KB

Open AccessArticle

BGO@ZnO Heterostructures for Ultrafast Scintillation Detectors

by Nataliya Babayevska, Mariusz Jancelewicz, Igor Iatsunskyi, Marcin Jarek, Ivan Yakymenko, Aravinthkumar Padmanaban, Oleh Viahin, Giulia Terragni, Carsten Lowis, Etiennette Auffray and Oleg Sidletskiy

Crystals 2025, 15(9), 820; https://doi.org/10.3390/cryst15090820 - 19 Sep 2025

Viewed by 394

Abstract

Developing detectors to enhance the timing resolution of positron emission tomography scanners can help reduce radioactive doses absorbed by patients and improve spatial resolution in medical imaging. Time resolution may be enhanced in heterostructures comprising a heavy scintillator for attenuation of 511 keV [...] Read more.

Developing detectors to enhance the timing resolution of positron emission tomography scanners can help reduce radioactive doses absorbed by patients and improve spatial resolution in medical imaging. Time resolution may be enhanced in heterostructures comprising a heavy scintillator for attenuation of 511 keV γ-quanta, as well as a fast scintillator converting recoiled electrons from the heavy scintillator to prompt light photons. In this study, ZnO films as fast scintillators with different thicknesses were obtained on substrates of a heavy bismuth germanate (Bi₄Ge₃O₁₂, BGO) scintillator using several film preparation techniques, such as spray-coating, drop-casting, and spin-coating. The design of heterostructures combined the key advantage of a low-cost film preparation technique with environmentally friendly and available precursors. This work proposes synthesis methods of highly nanocrystalline ZnO films on BGO, where a film thickness ranges from 6 to 18 μm. All ZnO studied films exhibit exciton luminescence peaked in UV (353 nm) and defect luminescence in the green (657 nm) range under 325 nm excitation. The best coincidence time resolution of 158 ± 8 ps was obtained with BGO@ZnO heterostructures fabricated by the spray-coating. The proposed approach allowed obtaining BGO@ZnO heterostructures for potential use as ultrafast scintillation detectors. Full article

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

► Show Figures

Figure 1

16 pages, 12574 KB

Open AccessArticle

Enhanced Performance of Gold Nanoparticle-Modified Nickel–Iron Coatings for Sodium Borohydride Electrooxidation

by Huma Amber, Aušrinė Zabielaitė, Aldona Balčiūnaitė, Antanas Nacys, Dmytro Shyshkin, Birutė Šimkūnaitė-Stanynienė, Zenius Mockus, Jūratė Vaičiūnienė, Loreta Tamašauskaitė-Tamašiūnaitė and Eugenijus Norkus

Crystals 2025, 15(9), 819; https://doi.org/10.3390/cryst15090819 - 19 Sep 2025

Viewed by 403

Abstract

The Ni-Fe coatings modified with AuNPs were deposited on the flexible copper-coated polyimide (Cu/PI) surface using electroless metal plating, while the galvanic displacement technique was applied to modify the surface of NiFe coatings by a small content of AuNPs in the range of [...] Read more.

The Ni-Fe coatings modified with AuNPs were deposited on the flexible copper-coated polyimide (Cu/PI) surface using electroless metal plating, while the galvanic displacement technique was applied to modify the surface of NiFe coatings by a small content of AuNPs in the range of 16.5 µg_Au cm⁻². AuNPs of a few nanometers in size were deposited on the NiFe/Cu/PI surface by immersing it in a solution containing AuCl₄⁻ ions. The electrooxidation of sodium borohydride was evaluated in a 1 M NaOH solution containing 0.05 M of sodium borohydride using cyclic voltammetry, chronoamperometry, and chronopotentiometry. In addition, the performance and stability of the NiFe/Cu/PI and AuNPs-NiFe/Cu/PI catalysts were evaluated for potential use in a direct NaBH₄-H₂O₂ fuel cell. The NiFe coating modified with AuNPs demonstrated significantly higher electrocatalytic activity towards the oxidation of sodium borohydride as compared to bare Au or unmodified NiFe/Cu/PI. Furthermore, it exhibited a superior power density of 89.7 mW cm⁻² at room temperature and operational stability under alkaline conditions, while the NiFe anode exhibited 73.1 mW cm⁻². These results suggest that the AuNPs-modified NiFe coating has great potential as a material for use in direct borohydride fuel cells (DBFCs) applications involving the oxidation of sodium borohydride. Full article

(This article belongs to the Special Issue Advances and Perspectives in Noble Metal Nanoparticles)

► Show Figures

Figure 1

13 pages, 1021 KB

Open AccessArticle

Fractional Conductances of Wires: The S-Matrix Approach

by Rose Davies, Victor Kagalovsky and Igor V. Yurkevich

Crystals 2025, 15(9), 818; https://doi.org/10.3390/cryst15090818 - 18 Sep 2025

Viewed by 270

Abstract

Quasi-one-dimensional systems with multiple conduction channels are essential for describing a range of physical phenomena. In this paper, we analyse transport in wires where electrons are subject to arbitrary number of strong multi-particle backscattering terms. We present an exact calculation of the system’s [...] Read more.

Quasi-one-dimensional systems with multiple conduction channels are essential for describing a range of physical phenomena. In this paper, we analyse transport in wires where electrons are subject to arbitrary number of strong multi-particle backscattering terms. We present an exact calculation of the system’s scattering matrix and derive a formula for the two-terminal conductance. We find the conductance is reduced from its ideal value by a term corresponding to the projection of current fields onto the subspace of integer-valued vectors characterising the gapped channels created by the perturbations. Applying this result, we establish the minimal model required to reproduce the recently observed, yet unexplained, fractional conductance plateaus with even denominators. Full article

► Show Figures

Figure 1

19 pages, 7172 KB

Open AccessArticle

Colorimetric Properties and Classification of “Tang yu”

by Kaichao Liu, Jun Tang and Ying Guo

Crystals 2025, 15(9), 817; https://doi.org/10.3390/cryst15090817 - 18 Sep 2025

Viewed by 385

Abstract

This study quantitatively analyses how light sources, polishing methods, and backgrounds affect the color of “Tang yu”. Twenty-four samples were tested with three different light sources (D50, A, D65), two polishing methods, and nine Munsell neutral gray backgrounds. Testing 24 samples revealed that [...] Read more.

This study quantitatively analyses how light sources, polishing methods, and backgrounds affect the color of “Tang yu”. Twenty-four samples were tested with three different light sources (D50, A, D65), two polishing methods, and nine Munsell neutral gray backgrounds. Testing 24 samples revealed that main coloring elements exhibit low concentrations with no linear relationship to color intensity. Light sources selectively alter chromaticity: D65 maintains color balance (recommended for grading), while A enhances red tones. Polishing methods significantly impact color perception, with glassy polishing markedly increasing Lightness (L*↑11.41%) and Chroma (C*↑42.11%) while shifting hues toward red-yellow. Background luminance (γ_b) critically influences color results: Lightness L* and Chroma C* increase via distinct power functions as γ_b rises, though Hue angle (h°) remains stable. Sample color can be predicted through γ_b based equations, with Munsell N9 background proving optimal for grading. Cluster and discriminant analyses effectively classified colors into three distinct groups, establishing a foundation for a reliable grading system. Full article

(This article belongs to the Collection Topic Collection: Mineralogical Crystallography)

► Show Figures

Figure 1

15 pages, 4652 KB

Open AccessArticle

All MOVPE Grown Quadruple Junction InGaP/InGaAs/Ge/Ge Solar Cell

by Gianluca Timò, Marco Calicchio, Elisabetta Achilli, Nicola Armani, Filippo Annoni, Franco Trespidi, Mario V. Imperatore, Edoardo Celi and Alessandro Minuto

Crystals 2025, 15(9), 816; https://doi.org/10.3390/cryst15090816 - 18 Sep 2025

Viewed by 303

Abstract

Most commercially available InGaP/InGaAs/Ge triple-junction solar cells suffer from current mismatch due to the excess current generated by the Ge sub-cell. Combining epitaxial germanium with III–V materials would enable the realization of lattice-matched four- or five-junction solar cells, where the near-infrared spectrum could [...] Read more.

Most commercially available InGaP/InGaAs/Ge triple-junction solar cells suffer from current mismatch due to the excess current generated by the Ge sub-cell. Combining epitaxial germanium with III–V materials would enable the realization of lattice-matched four- or five-junction solar cells, where the near-infrared spectrum could be split between two Ge sub-cells instead of one, thereby eliminating current mismatch in these devices and achieving higher conversion efficiency. In this work, we present the first demonstration of a quadruple-junction (4J) InGaP/InGaAs/Ge/Ge device, with all layers sequentially deposited in the same MOVPE growth chamber. The 4J device also features a novel architecture that exploits the “transistor effect” between the two Ge junctions to eliminate the current mismatch in the upper 3J InGaP/GaAs/Ge part. We describe the growth and the cell structure realization strategy developed to overcome—and, where beneficial, to exploit—the cross-contamination between III–V and group IV elements, thus avoiding the need for two separate deposition systems. The structural and electrical characterizations performed to ascertain the 4J device quality are presented. This result represents a key step toward the realization of highly efficient, all-MOVPE-grown, lattice-matched MJ solar structures that combine III–V and group IV alloys. Full article

(This article belongs to the Special Issue Crystal Growth of III–V Semiconductors)

► Show Figures

Figure 1

20 pages, 7801 KB

Open AccessArticle

Microstructure and Mechanical Property of Thin-Walled Inconel 718 Parts Fabricated by Ultrasonic-Assisted Laser-Directed Energy Deposition

by Bo Peng, Xiaoqiang Zhang, Mengmeng Zhang, Ze Chai, Fahai Ba and Xiaoqi Chen

Crystals 2025, 15(9), 815; https://doi.org/10.3390/cryst15090815 - 18 Sep 2025

Viewed by 537

Abstract

Laser-directed energy deposition (DED) offers significant potential for the additive manufacturing of thin-walled Inconel 718 aerospace components. However, the structural defects readily formed during deposition, along with the extensive precipitation of long-chain Laves phases between coarse dendrites, can severely compromise the mechanical properties [...] Read more.

Laser-directed energy deposition (DED) offers significant potential for the additive manufacturing of thin-walled Inconel 718 aerospace components. However, the structural defects readily formed during deposition, along with the extensive precipitation of long-chain Laves phases between coarse dendrites, can severely compromise the mechanical properties of as-fabricated Inconel 718 parts. To address this, an ultrasonic-assisted DED (UDED) method was employed to reduce the deposited structural defects and refine crystalline structures, and the influences of ultrasonic energy fields on the microstructure and mechanical properties of thin-walled Inconel 718 samples were systematically investigated. The results demonstrated that ultrasonic vibration significantly enhances the microstructural quality by reducing porosity and pore size, weakening texture intensity, fragmenting long-chain Laves phases, mitigating severe elemental segregation, and refining matrix grains. Consequently, the UDED thin-walled Inconel 718 sample exhibited an approximately 15% increase in microhardness compared to the conventional DED counterpart, alongside satisfactory strength and ductility. This study highlights the superiority of UDED for microstructure tailoring and its potential for mechanical property regulations in thin-walled Inconel 718 aerospace components. Full article

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

► Show Figures

Figure 1

19 pages, 4373 KB

Open AccessArticle

Polydianiline (PDANI) from a Safe Precursor: Dopant-Driven Control of Structure and Electroactivity

by Rocco Carcione, Emanuela Tamburri, Giorgio Scordo, Francesca Pescosolido, Luca Montaina, Elena Palmieri, Alessia Cemmi and Silvia Battistoni

Crystals 2025, 15(9), 814; https://doi.org/10.3390/cryst15090814 - 17 Sep 2025

Cited by 1 | Viewed by 500

Abstract

This work focuses on the synthesis and the comprehensive characterization of polydianiline (PDANI) polymer, obtained via oxidative polymerization of dianiline, a low-toxicity and more environmentally friendly starting monomer for polyaniline (PANI) formation. Despite the structural similarity to PANI, PDANI remains underexplored, especially regarding [...] Read more.

This work focuses on the synthesis and the comprehensive characterization of polydianiline (PDANI) polymer, obtained via oxidative polymerization of dianiline, a low-toxicity and more environmentally friendly starting monomer for polyaniline (PANI) formation. Despite the structural similarity to PANI, PDANI remains underexplored, especially regarding the effect of different synthesis conditions. Here, we investigate how chloride, sulfate, and camphor sulfonate dopants, combined with green solvents such as water and DMSO, modulate the final properties of PDANI in the emeraldine salt configuration. The produced materials were extensively characterized using a multi-technique approach. FTIR, Raman, EPR, and UV-Vis spectroscopies provided insights into chemical structure, molecular order, and polaron population. Electrical conductivity was disclosed via current-voltage (I-V) measurements, while cyclic voltammetry (CV) and coulovoltammetry (QV) were employed to evaluate redox activity and charge reversibility. The resulting PDANI displays structural and functional features comparable to those of PANI synthesized under similar conditions. Notably, the nature of the dopant and acidic medium was found to crucially govern the oxidation level, molecular organization, and electrochemical performance, boosting PDANI as a tunable and sustainable alternative for applications ranging from electronics to energy storage. Full article

(This article belongs to the Special Issue Synthesis, Characterization and Applications of Crystalline Electroconductive Polymers)

► Show Figures

Figure 1

11 pages, 2594 KB

Open AccessArticle

Glass Fiber Post Pretreated with Neodymium-Doped Yttrium Orthovanadate, Toluidine Blue Activated Low-Level Laser Therapy, and Bioactive Glass: An In Vitro Analysis of SEM, Bond Strength, and Surface Roughness

by Mohammad H. AlRefeai and Fahad Alkhudhairy

Crystals 2025, 15(9), 813; https://doi.org/10.3390/cryst15090813 - 17 Sep 2025

Viewed by 401

Abstract

To evaluate the impact of different surface treatment regimens, Neodymium-doped yttrium orthovanadate (Nd: YVO4) laser, Toluidine blue (TB) activated Low-level laser therapy (LLLT), and Bioactive glass particles (BAGPs) on the surface roughness (Ra), surface morphology, and bond strength (BS) of Glass fiber posts [...] Read more.

To evaluate the impact of different surface treatment regimens, Neodymium-doped yttrium orthovanadate (Nd: YVO4) laser, Toluidine blue (TB) activated Low-level laser therapy (LLLT), and Bioactive glass particles (BAGPs) on the surface roughness (Ra), surface morphology, and bond strength (BS) of Glass fiber posts (GFP) bonded to canal dentin. Forty single human rooted incisors with a closed apex were included. The endodontic treatment was performed, followed by post space preparation. Fifty-six GFP were sorted into four categories based on the conditioning method used (n = 14). Group 1: H₂O₂, Group 2: Nd: YVO4 laser, Group 3: TB-LLLT, and Group 4: BAGPs. Surface Ra and topographic changes were identified using a profilometer and Scanning Electron Microscopy (SEM). Post cementation was executed by utilizing self-adhesive resin cement. Analysis of BS and fracture pattern was performed using a universal testing machine and a stereomicroscope, respectively. Variance analysis with Tukey’s test was used to compare Ra and BS between the study groups at different root sections (p < 0.05). Group 2 (Nd: YVO4 laser) displayed the highest Ra scores (1051.54 ± 0.087 µm) and BS at all thirds. Whereas Group 3 TB-activated LLLT exhibited the lowest outcomes of Ra (539.39 ± 0.091) and BS at all three sections. Comparison among the investigated groups displayed that Group 1 (H₂O₂) and Group 2 Nd: YVO₄ exhibited comparable outcomes of Ra and BS (p ˃ 0.05). Nd: YVO₄ laser has the potential to roughen the surface of GFP, thereby enhancing its BS to resin cement Full article

(This article belongs to the Section Inorganic Crystalline Materials)

► Show Figures

Figure 1

15 pages, 4326 KB

Open AccessArticle

Crystallographic Characterization of Different Forms of the Salt of Pazufloxacin Mesylate

by Ekaterina D. Tselukovskaya, Petr A. Buikin, Alexander S. Goloveshkin, Pavel V. Dorovatovskii and Anna V. Vologzhanina

Crystals 2025, 15(9), 812; https://doi.org/10.3390/cryst15090812 - 16 Sep 2025

Viewed by 457

Abstract

Pazufloxacin is a fluoroquinolone antibiotic synthesized by Toyama Chemical Co., Ltd. (Tokyo, Japan) in the 1990s. Up until now, the X-ray crystal structure of its mesylate salt had not been determined. The dissolution and recrystallization of pazufloxacin mesylate from different solvents afforded the [...] Read more.

Pazufloxacin is a fluoroquinolone antibiotic synthesized by Toyama Chemical Co., Ltd. (Tokyo, Japan) in the 1990s. Up until now, the X-ray crystal structure of its mesylate salt had not been determined. The dissolution and recrystallization of pazufloxacin mesylate from different solvents afforded the salts pazufloxacinium mesylate (1), pazufloxacinium mesylate dihydrate (2), pazufloxacinium mesylate hydrate (3) and pazufloxacinium mesylate bis(peroxosolvate) (4), which were all crystallographically characterized. Molecular and crystal structures of these compounds, as well as their thermal behavior, were studied. For all compounds, single-crystal X-ray diffraction confirmed that a proton migrates from methanesulfonic acid to the amino group of pazufloxacin to form a salt. Dehydration of two hydrates occurs as a two-step single-crystal-to-powder process, leading to the formation of two metastable polymorphs of the anhydrous salt. In the solid state, the peroxosolvate compound is stable under ambient conditions for several months, thus making this drug–drug solid suitable for topical application. Full article

(This article belongs to the Special Issue Structural Studies in Drug Discovery and Development: From the Lead to the Pharmaceutical Form, 2nd Edition)

► Show Figures

Figure 1

16 pages, 5392 KB

Open AccessArticle

Micro-Arc Coatings with Different Types of Microparticles on Titanium Alloy: Formation, Structure, and Properties

by Anna V. Ugodchikova, Tatiana V. Tolkacheva, Pavel V. Uvarkin, Margarita A. Khimich, Yurii P. Sharkeev, Alexander D. Kashin, Ivan A. Glukhov and Mariya B. Sedelnikova

Crystals 2025, 15(9), 811; https://doi.org/10.3390/cryst15090811 - 16 Sep 2025

Viewed by 437

Abstract

This study examines the effects of electrolyte composition, specifically the incorporation of dispersed particles, on the properties and formation kinetics of micro-arc oxidation (MAO) coatings on a bioinert titanium alloy. Coatings with particles of β-tricalcium phosphate (CP), wollastonite (CS), and combined coatings containing [...] Read more.

This study examines the effects of electrolyte composition, specifically the incorporation of dispersed particles, on the properties and formation kinetics of micro-arc oxidation (MAO) coatings on a bioinert titanium alloy. Coatings with particles of β-tricalcium phosphate (CP), wollastonite (CS), and combined coatings containing both types of particles (SP) were obtained. The MAO process was carried out using a Micro-Arc 3.0 unit in pulsed potentiostatic anode mode, with the process voltage ranging from 350 to 500 volts. The surface morphology and internal structure of the coatings were examined using scanning electron microscopy. The elemental composition of the coatings was determined by the EDX method, while the phase composition and fine structure of the coatings were investigated by XRD and TEM methods, respectively. The adhesion properties of the coatings were determined by means of scratch testing. When the MAO process voltage was increased to 500 V, the thickness of CP, CS, and SP coatings increased to 80, 50, and 50 μm, respectively. Notably, SP coatings demonstrated the highest adhesion strength (critical load L_c = 22 N), indicating their potential for use in load-bearing medical implants, where preventing delamination under mechanical stress is critical. Full article

(This article belongs to the Special Issue Development of Light Alloys and Their Applications)

► Show Figures

Figure 1

17 pages, 4863 KB

Open AccessArticle

Analysis of High Temperature Oxidation Process and Mechanism of Heterogeneous Titanium Alloy

by Xu Pei, Jiacheng Wu, Zhaomei Xu and Pengfei Li

Crystals 2025, 15(9), 810; https://doi.org/10.3390/cryst15090810 - 15 Sep 2025

Viewed by 804

Abstract

This study explores the differences in oxidation color, oxidation products, and high-temperature oxidation resistance between TA1 and Ti-6Al-4V (TC4) titanium alloys following a 50 h oxidation treatment at 450 °C and 750 °C. A combination of analytical techniques—optical microscopy, scanning electron microscopy (SEM), [...] Read more.

This study explores the differences in oxidation color, oxidation products, and high-temperature oxidation resistance between TA1 and Ti-6Al-4V (TC4) titanium alloys following a 50 h oxidation treatment at 450 °C and 750 °C. A combination of analytical techniques—optical microscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and micro-Vickers hardness testing—was employed to characterize the morphology of the oxide layers, elemental distribution, phase composition, and microhardness variations. The results reveal that at 450 °C, both alloys develop relatively compact oxide films. TA1 exhibits a yellow–gray coloration, while TC4 displays a characteristic blue–violet interwoven color. At 750 °C, however, the oxide layers become porous and prone to spallation, with a brown appearance and predominance of TiO₂. XPS analysis confirms that Ti⁴⁺ (TiO₂) is the dominant oxidation state on both alloy surfaces at 750 °C, with TC4 showing a significantly higher content of Al₂O₃. Microhardness measurements indicate that high-temperature oxidation increases the hardness of both alloys, with TC4 consistently exhibiting higher hardness than TA1. TC4 demonstrates superior oxidation resistance: at 450 °C, it forms a denser oxide layer with lower oxygen uptake, while at 750 °C, its oxide layer thickens more significantly, likely due to increased brittleness and spallation. This study underscores the profound impact of high-temperature oxidation on the microstructure and mechanical properties of titanium alloys and highlights the critical role of oxide layer density and stability in determining oxidation resistance. These findings provide valuable insights for the application of TA1 and Ti-6Al-4V alloys in high-temperature environments. Full article

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

► Show Figures

Figure 1

14 pages, 3099 KB

Open AccessArticle

Study on the Microstructure and Wear Properties of Al₂O₃-3%TiO₂-xAl Composite Coatings Prepared by Plasma Spraying

by Pengyu Dai, Yu Zhang, Xin Wang, Jiahang Yan, Lin Zhao and Xiaohong Yi

Crystals 2025, 15(9), 809; https://doi.org/10.3390/cryst15090809 - 15 Sep 2025

Viewed by 426

Abstract

Al₂O₃-3% TiO₂-xAl (x = 0, 20, 40, 60 wt.%) composite coatings were prepared on Q235 substrate by plasma spraying technology, and the effects of pure Al phase addition on the microstructure and wear properties of the coatings [...] Read more.

Al₂O₃-3% TiO₂-xAl (x = 0, 20, 40, 60 wt.%) composite coatings were prepared on Q235 substrate by plasma spraying technology, and the effects of pure Al phase addition on the microstructure and wear properties of the coatings were compared and analyzed. The results show that a unique splash-like structure was formed on the surface of the coating, and this structure became more obvious with the increase in Al content. Cross-sectional analysis shows that the introduction of pure Al phase reduces the large pores and cracks in the coating, forming a slender band structure. XRD analysis shows that the addition of pure Al phase leads to a decrease in the diffraction peak intensity of α-Al₂O₃, while the diffraction peak intensity of Al phase and γ-Al₂O₃ gradually increases, especially in the coating with 40% Al content; the diffraction peak of γ-Al₂O₃ increases significantly. XPS analysis further confirms that with the increase in Al content, a new pure Al peak appears in the Al element spectrum, and the peaks of α-Al₂O₃ and γ-Al₂O₃ fluctuate. In addition, the porosity of the coating decreases first and then increases and then decreases again with the increase in Al content. The porosity of the coating with 60% Al content is the lowest, at only 5.14%. Microhardness test results show that with the increase in Al content, the microhardness of the coating gradually decreases, and the fracture morphology changes from brittle fracture to irregular fracture, with the appearance of pull-out areas, indicating that the pure Al phase effectively improves the brittleness of the coating. However, the friction and wear test results show that the friction coefficient of the coating increases with the increase in Al content. The pure Al₂O₃ coating has high hardness and excellent wear resistance, while the coating with 60% Al content has the highest friction coefficient and the most severe wear. Moreover, adhesive wear phenomena appear on the coating surface with high Al content. Full article

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

► Show Figures

Figure 1

16 pages, 1864 KB

Open AccessArticle

Influence of Temperature on the Structural Evolution of Iron–Manganese Oxide Nanoparticles in the Hydrothermal Method

by Oscar Eduardo Cigarroa-Mayorga, Indira Torres-Sandoval, María del Rosario Munguía-Fuentes and Yazmín Mariela Hernández-Rodríguez

Crystals 2025, 15(9), 808; https://doi.org/10.3390/cryst15090808 - 13 Sep 2025

Viewed by 469

Abstract

This study is focused on the hydrothermal synthesis of iron–manganese oxide nanostructures, focusing on the influence of Fe:Mn precursor ratios, temperature, and reaction time on phase formation, morphology, and structural characteristics. Three molar ratios (Fe:Mn = 2:1, 1:1, and 1:2) were explored under [...] Read more.

This study is focused on the hydrothermal synthesis of iron–manganese oxide nanostructures, focusing on the influence of Fe:Mn precursor ratios, temperature, and reaction time on phase formation, morphology, and structural characteristics. Three molar ratios (Fe:Mn = 2:1, 1:1, and 1:2) were explored under variable conditions (80 °C, 120 °C, and 200 °C; 4, 12, and 24 h). X-ray diffraction (XRD) analysis revealed distinct phase selectivity depending on precursor composition: FeMn₂O₄ was obtained with 1:2 ratio, Fe₃Mn₃O₈ with 1:1, and Fe₂MnO₄ with 2:1, each without phase mixing. Scanning electron microscopy (FESEM) showed a pronounced effect of temperature and time on nanoparticle morphology, ranging from compact agglomerates to well-defined rod-like structures at 200 °C/24 h. Dynamic light scattering (DLS) indicated narrow size distributions for samples synthesized at 120 °C/12 h, with hydrodynamic diameters between 20 and 50 nm. Raman spectroscopy confirmed the presence of characteristic vibrational modes of spinel-type structures and validated structural integrity. High-resolution transmission electron microscopy (HRTEM) evidenced well-ordered lattice fringes with interplanar spacings of ~0.48–0.52 nm, consistent with spinel phases and indicative of high crystallinity. These findings demonstrate that controlled atomic binding and thermal parameters enable selective synthesis of pure iron–manganese oxide phases with tailored morphologies, offering a scalable route for designing advanced functional materials in catalysis, energy, and biomedical applications. Full article

(This article belongs to the Special Issue Metal Oxide-Based Nanomaterials: Advances in Synthesis, Characterization, and Applications)

► Show Figures

Figure 1

35 pages, 2008 KB

Open AccessReview

Isosymmetric Phase Transitions in Crystals: From Subtle Rearrangements to Functional Properties

by Anna Maria Mazurek, Monika Franczak-Rogowska and Łukasz Szeleszczuk

Crystals 2025, 15(9), 807; https://doi.org/10.3390/cryst15090807 - 13 Sep 2025

Viewed by 374

Abstract

Isosymmetric phase transitions (IPTs) represent a rare class of solid-state transformations in which substantial structural reorganization occurs without a change in crystallographic symmetry. These phenomena, though subtle, can have a profound impact on the physical and functional properties of materials, offering novel opportunities [...] Read more.

Isosymmetric phase transitions (IPTs) represent a rare class of solid-state transformations in which substantial structural reorganization occurs without a change in crystallographic symmetry. These phenomena, though subtle, can have a profound impact on the physical and functional properties of materials, offering novel opportunities for property tuning without chemical modification. This review provides a comprehensive overview of the experimental and computational methods used to detect and characterize IPTs, including single-crystal and powder X-ray diffraction, Raman and FT-IR spectroscopy, differential scanning calorimetry, and advanced simulation techniques such as density functional theory, molecular dynamics, and crystal structure prediction. Special emphasis is placed on correlating local structural rearrangements—such as hydrogen-bond reconfiguration, polyhedral tilting, and molecular fragment reorientation—with macroscopic thermodynamic signatures. A broad selection of examples from the literature is discussed, covering molecular crystals, coordination compounds, organic functional materials, simple salts, and inorganic oxides, with detailed tables summarizing pressure- and temperature-induced IPTs. The review also analyses the primary factors that trigger IPTs, particularly temperature and pressure, and examines their role in governing structural stability and transformation pathways. By combining structural, spectroscopic, and thermodynamic perspectives, this work aims to consolidate the understanding of IPT mechanisms and to highlight their significance for the design of responsive crystalline materials. Full article

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

► Show Figures

Figure 1

17 pages, 5216 KB

Open AccessArticle

Structural Characterization of Single-Crystalline Cored Turbine Blade Airfoils

by Jacek Krawczyk and Kamil Gancarczyk

Crystals 2025, 15(9), 806; https://doi.org/10.3390/cryst15090806 - 13 Sep 2025

Viewed by 511

Abstract

Turbine blades are the most critical parts of aircraft engines. They are exposed to complex forces at the highest temperature and an aggressive environment. For this reason, the highest demands are placed on their structural quality. In single-crystalline nickel-based superalloy blades, the quality [...] Read more.

Turbine blades are the most critical parts of aircraft engines. They are exposed to complex forces at the highest temperature and an aggressive environment. For this reason, the highest demands are placed on their structural quality. In single-crystalline nickel-based superalloy blades, the quality of the dendritic structure, crystal orientation, and local lattice parameter homogeneity is important because such properties affect the strength properties of the casting. For this reason, the structural attributes mentioned above were studied for novel, model-cored blades made of Ni-based superalloy. The blades were studied using scanning electron microscopy, the dedicated original X-ray Ω-scan method, the Laue diffraction, and the X-ray diffraction topography. The differences in the dendrites’ morphology and their array, revealing changes in dendrites’ arm size and arrangement, and changes in dendrites’ symmetry, were observed. Misoriented areas were identified, forming subgrains separated by low-angle boundaries. The location of the subgrains concerning the blade geometry and reasons for their creation were analyzed. The relation between the observed local changes in the lattice parameter and the creation of structural defects was determined. Aspects influencing the formation of structural defects that may reduce the durability of castings in specific areas of the cored blade airfoils have been discussed. Full article

(This article belongs to the Special Issue Emerging Topics of High-Performance Alloys (2nd Edition))

► Show Figures

Figure 1

14 pages, 4300 KB

Open AccessArticle

Supramolecular Stabilisation Leads to Challenging Coordination in Fe(III) Hydrazinylpyrazine Schiff Base Complexes

by Omar Coughlin, Sophie L. Benjamin and Anthony J. Fitzpatrick

Crystals 2025, 15(9), 805; https://doi.org/10.3390/cryst15090805 - 12 Sep 2025

Viewed by 417

Abstract

The coordination chemistry of a hydrazinylpyrazine-derived Schiff base ligand (L1), formed in situ from salicylaldehyde and 2-hydrazinopyrazine, with Fe(III) salts has been systematically investigated under varied synthetic conditions. Six discrete Fe(III) complexes (1a–1e and 2) were isolated and structurally [...] Read more.

The coordination chemistry of a hydrazinylpyrazine-derived Schiff base ligand (L1), formed in situ from salicylaldehyde and 2-hydrazinopyrazine, with Fe(III) salts has been systematically investigated under varied synthetic conditions. Six discrete Fe(III) complexes (1a–1e and 2) were isolated and structurally characterised via single-crystal X-ray diffraction, revealing diverse coordination geometries ranging from five-coordinate pseudo-trigonal bipyramidal to six-coordinate pseudo-octahedral environments. The supramolecular architectures are governed by a rich interplay of non-covalent interactions, including hydrogen bonding, halogen bonding, and π–π stacking, which significantly influence the crystallisation pathways and final solid-state structures. Continuous shape measure (CShM) analysis highlights substantial geometric distortion in the bis-tridentate complexes, attributed to the steric and electronic constraints imposed by the ligand. Powder X-ray diffraction and infrared spectroscopy confirm the presence of multiple phases in bulk samples, underscoring the kinetic competition between crystallisation and coordination. The results demonstrate that supramolecular stabilisation of monoligated species can kinetically inhibit bis-ligation, with ligand excess and solvent polarity serving as key parameters to direct complex speciation. These findings provide insight into the delicate balance between coordination geometry, ligand strain, and supramolecular assembly in Fe(III) Schiff base complexes. Full article

(This article belongs to the Section Crystal Engineering)

► Show Figures

Figure 1

16 pages, 10863 KB

Open AccessArticle

Pinless Friction Stir Spot Welding of Pure Copper: Process, Microstructure, and Mechanical Properties

by Xu Zhang, Xiaole Ge, Igor Kolupaev, Zhuangzhuang Shan and Hongfeng Wang

Crystals 2025, 15(9), 804; https://doi.org/10.3390/cryst15090804 - 12 Sep 2025

Viewed by 401

Abstract

Pure copper joints (PCJs) were fabricated using pinless friction stir spot welding (P-FSSW), a solid-state welding technique, to investigate the influence of plunge depth, rotational speed, and dwell time on PCJ performance. Thermal cycles under different welding parameters were recorded, while the microstructure [...] Read more.

Pure copper joints (PCJs) were fabricated using pinless friction stir spot welding (P-FSSW), a solid-state welding technique, to investigate the influence of plunge depth, rotational speed, and dwell time on PCJ performance. Thermal cycles under different welding parameters were recorded, while the microstructure at various locations within the welded zone was characterized using electron backscatter diffraction (EBSD). The microhardness and tensile–shear force (T-SF) of the PCJs were evaluated, and the fracture types together with fracture evolution were analyzed. The experimental results reveal that, under the combined effect of thermal cycles and mechanical stirring, subgrains in the welded zone transformed into recrystallized grains, whereas intense material flow contributed to an increased fraction of deformed grains. At the Hook region and the interface between the upper and lower sheets, grains were tightly bonded, resulting in effective metallurgical joining. Higher microhardness values were observed in the stir zone (SZ), whereas lower values appeared in the heat-affected zone beneath the interface. With increasing plunge depth, rotational speed, and dwell time, the T-SF of the PCJs first increased and then decreased, achieving a relatively high value at a plunge depth of 0.4 mm, a rotational speed of 1500 rpm, and a dwell time of 9 s. The fracture types of the PCJs were shear fracture and plug fracture, with the Hook region identified as the weakest zone. Full article

(This article belongs to the Special Issue Metallurgy-Processing-Properties Relationship of Metallic Materials)

► Show Figures

Figure 1

24 pages, 12807 KB

Open AccessArticle

Oriented-Attachment-Driven Heteroepitaxial Growth During Early Coalescence of Single-Crystal Diamond on Iridium: A Combined Multiscale Simulation and Experimental Validation

by Yang Wang, Junhao Chen, Zhe Li, Shilin Yang and Jiaqi Zhu

Crystals 2025, 15(9), 803; https://doi.org/10.3390/cryst15090803 - 12 Sep 2025

Viewed by 710

Abstract

The scalable synthesis of high-quality single-crystal diamond films remains pivotal for next-generation extreme-performance devices. Iridium substrates offer exceptional promise for heteroepitaxy, yet early-stage growth mechanisms limiting crystal quality are poorly understood. An integrated multiscale investigation combining first-principles DFT calculations, molecular dynamics simulations, and [...] Read more.

The scalable synthesis of high-quality single-crystal diamond films remains pivotal for next-generation extreme-performance devices. Iridium substrates offer exceptional promise for heteroepitaxy, yet early-stage growth mechanisms limiting crystal quality are poorly understood. An integrated multiscale investigation combining first-principles DFT calculations, molecular dynamics simulations, and experimental validation is presented to resolve the oriented attachment process governing diamond growth on Ir(100). Robust interfacial bonding at the interface and optimal carbon coverage are revealed to provide thermodynamic driving forces for primary nucleation. A critical angular tolerance enabling defect-free coalescence through crystallographic realignment is identified by molecular dynamics. Concurrent nucleation growth pathways are experimentally confirmed through SEM, AFM, and Raman spectroscopy, where nascent crystallites undergo spontaneous orientational registry to form continuous epitaxial domains. Grain boundary annihilation is observed upon lattice rotation aligning adjacent grains below the critical angle. Crucially, intrinsic atomic steps are generated on the resultant coalesced layer, eliminating conventional etching requirements for homoepitaxial thickening. This work advances fundamental understanding of single-crystal diamond growth mechanisms, facilitating enhanced quality control for semiconductor device manufacturing and quantum applications. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

► Show Figures

Figure 1

18 pages, 3670 KB

Open AccessArticle

Selective Crystallization of Trans-Nerolidol in β-Cyclodextrin: Crystal Structure and Molecular Dynamics Analysis

by Elias Christoforides, Athena Andreou, Polytimi Koskina and Kostas Bethanis

Crystals 2025, 15(9), 802; https://doi.org/10.3390/cryst15090802 - 11 Sep 2025

Viewed by 493

Abstract

Nerolidol (REL), a sesquiterpene with cis and trans isomers, exhibits diverse bioactive and sensory properties. In this study, we integrate single-crystal X-ray diffraction (SC-XRD), molecular docking, molecular dynamics (MD) simulations, and MM/GBSA binding free energy calculations to investigate its inclusion behavior in β-cyclodextrin [...] Read more.

Nerolidol (REL), a sesquiterpene with cis and trans isomers, exhibits diverse bioactive and sensory properties. In this study, we integrate single-crystal X-ray diffraction (SC-XRD), molecular docking, molecular dynamics (MD) simulations, and MM/GBSA binding free energy calculations to investigate its inclusion behavior in β-cyclodextrin (β-CD). Crystallization from a cis/trans mixture yielded a complex containing exclusively the trans isomer, forming a 2:1 host–guest assembly where a head-to-head β-CD dimer encapsulates one trans-REL molecule in an extended conformation. Computational models of cis-REL (bent c1 and extended c8 conformers) also stabilized within the β-CD cavity, with the extended conformer showing the most favorable dynamics. The computed binding affinities for all complexes differed by less than the estimated MM/GBSA uncertainty, indicating no statistically significant preference. Since cis/trans separation of nerolidol and related long-chain terpenoids is of considerable interest, our findings suggest that crystallization selectivity in β-CD inclusion complexes cannot be rationalized solely by binding affinity; instead, it likely arises from crystal packing forces and conformational preferences that govern the solid-state assembly. Full article

(This article belongs to the Section Macromolecular Crystals)

► Show Figures

Figure 1

19 pages, 4277 KB

Open AccessArticle

Comparative Finite Element Analysis of Fatigue Crack Growth in High-Performance Metallic Alloys: Influence of Material Parameters and Paris Law Constants

by Yahya Ali Fageehi and Abdulnaser M. Alshoaibi

Crystals 2025, 15(9), 801; https://doi.org/10.3390/cryst15090801 - 11 Sep 2025

Viewed by 689

Abstract

This study presents a comparative analysis of fatigue crack growth (FCG) in four high-performance crystalline metallic alloys: Inconel 718, Ti-6Al-4V, Aluminum 7075-T6, and ASTM A514 Steel. The Finite Element Method was utilized to simulate crack propagation and quantify the individual and synergistic effects [...] Read more.

This study presents a comparative analysis of fatigue crack growth (FCG) in four high-performance crystalline metallic alloys: Inconel 718, Ti-6Al-4V, Aluminum 7075-T6, and ASTM A514 Steel. The Finite Element Method was utilized to simulate crack propagation and quantify the individual and synergistic effects of key material properties, including Paris Law constants (C and m), yield strength, and modulus of elasticity, on FCG behavior. The analysis integrates simulation-driven parametric studies to quantify the impact on performance indicators (fatigue life cycles, equivalent stress intensity factors, safety factors, von Mises stress, and strain energy), and provides a quantitative analysis of secondary parameters. The results provide a robust, data-driven framework for material selection in aerospace, industrial, and structural applications where fatigue life is a paramount design consideration. Key findings reveal that Inconel 718 exhibits vastly superior fatigue life which is approximately 15 times greater than the next best-performing material, ASTM A514 Steel. Conversely, Ti-6Al-4V demonstrated the lowest fatigue resistance. Full article

(This article belongs to the Special Issue Fatigue and Fracture of Crystalline Metal Structures)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Crystals, Volume 15, Issue 9 (September 2025) – 84 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI