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Crystals
Volume 15
Issue 8
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Crystals, Volume 15, Issue 8 (August 2025) – 79 articles

Cover Story (view full-size image): This work expands the library of copper acetylacetonate adducts to include both volatile and non-volatile ligands. Four pentacoordinate complexes, two coordination polymers and one oligomer were synthesized and are discussed. The use of bidentate ligands yielded one-dimensional coordination polymers, while the use of monodentate ligands produced weaker pentacoordinate adducts. Of particular note is the synthesis and characterization of the pyridine adduct, which, despite its simplicity, has been structurally elucidated for the first time. Furthermore, the new adducts enable correlations to be established between the electronic properties of the ligand substituent and the structural diversity of the complexes. Additionally, Hirshfeld surface analysis was employed to investigate intermolecular interactions in the pyridine derivatives. View this paper
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14 pages, 2657 KB  
Article
The Effect of Heat Treatment on Yellow-Green Beryl Color and Its Enhancement Mechanism
by Binru Hao, Shuxin Zhao and Qingfeng Guo
Crystals 2025, 15(8), 746; https://doi.org/10.3390/cryst15080746 - 21 Aug 2025
Viewed by 616
Abstract
Beryl is classified as a cyclosilicate mineral, and its color is primarily determined by the type and oxidation state of trace elements. In this study, natural yellow-green beryl was used as the research subject, and heat treatment experiments were performed at various temperatures [...] Read more.
Beryl is classified as a cyclosilicate mineral, and its color is primarily determined by the type and oxidation state of trace elements. In this study, natural yellow-green beryl was used as the research subject, and heat treatment experiments were performed at various temperatures under both oxidizing and reducing atmospheres. A combination of analytical techniques, including electron probe microanalysis (EPMA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and ultraviolet-visible spectroscopy (UV-Vis), were employed to systematically investigate the composition, structure, and chromogenic mechanisms of beryl before and after heat treatment. The experimental results indicate that heat treatment under both atmospheres can lead to the transformation of yellow-green beryl into blue, with 500–600 °C under a reducing atmosphere identified as the optimal treatment condition. With increasing temperature, beryl gradually dehydrates, resulting in a faded blue color and reduced transparency. Even after treatment at 700 °C, no significant changes in unit cell parameters were observed, and both type I and type II water were retained, indicating that the color change is not attributed to crystal structure transformation or phase transitions. The study reveals that the essential mechanism of color modification through heat treatment lies in the valence change between Fe2+ and Fe3+ occupying channel and octahedral sites. The observed color variation is attributed to changes in absorption band intensity resulting from charge transfers of O2− → Fe3+ and Fe2+ → Fe3+. This study provides theoretical insights and technical references for the color enhancement of beryl through heat treatment. Full article
(This article belongs to the Collection Topic Collection: Mineralogical Crystallography)
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20 pages, 2262 KB  
Article
Luminescent Arylalkynyltitanocenes: Effect of Modifying the Electron Density at the Arylalkyne Ligand, or Adding Steric Bulk or Constraint to the Cyclopentadienyl Ligand
by Matilda Barker, Samantha C. Walter, Elizabeth A. McCallum, River S. Golden, John H. Zimmerman, Jackson S. McCarthy, Colin D. McMillen and Paul S. Wagenknecht
Crystals 2025, 15(8), 745; https://doi.org/10.3390/cryst15080745 - 21 Aug 2025
Viewed by 579
Abstract
Photocatalysis using complexes of d0 metals with ligand-to-metal charge-transfer (LMCT) excited states is an active area of research. Because titanium is the second most abundant transition metal in the earth’s crust, d0 complexes of TiIV are an appropriate target for [...] Read more.
Photocatalysis using complexes of d0 metals with ligand-to-metal charge-transfer (LMCT) excited states is an active area of research. Because titanium is the second most abundant transition metal in the earth’s crust, d0 complexes of TiIV are an appropriate target for this research. Recently, our group has demonstrated that the arylethynyltitanocene Cp2Ti(C2Ph)2CuBr is not emissive in room-temperature fluid solution, whereas the corresponding Cp* complex, Cp*2Ti(C2Ph)2CuBr, is emissive. The Cp* ligand is hypothesized to provide steric constraint that inhibits excited-state structural rearrangement. However, modifying the structure also changes the orbital character of the excited state. To investigate the impact of the excited-state orbital character on the photophysics, herein we characterize complexes similar to Cp*2Ti(C2Ph)2CuBr—but one with a more electron-rich arylethynyl ligand, ethynyldimethylaniline (C2DMA), and one with a more electron-poor arylethynyl ligand, ethynyl-α,α,α-trifluorotoluene. We have also prepared complexes with the C2DMA ligand but with different Cp ligands that adjust the steric bulk and constraint around the Ti, by replacing the Cp* ligands with either indenyl ligands or an ansa-cyclopentadienyl ligand where the two Cp ligands are bridged by a dimethylsilylene. All four target complexes have been characterized crystallographically and structure activity relationships are highlighted. Full article
(This article belongs to the Special Issue Celebrating the 10th Anniversary of International Crystallography)
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19 pages, 5991 KB  
Article
Temperature- and Emission Wavelength-Dependent Time Responses of Strontium Aluminates
by Virginija Vitola, Tinko Eftimov, Kristian Nikolov, Samia Fouzar and Katrina Krizmane
Crystals 2025, 15(8), 744; https://doi.org/10.3390/cryst15080744 - 20 Aug 2025
Viewed by 529
Abstract
In this paper, we study the temperature- and emission wavelength-dependent time responses of previously reported precursor-driven Eu2+- and Dy3+-doped strontium-aluminate phosphors to create unique luminescent anti-counterfeiting tags suitable for detection with smartphones. A smartphone was used to detect the [...] Read more.
In this paper, we study the temperature- and emission wavelength-dependent time responses of previously reported precursor-driven Eu2+- and Dy3+-doped strontium-aluminate phosphors to create unique luminescent anti-counterfeiting tags suitable for detection with smartphones. A smartphone was used to detect the red–green–blue (RGB) components of the rise and decay time responses of the samples in a temperature range from 0 °C to 100 °C. The RGB color-dependent detection revealed a finer excitation/relaxation kinetics structure of the individual samples, which becomes evident in the decay responses. The results suggest another possibility for multilevel encoding and temperature sensor applications, and provides a foundation for developing a more accurate theoretical model of the energy transitions in phosphorescent materials. Full article
(This article belongs to the Section Polycrystalline Ceramics)
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16 pages, 7539 KB  
Article
Dispersion of Sintered Mg-Ni-Ce Materials for Efficient Hydrogen Storage
by Nuriya Mukhamedova, Arman Miniyazov, Aisara Sabyrtayeva, Timur Tulenbergenov and Ospan Oken
Crystals 2025, 15(8), 743; https://doi.org/10.3390/cryst15080743 - 20 Aug 2025
Viewed by 609
Abstract
This paper presents the results of the effect of dispersion on the structural-phase state of the material for hydrogen storage of the Mg-Ni-Ce system. X-ray phase analysis and scanning electron microscopy studies have shown that the sequential use of mechanical synthesis and spark-plasma [...] Read more.
This paper presents the results of the effect of dispersion on the structural-phase state of the material for hydrogen storage of the Mg-Ni-Ce system. X-ray phase analysis and scanning electron microscopy studies have shown that the sequential use of mechanical synthesis and spark-plasma sintering methods ensures the formation of a stable and dense microstructure with a high content of the intermetallic phase Mg2Ni. As a result of dispersion for 1 h, the sintered material was transferred to a finely dispersed state without changing the phase composition. Increasing the duration of dispersion to 2 h led to the formation of large agglomerates and the destruction of the material structure. For the first time, the dispersion technology was applied to materials of the Mg-Ni-Ce system, pre-sintered by spark-plasma sintering. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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17 pages, 5692 KB  
Article
Investigating the Influence of Cerium Doping on the Structural, Optical, and Electrical Properties of ZnCexCo2−xO4 Zinc Cobaltite Thin Films
by Abdellatif El-Habib, Mohamed Oubakalla, Samir Haloui, Youssef Nejmi, Mohamed El Bouji, Amal Yousfi, Fouad El Mansouri, Abdessamad Aouni, Mustapha Diani and Mohammed Addou
Crystals 2025, 15(8), 742; https://doi.org/10.3390/cryst15080742 - 20 Aug 2025
Viewed by 595
Abstract
Cerium-doped zinc cobaltite spinel thin films, ZnCexCo2−xO4 (0.00≤x≤0.05), were synthesized via spray pyrolysis, and their structural, morphological, optical, and electrical properties were analyzed. X-ray [...] Read more.
Cerium-doped zinc cobaltite spinel thin films, ZnCexCo2−xO4 (0.00≤x≤0.05), were synthesized via spray pyrolysis, and their structural, morphological, optical, and electrical properties were analyzed. X-ray diffraction (XRD) confirmed a cubic spinel structure with a predominant (311) orientation across all compositions. Raman spectroscopy further verified this phase, revealing four active vibrational modes at 180 cm−1, 470 cm−1, 515 cm−1, and 682 cm−1. Scanning electron microscopy (SEM) indicated a uniform grain distribution, while energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of Ce, Zn, Co, and O. Optical measurements revealed two distinct bandgaps, decreasing from 2.32 eV to 2.20 eV for the lower-energy transition and from 3.38 eV to 3.18 eV for the higher-energy transition. Hall effect measurements confirmed p-type conductivity in all films. Electrical analysis showed a reduction in resistivity, from 280.3 Ω·cm to 15.4 Ω·cm, along with an increase in carrier concentration from 1.15 × 1016 cm−3 to 8.15 × 1017 cm−3 with higher Ce content. These results demonstrate that spray pyrolysis is a cost-effective and scalable method for producing Ce-doped ZnCo2O4 thin films with tunable properties, making them suitable for electronic and optoelectronic applications. Full article
(This article belongs to the Special Issue Advances in Thin-Film Materials and Their Applications)
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10 pages, 1740 KB  
Article
A Novel System for Crystal Polymorph Discovery via Selective-Wavelength Infrared Irradiation Using Metamaterials
by Yoshio Kondo, Tsuyoshi Totani, Satoru Odashima, Daiki Kato and Norimitsu Tohnai
Crystals 2025, 15(8), 741; https://doi.org/10.3390/cryst15080741 - 20 Aug 2025
Viewed by 616
Abstract
The control of crystal polymorphs is central to the design of pharmaceuticals and functional materials. Conventionally, crystal polymorph production has been controlled primarily by adjusting chemical and thermodynamic parameters. In this study, we developed a device capable of emitting infrared radiation at selected [...] Read more.
The control of crystal polymorphs is central to the design of pharmaceuticals and functional materials. Conventionally, crystal polymorph production has been controlled primarily by adjusting chemical and thermodynamic parameters. In this study, we developed a device capable of emitting infrared radiation at selected wavelengths using a novel material having a “MIM structure” which is a type of metamaterial. With this device, we propose a new approach to crystal polymorph control through the irradiation of narrow-band infrared radiation that coincides with the infrared absorption band of specific functional groups. In this paper, we present the design and operating principle of a new crystallization system, and as an application example, we report the experimental results of controlling the crystal polymorphs of Ritonavir, an active pharmaceutical ingredient. Full article
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11 pages, 2254 KB  
Article
Behaviors of Gas-Rich Crystalline Fluid Inclusions
by Luis Salgado, François Faure and Gérard Coquerel
Crystals 2025, 15(8), 740; https://doi.org/10.3390/cryst15080740 - 20 Aug 2025
Viewed by 483
Abstract
A novel behavior of fluid inclusions (FIs) in crystals is reported in this study. Typically, at “high” temperature, FIs in molecular crystals become faceted, adopting the morphology of a single crystal. Usually, upon cooling, these faceted FIs develop into rounded cavities containing the [...] Read more.
A novel behavior of fluid inclusions (FIs) in crystals is reported in this study. Typically, at “high” temperature, FIs in molecular crystals become faceted, adopting the morphology of a single crystal. Usually, upon cooling, these faceted FIs develop into rounded cavities containing the mother solution with a retreat gas bubble. After annealing at low temperature, the FIs reshape back into a negative-crystal morphology, but the gas bubble remains. This latter process can take from minutes to very long times depending on the storage temperature and solubility. Investigations into the behavior of FIs of dicumyl peroxide (DCP) under fast cooling rates have revealed a morphological transition from negative crystals to FIs with a holly-leaf shape. The spikes of the holly-leaf-shaped FIs point toward the corners of the former negative crystal, and the sizes of the gas bubbles exceed those of conventional retreat bubbles. Therefore, it is likely that this phenomenon is linked to rapid cooling and an excess of CO2 dissolved in the mother solution from which the DCP single crystals were grown. The concentration of the solution inside the FIs rapidly increases after the nucleation of this large gas bubble. This is consistent with a sharp acceleration of inward crystal growth immediately after its appearance. Interestingly, FIs in pyroclastic olivine crystals grown from CO2-rich lava can also present a holly-leaf shape. Thus, this non-equilibrium morphological transition may be relatively common. Full article
(This article belongs to the Section Industrial Crystallization)
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13 pages, 2635 KB  
Article
Structure and Nonlinear Optical Characterization of a New Acentric Crystal of a 4-Hydroxybenzohydrazide Derivative
by Emanuela Santagata, Yovan de Coene, Stijn Van Cleuvenbergen, Koen Clays, Emmanuele Parisi, Fabio Borbone and Roberto Centore
Crystals 2025, 15(8), 739; https://doi.org/10.3390/cryst15080739 - 20 Aug 2025
Viewed by 532
Abstract
We report the crystal structure and nonlinear optical (NLO) characterization of the monohydrate form of N′-[(E)-(2-fluorophenyl)methylidene]-4-hydroxybenzohydrazide (o-FHH), an organic compound showing strong potential for second-order nonlinear optical applications. The compound crystallizes in a non-centrosymmetric tetragonal space group. The supramolecular features of [...] Read more.
We report the crystal structure and nonlinear optical (NLO) characterization of the monohydrate form of N′-[(E)-(2-fluorophenyl)methylidene]-4-hydroxybenzohydrazide (o-FHH), an organic compound showing strong potential for second-order nonlinear optical applications. The compound crystallizes in a non-centrosymmetric tetragonal space group. The supramolecular features of the novel crystal structure are strongly related to the role of the water molecule that stabilized columns of o-FHH through strong hydrogen bonding interactions. This structural feature is reflected in the high thermal stability of the compound, which is evidenced by its ability to withstand temperatures in excess of 100 °C without losing the water molecule. Second-harmonic generation (SHG) imaging confirms bulk nonlinearity throughout the entire volume of the crystal, consistent with the acentric class of the novel compound. The combination of a dense hydrogen-bonding network, structural robustness, and the ability to grow millimeter-sized single crystals makes o-FHH a good candidate for further development as an organic NLO material. Full article
(This article belongs to the Section Organic Crystalline Materials)
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17 pages, 10574 KB  
Article
Evaluation of Corrosion Behavior of Zn–Al–Mg-Coated Steel in Corrosive Heterogeneous Soil
by Pedro Javier Lloreda-Jurado and Ernesto Chicardi
Crystals 2025, 15(8), 738; https://doi.org/10.3390/cryst15080738 - 20 Aug 2025
Viewed by 893
Abstract
The long-term durability of steel structures in contact with soil remains a critical challenge due to the complex and aggressive nature of many soil environments. This study presents a thorough evaluation of the corrosion resistance and microstructural evolution of Magnelis® ZM430-coated steel [...] Read more.
The long-term durability of steel structures in contact with soil remains a critical challenge due to the complex and aggressive nature of many soil environments. This study presents a thorough evaluation of the corrosion resistance and microstructural evolution of Magnelis® ZM430-coated steel exposed to highly aggressive, heterogeneous soils. Gravimetric analysis revealed that the Magnelis® ZM430 coating exhibits low corrosion rates and enhanced initial barrier properties, even under severe soil conditions. Although the literature frequently reports that Zn–Al–Mg coatings outperform conventional hot-dip galvanized coatings, our results highlight that this superiority is not universal and may be limited under highly aggressive, heterogeneous soils. Microstructural characterization by optical microscopy, SEM/EDS, and XRD demonstrated that the as-received coating consists of a homogeneous layer with well-distributed Zn-, MgZn2-, and Al-rich phases. Upon soil exposure, corrosion preferentially initiates in the Mg- and Al-rich interdendritic and eutectic regions, leading to selective phase depletion and localized breakdown of the protective layer. Despite these localized vulnerabilities, the overall performance of Magnelis® ZM430 remains superior, especially during the early stages of exposure. While no direct comparisons were performed in this work, our findings align with previous literature reporting superior performance of Zn–Al–Mg coatings compared to conventional hot-dip galvanized coatings in similar environments. Importantly, the integration of precise corrosion rate data with detailed soil characterization enables accurate prediction of coating service life, allowing for optimized coating thickness selection and proactive maintenance planning. These findings underscore the value of combining advanced Zn–Al–Mg coatings with site-specific environmental assessment to ensure the long-term integrity of buried steel infrastructure. Full article
(This article belongs to the Special Issue Advanced Alloys for Aggressive Environments: Challenges and Breakthroughs)
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18 pages, 1562 KB  
Article
Continuous Symmetry Breaking and Complexity of Biological Membranes
by Samo Kralj, Veronika Kralj-Iglič and Aleš Iglič
Crystals 2025, 15(8), 737; https://doi.org/10.3390/cryst15080737 - 20 Aug 2025
Viewed by 630
Abstract
We consider domain-type patterns in biological membranes that possess an in-plane membrane order. Domains are inseparably linked to topological defects, and many features related to them can be guessed based on universal topological arguments. However, much more complex membrane patterns are typically observed. [...] Read more.
We consider domain-type patterns in biological membranes that possess an in-plane membrane order. Domains are inseparably linked to topological defects, and many features related to them can be guessed based on universal topological arguments. However, much more complex membrane patterns are typically observed. As possible generators of such configurations, we analyze two relatively simple and universal phenomena. Both are based on continuous symmetry breaking (CSB), which manifests ubiquitously in all branches of physics. We present the Imry–Ma argument which, in addition to CSB, requests the presence of uncorrelated random-field-type disorder. Next, we discuss the Kibble–Zurek mechanism. In addition to CSB it considers dynamical slowing when a relevant phase transition is approached. These approaches were originally introduced in magnetism and cosmology, respectively. We adapt them to effectively two-dimensional membranes and discuss their potential role in membrane structure formation. Full article
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38 pages, 6660 KB  
Review
Field-Effect Crystal Engineering in Proton–π-Electron Correlated Systems
by Sachio Horiuchi, Hiromi Minemawari, Jun’ya Tsutsumi and Shoji Ishibashi
Crystals 2025, 15(8), 736; https://doi.org/10.3390/cryst15080736 - 19 Aug 2025
Viewed by 740
Abstract
Dielectric crystals with switchable electric polarizations represent the key functional materials utilized for a broad range of practical applications. They allow for academically intriguing platforms, where the use of a strong external electric field can potentially unveil hidden crystal phases. Proton–π-electron correlated bistable [...] Read more.
Dielectric crystals with switchable electric polarizations represent the key functional materials utilized for a broad range of practical applications. They allow for academically intriguing platforms, where the use of a strong external electric field can potentially unveil hidden crystal phases. Proton–π-electron correlated bistable systems turn out to be promising for exploring such electrically induced crystal polymorphisms, mainly because strong π-electronic polarization can be sensitively switched depending on mobile hydrogen locations. Pseudo-symmetry and hydrogen disorder are utilized as clues for the data mining of the Cambridge Structural Database in the search for molecular candidates with novel switchable dielectrics. The polarization hysteresis, electrostriction, and second harmonic generation of the candidates were experimentally evaluated, together with the re-inspection of crystal structure. This feature article highlights the rich variation and competition of some candidate polarization configurations and switching modes in close relation to high and efficient electrical energy storage/discharge, large electrostriction effects, polarization rotations, and multistage switching phenomena. The experimental findings are well-reproduced by the computational optimization of crystal structure and the simulation of the switchable polarization, piezoelectric coefficients, and relative stability for each of the real or hypothetical hydrogen-ordered crystal phases. Effective prediction and strategic design are thereby guaranteed by systematically understanding the appropriate integration of experimental, computational, and data sciences. Full article
(This article belongs to the Special Issue Polymorphism and Phase Transitions in Crystal Materials)
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16 pages, 33192 KB  
Article
Microstructure and Mechanical Property Tailoring in Asymmetrically Shear-Extruded Mg-2.0Al-0.8Sn-0.5Ca Alloys via Zn Addition
by Chao Wang, Wen-Qi Li, Hai Deng, Huai-Qiang Zhang, Jin-Long Cai and Zhi-Gang Li
Crystals 2025, 15(8), 735; https://doi.org/10.3390/cryst15080735 - 19 Aug 2025
Viewed by 522
Abstract
This study systematically examines the influence of Zn addition (≤0.6 wt.%) on the microstructure and mechanical properties of Mg-2Al-0.8Sn-0.5Ca (wt.%) alloys. Minor Zn alloying marginally increases secondary phase fraction in as-cast alloys, with complete Zn dissolution achieved after solution treatment and asymmetric severe [...] Read more.
This study systematically examines the influence of Zn addition (≤0.6 wt.%) on the microstructure and mechanical properties of Mg-2Al-0.8Sn-0.5Ca (wt.%) alloys. Minor Zn alloying marginally increases secondary phase fraction in as-cast alloys, with complete Zn dissolution achieved after solution treatment and asymmetric severe shear extrusion. Extruded alloys exhibit non-monotonic strength evolution with Zn content, peaking at 0.2 wt.% Zn (yield strength ≈ 235.1 MPa, ultimate tensile strength ≈ 289.2 MPa), while elongation reaches 16.1%. This strength enhancement originates from synergistic grain boundary, solid-solution, and dislocation strengthening mechanisms. These results demonstrate Zn’s critical role in optimizing the strength-ductility balance of rare-earth-free magnesium alloys. Full article
(This article belongs to the Section Crystalline Metals and Alloys)
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21 pages, 37808 KB  
Article
Coarse-Graining and Classifying Massive High-Throughput XFEL Datasets of Crystallization in Supercooled Water
by Ervin S. H. Chia, Tim B. Berberich, Egor Sobolev, Jayanath C. P. Koliyadu, Patrick Adams, Tomas André, Fabio Dall Antonia, Sebastian Cardoch, Emiliano De Santis, Andrew Formosa, Björn Hammarström, Michael P. Hassett, Seonmyeong Kim, Marco Kloos, Romain Letrun, Janusz Malka, Diogo Melo, Stefan Paporakis, Tokushi Sato, Philipp Schmidt, Oleksii Turkot, Mohammad Vakili, Joana Valerio, Tej Varma Yenupuri, Tong You, Raphaël de Wijn, Gun-Sik Park, Brian Abbey, Connie Darmanin, Saša Bajt, Henry N. Chapman, Johan Bielecki, Filipe R. N. C. Maia, Nicusor Timneanu, Carl Caleman, Andrew V. Martin, Ruslan P. Kurta, Jonas A. Sellberg and Ne-te Duane Lohadd Show full author list remove Hide full author list
Crystals 2025, 15(8), 734; https://doi.org/10.3390/cryst15080734 - 19 Aug 2025
Viewed by 689
Abstract
Ice crystallization in supercooled water is a complex phenomenon with far-reaching implications across scientific disciplines, including cloud formation physics and cryopreservation. Experimentally studying such complexity can be a highly data-driven and data-hungry endeavor because of the need to record rare events that cannot [...] Read more.
Ice crystallization in supercooled water is a complex phenomenon with far-reaching implications across scientific disciplines, including cloud formation physics and cryopreservation. Experimentally studying such complexity can be a highly data-driven and data-hungry endeavor because of the need to record rare events that cannot be triggered on demand. Here, we describe such an experiment comprising 561 million images of X-ray free-electron laser (XFEL) diffraction patterns (2.3 PB raw data) spanning the disorder-to-order transition in micrometer-sized supercooled water droplets. To effectively analyze these patterns, we propose a data reduction (i.e., coarse-graining) and dimensionality reduction (i.e., principal component analysis) strategy. We show that a simple set of criteria on this reduced dataset can efficiently classify these patterns in the absence of reference diffraction signatures, which we validated using more precise but computationally expensive unsupervised machine learning techniques. For hit-finding, our strategy attained 98% agreement with our cross-validation. We speculate that these strategies may be generalized to other types of large high-dimensional datasets generated at high-throughput XFEL facilities. Full article
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13 pages, 3304 KB  
Article
ANN-Based Prediction of OSL Decay Curves in Quartz from Turkish Mediterranean Beach Sand
by Mehmet Yüksel, Fırat Deniz and Emre Ünsal
Crystals 2025, 15(8), 733; https://doi.org/10.3390/cryst15080733 - 19 Aug 2025
Viewed by 1100
Abstract
Quartz is a widely used mineral in dosimetric and geochronological applications due to its stable luminescence properties under ionizing radiation. This study presents an artificial neural network (ANN)-based approach to predict the optically stimulated luminescence (OSL) decay curves of quartz extracted from Mediterranean [...] Read more.
Quartz is a widely used mineral in dosimetric and geochronological applications due to its stable luminescence properties under ionizing radiation. This study presents an artificial neural network (ANN)-based approach to predict the optically stimulated luminescence (OSL) decay curves of quartz extracted from Mediterranean beach sand samples in Turkey. Experimental OSL signals were obtained from quartz samples irradiated with beta doses ranging from 0.1 Gy to 1034.9 Gy. The dataset was used to train ANN models with three different learning algorithms: Levenberg–Marquardt (LM), Bayesian Regularization (BR), and Scaled Conjugate Gradient (SCG). Forty-seven decay curves were used for training and three for testing. The ANN models were evaluated based on regression accuracy, training–validation–test performance, and their predictive capability for low, medium, and high doses (1 Gy, 72.4 Gy, 465.7 Gy). The results showed that BR achieved the highest overall regression (R = 0.99994) followed by LM (R = 0.99964) and SCG (R = 0.99820), confirming the superior generalization and fits across all dose ranges. LM performs optimally at low-to-moderate doses, and SCG delivers balanced yet slightly noisier predictions. The proposed ANN-based method offers a robust and effective alternative to conventional kinetic modeling approaches for analyzing OSL decay behavior and holds considerable potential for advancing luminescence-based retrospective dosimetry and OSL dating applications. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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12 pages, 2329 KB  
Article
Comparative Analysis of the Substituent Effects on the Supramolecular Structure of N′-(4-Methyl-2-nitrophenyl)benzohydrazide and N′-(2-Nitro-(4-trifluoromethyl)phenyl)benzohydrazide)
by Christos P. Constantinides, Syed Raza, Fadwat Bazzi, Nisreen Sharara and Simona Marincean
Crystals 2025, 15(8), 732; https://doi.org/10.3390/cryst15080732 - 19 Aug 2025
Viewed by 768
Abstract
N′-Phenylbenzohydrazides are valuable precursors for air- and moisture-stable Blatter radicals, with applications in magnetism and spintronics. This study presents the single-crystal X-ray structures of N′-(4-methyl-2-nitrophenyl)benzohydrazide (I) and N′-(2-nitro-(4-trifluoromethyl)phenyl)benzohydrazide (II), highlighting the influence of substituents on supramolecular [...] Read more.
N′-Phenylbenzohydrazides are valuable precursors for air- and moisture-stable Blatter radicals, with applications in magnetism and spintronics. This study presents the single-crystal X-ray structures of N′-(4-methyl-2-nitrophenyl)benzohydrazide (I) and N′-(2-nitro-(4-trifluoromethyl)phenyl)benzohydrazide (II), highlighting the influence of substituents on supramolecular arrangement. Compounds I and II are found to crystallize within the monoclinic crystal system, with the space groups I2/a and P21/n, respectively, with centrosymmetric, one-dimensional columnar packing driven by π-π stacking. In I, π-π dimers form between benzoyl rings (3.018 Å), with additional stacking between aryls (3.408 Å) of neighboring dimers. In II, alternating benzoyl and aryl rings stack with interplanar distances of 2.681 and 2.713 Å. Bifurcated intra- and intermolecular hydrogen bonds (1.938–2.478 Å) further stabilize the packing. Compound II exhibits inter-stack F···F contacts (2.924 Å), attributed to steric effects. The trifluoromethyl group enhances N′NCO-NO2 conjugation, resulting in a near-parallel arrangement of aromatic rings and planar geometry at the N′ nitrogen. In contrast, compound I shows reduced conjugation, leading to pyramidalization at the N′ nitrogen and increased hydrazide bond flexibility, as seen in the 56° angle between aromatic rings. Full article
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15 pages, 2317 KB  
Article
Evolution of Mechanical Properties, Mineral Crystallization, and Micro-Gel Formation in Alkali-Activated Carbide Slag Cementitious Materials
by Yonghao Huang, Guodong Huang, Zhenghu Han, Fengan Zhang, Meng Liu and Jinyu Hao
Crystals 2025, 15(8), 731; https://doi.org/10.3390/cryst15080731 - 19 Aug 2025
Viewed by 551
Abstract
For efficient utilization of carbide slag (CS) waste to high-value building materials, in this study, CS and ground granulated blast furnace slag (GBFS) were used as primary raw materials to prepare alkali-activated cementitious systems under strong alkaline excitation. Multiscale mechanisms involving macroscopic mechanical [...] Read more.
For efficient utilization of carbide slag (CS) waste to high-value building materials, in this study, CS and ground granulated blast furnace slag (GBFS) were used as primary raw materials to prepare alkali-activated cementitious systems under strong alkaline excitation. Multiscale mechanisms involving macroscopic mechanical property development were investigated. Microstructural characterization elucidated how raw material composition affected mineral crystal formation and transformation while revealing enhancement mechanisms governing micro-gel network structure formation and evolution dynamics. The results indicate that excessive calcium components coupled with deficient Si–Al sources in CS severely inhibit the formation of C-S-H and C-A-S-H gel phases, consequently impeding mechanical performance development. Also, GBFS incorporation offsets inherent silicon–aluminum deficiencies. Active [SiO4]4− and [AlO4]5− released from GBFS drive polycondensation reactions toward advanced polymerization states. Compressive strength has a nonlinear growth kinetics characterized by rapid initial ascent, followed by asymptotic plateauing as GBFS content increases. Optimal comprehensive performance emerges at a 5:5 GBFS-to-CS mass ratio, where 28d compressive strength reaches 47.5 MPa. Full article
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14 pages, 9710 KB  
Article
Annealing-Driven Recrystallization of Mechanically Deformed Ce-Doped ZrO2 Ceramics
by Natalia O. Volodina and Rafael I. Shakirzyanov
Crystals 2025, 15(8), 730; https://doi.org/10.3390/cryst15080730 - 17 Aug 2025
Viewed by 464
Abstract
During the annealing, recrystallization processes in ceramics can occur, manifested in the formation of new grains, grain-boundary migration, and grain coarsening. It was expected that recrystallization in mechanically deformed zones, which contain residual stresses and high defect densities, will proceed in a different [...] Read more.
During the annealing, recrystallization processes in ceramics can occur, manifested in the formation of new grains, grain-boundary migration, and grain coarsening. It was expected that recrystallization in mechanically deformed zones, which contain residual stresses and high defect densities, will proceed in a different way compared to the surrounding, relaxed material. Characterizing these spatial variations in defect evolution, phase transformations, and microstructural recovery is essential for predicting performance and avoiding critical structural changes when designing zirconia-based ceramics for high-temperature, load-bearing applications. To study these effects, we used partially stabilized Ce-doped ZrO2 ceramics, fabricated by solid-state synthesis. Phase composition, structural features, and morphology of these ceramics were studied using Raman spectroscopy, XRD and SEM before and after annealing in the mechanically stressed and relaxed regions. In mechanically deformed regions a more pronounced phase transformation from monoclinic to tetragonal was observed compared to relaxed zones. This result indicates that strain can facilitate tetragonal phase formation in zirconia ceramics when the material is subjected to elevated temperatures. Mechanical stresses should be taken into account when fabricating ceramic components, as they can induce phase transformation during heat treatments and change the properties of ceramics significantly. Full article
(This article belongs to the Special Issue Microstructure Evolution During Cold and Hot Deformation)
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14 pages, 3458 KB  
Article
Synthesis and Characterization of [Co(tta)2(4,4′-bipy)2.CHCl3]n: A Coordination Polymer with Sulfur–Sulfur Interactions
by Mohammed A. Al-Anber, Deeb Taher, Petra Ecorchard, Matous Kloda, Yasser Mahmoud Aboelmagd and Heinrich Lang
Crystals 2025, 15(8), 729; https://doi.org/10.3390/cryst15080729 - 16 Aug 2025
Viewed by 678
Abstract
Coordination polymer [{Co(tta)2(4,4′-bipy)}n] (1) (tta = 4,4,4 trifluoro-1-(2-thienyl)-1,3-butanedionate; 4,4′-bipy = 4,4′-bipyridine) was synthesized by reacting [Co(tta)2-(H2O)2] with equivalent of 4,4′-bipy, whereby the aqua ligands in [Co(tta)2-(H2O)2 [...] Read more.
Coordination polymer [{Co(tta)2(4,4′-bipy)}n] (1) (tta = 4,4,4 trifluoro-1-(2-thienyl)-1,3-butanedionate; 4,4′-bipy = 4,4′-bipyridine) was synthesized by reacting [Co(tta)2-(H2O)2] with equivalent of 4,4′-bipy, whereby the aqua ligands in [Co(tta)2-(H2O)2] were replaced by 4,4′-bipy ligand. Thermal behavior, investigated via thermogravimetric analysis (TGA), revealed that 1 decomposes between 290 and 400 °C. The solid-state structure of 1 was confirmed by single-crystal X-ray diffraction, which established its polymeric nature of 1. Each monomer unit of 1 features a cobalt center in an octahedral coordination environment, with two equatorially chelating tta ligands and one axially oriented 4,4′-bipy ligand. Sulfur–sulfur interactions lead to the formation of a two-dimensional supramolecular network. In addition, compound 1 is stabilized by various intermolecular interactions, including C-H···π, C-F···F-C, and C-H···F-C contacts. Hirshfeld surface analysis and 2D-fingerprint plots were employed to further investigate the non-covalent intermolecular interactions in the solid state, providing strong evidence for their role in stabilizing the crystal structure. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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16 pages, 3710 KB  
Article
Janus Ga2SSe-Based van der Waals Heterojunctions as a Class of Promising Candidates for Photocatalytic Water Splitting: A DFT Investigation
by Fan Yang, Marie-Christine Record and Pascal Boulet
Crystals 2025, 15(8), 728; https://doi.org/10.3390/cryst15080728 - 16 Aug 2025
Viewed by 613
Abstract
Addressing global energy and environmental issues calls for the development of effective photocatalysts capable of enabling solar-driven water splitting, a key route toward sustainable hydrogen generation. In this work, we conducted a detailed density functional theory (DFT) study on three bilayer van der [...] Read more.
Addressing global energy and environmental issues calls for the development of effective photocatalysts capable of enabling solar-driven water splitting, a key route toward sustainable hydrogen generation. In this work, we conducted a detailed density functional theory (DFT) study on three bilayer van der Waals (vdW) heterojunctions, Ga2SSe/GaP, Ga2SSe/PtSSe, and Ga2SSe/SnSSe, each explored in four distinct stacking configurations, with Ga2SSe serving as the base monolayer. We assessed their structural stability, electronic properties, and optical responses to determine their suitability for photocatalytic water splitting. The analysis showed that Ga2SSe/GaP and Ga2SSe/SnSSe exhibit type-II band alignment, while Ga2SSe/PtSSe displays a type-I alignment. Electrostatic potential profiles and Bader charge calculations identified SeGa2S/SSnSe and SeGa2S/SeSnS as direct Z-scheme systems, offering efficient charge carrier separation and robust redox potential. For effective water splitting, the band edges must straddle the water redox potentials. Our results indicate that configurations A and B in Ga2SSe/GaP, along with C and D in Ga2SSe/SnSSe, fulfill this requirement. These four configurations also exhibit strong absorption in both the visible and ultraviolet spectral ranges. Notably, configurations C and D of Ga2SSe/SnSSe achieve high solar-to-hydrogen (STH) efficiencies, reaching 38.44% and 21.75%, respectively. Overall, our findings suggest that these direct Z-scheme heterostructures are promising candidates for water splitting photocatalysis. Full article
(This article belongs to the Section Materials for Energy Applications)
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14 pages, 2419 KB  
Article
Combined Lithium-Rich Czochralski Growth and Diffusion Method for Z-Cut Near-Stoichiometric Lithium Niobate Crystals and the Study of Periodic Domain Structures
by Xuefeng Xiao, Yan Zhang, Han Zhang, Jiayi Chen, Yan Huang, Jiashun Si, Shuaijie Liang, Qingyan Xu, Huan Zhang, Lingling Ma, Cui Yang and Xuefeng Zhang
Crystals 2025, 15(8), 727; https://doi.org/10.3390/cryst15080727 - 16 Aug 2025
Viewed by 540
Abstract
This paper presents the preparation of Z-cut near-stoichiometric lithium niobate (NSLN) wafers using a combined process of the lithium-rich Czochralski growth and diffusion methods. The fabricated Z-cut NSLN wafers exhibited outstanding comprehensive performance, including a high Curie temperature of up to 1200 °C, [...] Read more.
This paper presents the preparation of Z-cut near-stoichiometric lithium niobate (NSLN) wafers using a combined process of the lithium-rich Czochralski growth and diffusion methods. The fabricated Z-cut NSLN wafers exhibited outstanding comprehensive performance, including a high Curie temperature of up to 1200 °C, a refractive index gradient in the diameter direction below 1.5 × 10−4 cm−1, and a UV absorption edge shifted 14 nm toward the ultraviolet region compared to congruent lithium niobate crystals, with a coercive field of 1268 V/mm. Additionally, the wafers demonstrated excellent processing characteristics, with the bow of 4-inch wafers controlled within 55 μm, surpassing the machining standards of traditional lithium niobate wafers of the same size. These results indicated the highly uniform chemical stoichiometry and crystallization quality of the wafers. Leveraging the high uniformity and low coercive field of the wafers, periodic triangular domain structure arrays were successfully fabricated, laying the foundation for domain engineering design in electro-optic deflectors and switching devices. This study not only achieves the scalable preparation of NSLN wafers but also provides a reliable technical solution for their practical applications in high-performance electro-optic devices. Full article
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19 pages, 2925 KB  
Article
Study on Modifying Mechanical Properties and Electronic Structure of Aerospace Material γ-TiAl Alloy
by Mingji Fang, Chunhong Zhang and Wanjun Yan
Crystals 2025, 15(8), 726; https://doi.org/10.3390/cryst15080726 - 16 Aug 2025
Viewed by 572
Abstract
γ-TiAl alloy is a lightweight high-temperature structural material, featuring low density, excellent high-temperature strength, creep resistance, etc. It is a key material in the aerospace field. However, the essential defects of γ-TiAl alloys, such as poor room-temperature plasticity and low fracture toughness, have [...] Read more.
γ-TiAl alloy is a lightweight high-temperature structural material, featuring low density, excellent high-temperature strength, creep resistance, etc. It is a key material in the aerospace field. However, the essential defects of γ-TiAl alloys, such as poor room-temperature plasticity and low fracture toughness, have become the biggest obstacles to their practical application. Therefore, in this paper, the physical mechanism of modification of the mechanical properties and electronic structure of γ-TiAl alloys by doping with Sc, V, and Si was investigated by using the first-principles pseudopotential plane wave method. This paper specifically calculates the geometric structure, phonon spectrum, mechanical properties, electron density of states, Mulliken population analysis, and differential charge density of γ-TiAl alloys before and after doping. The results show that after doping, the structural parameters of γ-TiAl have changed significantly, and the doping models all have thermodynamic stability. The B, G, and E values of the doped system are, respectively, within the range of 94–112, 57–69, and 143–170 GPa, indicating that the material’s ability to resist compressive deformation is weakened. Moreover, the B/G values change from 1.5287 to 1.6350, 1.7279, and 1.6327, respectively, and a transformation from brittleness to plasticity occurs. However, it is still lower than the critical value of 1.75, indicating that the doped γ-TiAl alloy material retains its high-strength characteristics while also exhibiting a certain degree of toughness. The total elastic anisotropy index of the doped system increases, and the degree of anisotropy of mechanical behavior significantly increases. The total electron density of states diagram indicates that γ-TiAl alloys possess conductive properties. The covalent interactions between doped atoms and adjacent atoms have been weakened to varying degrees, which is manifested as a significant change in the charge distribution around each atom. The above results indicate that the doping of Sc, V, and Si can effectively tune the mechanical properties and electronic structure of γ-TiAl alloys. Full article
(This article belongs to the Special Issue Microstructure and Properties of Metals and Alloys)
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17 pages, 3778 KB  
Article
Optimization of Printing Parameters Based on Computational Fluid Dynamics (CFD) for Uniform Filament Mass Distribution at Corners in 3D Cementitious Material Printing
by Zhixin Liu, Liang Si, Yebao Liu, Mingyang Li and Teck Neng Wong
Crystals 2025, 15(8), 725; https://doi.org/10.3390/cryst15080725 - 15 Aug 2025
Viewed by 441
Abstract
Three-dimensional cementitious material printing (3DCMP) enables structures with complex geometry to be fabricated. Printed filament quality is significantly affected by the mass distribution at its corners. Although fruitful results have been obtained, a significant gap exists in systematically investigating the impact of comprehensive [...] Read more.
Three-dimensional cementitious material printing (3DCMP) enables structures with complex geometry to be fabricated. Printed filament quality is significantly affected by the mass distribution at its corners. Although fruitful results have been obtained, a significant gap exists in systematically investigating the impact of comprehensive parameters on this mass distribution. Therefore, the cross-section ratio Φ (Φ = So/Su) of the filament is proposed as a measurement to evaluate the mass distribution at corners. Then, the impacts of printing process parameters, including the tool path radius R, nozzle aspect ratio φ, and relative nozzle travel speed ζ, on the filament mass distribution are investigated using computational fluid dynamics (CFD). The flow mechanism is elaborated using CFD for cementitious material printing at corners. It was found that the material flow mechanism caused by the combined effects of the printing process parameters affects the filament mass distribution significantly. Some material spills out from the overfilled zone to the underfilled zone during the deposition process. Additionally, printing process windows were identified to ensure acceptable printing quality using a support vector machine (SVM). A new printing window is identified using transfer learning, which can save data resources compared to the SVM method. Finally, the experimental results show the feasibility and effectiveness of the proposed methods in printing process window determination. Full article
(This article belongs to the Special Issue Machine Learning for Material and Process Optimization in Additive Manufacturing)
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16 pages, 4680 KB  
Article
Combined Approach to the Synthesis of WC-(Fe, Ni) Hard Alloys: Mechanical Activation and Spark Plasma Sintering
by Gulzhaz Uazyrkhanova, Yernat Kozhakhmetov, Madina Aidarova, Małgorzata Rutkowska-Gorczyca and Yerkezhan Tabiyeva
Crystals 2025, 15(8), 724; https://doi.org/10.3390/cryst15080724 - 14 Aug 2025
Viewed by 545
Abstract
This paper presents a combined approach to the synthesis of WC-(Fe, Ni) hard alloys obtained by mechanical activation and spark plasma sintering (SPS). The main attention at this stage of the work is paid to studying the evolution of the morphology and phase [...] Read more.
This paper presents a combined approach to the synthesis of WC-(Fe, Ni) hard alloys obtained by mechanical activation and spark plasma sintering (SPS). The main attention at this stage of the work is paid to studying the evolution of the morphology and phase composition of WC-(Fe, Ni) powder mixtures during high-energy milling and their subsequent sintering by the SPS method. The study analyzed the effect of the mechanosynthesis time and the binder phase content on the change in the average particle size, the degree of defect formation, and the phase composition of the powders. It was found that an increase in the milling time to 240 min promotes the formation of the WC nanocrystalline structure and the accumulation of microdefects, which is accompanied by a decrease in the average particle size and an increase in the dislocation density. The X-ray phase analysis of the samples after SPS confirmed the preservation of the WC phase and the formation of the γ-(Fe, Ni) matrix without the formation of secondary carbide phases. The analysis of sample shrinkage showed three main stages: initial compaction, intense shrinkage, and structure stabilization. The obtained data demonstrate that optimization of the parameters of mechanical activation and SPS allow for effective control of the phase composition and morphology of WC-(Fe, Ni) powders, which opens up opportunities for their subsequent study in conditions of aggressive environments and radiation exposure. Full article
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21 pages, 2821 KB  
Article
Effect of Cr, Mo, and W Contents on the Semiconductive Properties of Passive Film of Ferritic Stainless Steels
by Seung-Heon Choi, Young-Ran Yoo, Young-Cheon Kim and Young-Sik Kim
Crystals 2025, 15(8), 723; https://doi.org/10.3390/cryst15080723 - 14 Aug 2025
Viewed by 597
Abstract
This study investigated the influence of Cr, Mo, and W alloying elements incorporated into ferritic stainless steel on the characteristics of passive films formed under acidic chloride conditions. Electrochemical assessments demonstrated that increasing the amounts of Cr, Mo, and W reduces passive current [...] Read more.
This study investigated the influence of Cr, Mo, and W alloying elements incorporated into ferritic stainless steel on the characteristics of passive films formed under acidic chloride conditions. Electrochemical assessments demonstrated that increasing the amounts of Cr, Mo, and W reduces passive current density and enhances polarization resistance. Through XPS analysis, it was determined that the passive film exhibits a double-layer structure, consisting of an inner layer rich in metal oxides and an outer layer containing metal oxy-anions. Mott–Schottky analysis indicated the presence of both p-type and n-type semiconducting properties. To clarify the effect of these alloying elements on the passive films at the surface of stainless steel, this work introduces a new parameter termed the “Bipolar Index,” defined as |p-type slope| + |n-type slope|. With higher Cr, Mo, and W contents, the bipolar index increases, reflecting modifications in the semiconductive behavior. Consequently, the point defect concentration within the passive film decreases, causing a reduction in passive current density and a rise in polarization resistance. Full article
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14 pages, 12121 KB  
Article
Influence of Cold Metal Transfer Parameters on Weld Bead Geometry, Mechanical Properties, and Corrosion Performance of Dissimilar Aluminium Alloys
by Balram Yelamasetti, Mohammed Zubairuddin, Sri Phani Sushma I, Mohammad Faseeulla Khan, Syed Quadir Moinuddin and Hussain Altammar
Crystals 2025, 15(8), 722; https://doi.org/10.3390/cryst15080722 - 13 Aug 2025
Cited by 1 | Viewed by 638
Abstract
Aluminium alloys are known for their high strength-to-weight-ratio offering a wide range of applications in the aerospace and automotive industries. However, challenges exist like porosity, oxidation, solidification shrinkage, hot cracking, etc., in joining aluminium alloys. To address these challenges, there is a necessity [...] Read more.
Aluminium alloys are known for their high strength-to-weight-ratio offering a wide range of applications in the aerospace and automotive industries. However, challenges exist like porosity, oxidation, solidification shrinkage, hot cracking, etc., in joining aluminium alloys. To address these challenges, there is a necessity to understand the process parameters for the welding/joining of aluminium alloys. The present study aims to investigate the effect of cold metal transfer (CMT) welding process parameters (i.e., welding speed and wire feed rate) on mechanical properties for dissimilar AA6061-AA6082 alloys weld joints. Two different welding conditions viz. CMT1 (speed: 0.5 m/min with feed: 5 m/min) and CMT2 (speed: 0.3 m/min with feed: 3 m/min), were considered. The weldments were deployed for testing different mechanical properties such as tensile, impact, hardness, corrosion tests and bead profile geometries. The results reveal that CMT1 has better mechanical properties (tensile_233 MPa; impact_8 J; corrosion rate_0.01368 mm/year) than CMT2, showing the welding speed and wire feed rate play a significant role in the joint performance. The heat affected zone and fusion zone are narrow for CMT1 when compared with CMT2. The present study provides insights into the CMT process and dissimilar joining of aluminium alloys that might be helpful for additive manufacturing of dissimilar aluminium alloys as future research directions. Full article
(This article belongs to the Special Issue Advanced Welding and Additive Manufacturing)
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13 pages, 2972 KB  
Article
Investigation of Electrical Conduction Mechanisms in Silicone Rubber—Bismuth Ferrite Composites
by Cristian Casut, Daniel Ursu, Marinela Miclau, Iosif Malaescu and Catalin Nicolae Marin
Crystals 2025, 15(8), 721; https://doi.org/10.3390/cryst15080721 - 10 Aug 2025
Viewed by 564
Abstract
Three composite materials, made by inserting the same amount of BiFeO3/Bi25FeO40 powders (each powder having a different concentration of the secondary phase, Bi25FeO40: 10%, 20%, and 30%) into a silicone rubber (SR) matrix, were [...] Read more.
Three composite materials, made by inserting the same amount of BiFeO3/Bi25FeO40 powders (each powder having a different concentration of the secondary phase, Bi25FeO40: 10%, 20%, and 30%) into a silicone rubber (SR) matrix, were investigated to understand their electrical properties. Electrical conductivity measurements of the composite samples were carried out over a frequency range from 0.5 kHz to 2 MHz. The resulting conductivity spectra revealed two distinct regions: a low-frequency plateau corresponding to DC conductivity and a high-frequency region where AC conductivity increases with frequency. Some key electrical parameters, such as DC conductivity and band gap energy, were calculated using these measurements. An increase in Bi25FeO40 concentration resulted in a rise in DC conductivity from 5.61 × 10−5 S/m to 7.67 × 10−5 S/m across the composite samples. To gain further insight into the mechanisms of charge transport, both Jonscher’s universal response and the correlated barrier hopping (CBH) model were applied. The polaron model was also used to calculate the energy barrier for electrical conduction, but for higher temperatures (where the samples exhibit conductor behavior). The last part of the study was an aging analysis that showed a degradation of the investigated sample, as reflected by a decline in their conductive properties over time. Having no endothermic or exothermic events in the DTA curves, it is clear that the observed variation in conductive properties is not related to phase transitions, but it can be attributed to microstructural mechanisms, such as defects, microcracks, or structural disorders. These results can help in designing composite materials with desirable conductive properties by optimizing their filler concentration and processing conditions. Full article
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12 pages, 2332 KB  
Article
High-Pressure Behavior and Thermal Stability of Water-Bearing TiO2-II Formed by Phase Transition of Natural Rutile
by Xiaofeng Lu, Shuo Qu, Yuanze Ouyang, Yifan Cao, Meiting Fu, Jinpu Liu and Li Zhang
Crystals 2025, 15(8), 720; https://doi.org/10.3390/cryst15080720 - 10 Aug 2025
Viewed by 553
Abstract
In situ high-pressure Raman spectroscopy (up to 38 GPa) and thermal stability analysis (up to 900 °C) based on Raman and infrared spectroscopy were performed on water-bearing TiO2-II. The samples were synthesized from natural rutile through pressure-induced phase transition experiments. The [...] Read more.
In situ high-pressure Raman spectroscopy (up to 38 GPa) and thermal stability analysis (up to 900 °C) based on Raman and infrared spectroscopy were performed on water-bearing TiO2-II. The samples were synthesized from natural rutile through pressure-induced phase transition experiments. The results demonstrate that at ambient temperature, water-bearing TiO2-II transforms into akaogiite at 12–15 GPa, which is higher than the phase-transition pressure reported in previous studies for anhydrous TiO2-II samples transforming to akaogiite (approximately 10 GPa). Hydroxyl groups at different positions within the TiO2-II structure exhibit distinct thermal stabilities. Although the water-bearing TiO2-II sample underwent partial dehydration between 300 and 400 °C under atmospheric pressure, the majority of the hydroxyl content persisted at higher temperatures (even after the phase transition from TiO2-II to rutile). At ambient pressure, water-bearing TiO2-II transforms to rutile at 500–600 °C, which is significantly lower than the previously reported transition temperature (730 °C) for anhydrous TiO2-II. The partial dehydration of water-bearing TiO2-II during heating may account for the phase transition occurring at a reduced temperature. Full article
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8 pages, 1880 KB  
Article
Study of GaN Thick Films Grown on Different Nitridated Ga2O3 Films
by Xin Jiang, Yuewen Li, Zili Xie, Tao Tao, Peng Chen, Bin Liu, Xiangqian Xiu, Rong Zhang and Youdou Zheng
Crystals 2025, 15(8), 719; https://doi.org/10.3390/cryst15080719 - 9 Aug 2025
Viewed by 451
Abstract
In this paper, various Ga2O3 films, including amorphous Ga2O3 films, β-Ga2O3, and α-Ga2O3 epitaxial films, have been nitridated and converted to single-crystalline GaN layers on the surface. Although the original [...] Read more.
In this paper, various Ga2O3 films, including amorphous Ga2O3 films, β-Ga2O3, and α-Ga2O3 epitaxial films, have been nitridated and converted to single-crystalline GaN layers on the surface. Although the original Ga2O3 films are different, all the converted GaN layers exhibit the (002) preferred orientation and the porous morphologies. The ~200 µm GaN thick films have been grown on the nitridated Ga2O3 films using the halide vapor phase epitaxy (HVPE) method. Raman analysis indicates that all the HVPE-GaN films grown on nitridated Ga2O3 films are almost stress-free. An obvious GaN porous layer/Ga2O3 structure has been observed in the interface between GaN thick films and sapphire substrates. The porous GaN layers can be used as promising templates for the preparation of free-standing GaN substrates. Full article
(This article belongs to the Special Issue Recent Advances in III-Nitride Semiconductors and Correlated Wide Bandgap Semiconductors, 2nd Edition)
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14 pages, 3205 KB  
Article
Typomorphic Characterization and Geological Significance of Megacrystalline Uraninite in the Haita Area, Kangdian Region, Southwestern China
by Minghui Yin, Zhengqi Xu, Bo Xie, Chengjiang Zhang and Jian Yao
Crystals 2025, 15(8), 718; https://doi.org/10.3390/cryst15080718 - 8 Aug 2025
Viewed by 513
Abstract
Megacrystalline uraninite within Neoproterozoic migmatites in the Haita area of the Kangdian region of China provides a unique condition for the investigation of uraninite typomorphism under high-temperature conditions. The present study represents the first systematic characterization of the typomorphic signatures and genetic significance [...] Read more.
Megacrystalline uraninite within Neoproterozoic migmatites in the Haita area of the Kangdian region of China provides a unique condition for the investigation of uraninite typomorphism under high-temperature conditions. The present study represents the first systematic characterization of the typomorphic signatures and genetic significance of megacrystalline uraninite via optical microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XRS), and electron probe microanalysis (EPMA). The results show that uranium mineralization occurs as euhedral megacrystalline uraninite (black grains ≤ 10 mm) hosted in quartz veins, exhibiting frequent rhombic dodecahedral and subordinate cubic–octahedral morphologies. The paragenetic assemblage is quartz–uraninite–titanite–apatite–molybdenite. The investigated uraninite is characterized by elevated unit-cell parameters and a reduced oxygen index, with complex chemical compositions enriched in ThO2 and Y2O3. These typomorphic characteristics indicate crystallization under high-temperature reducing conditions with gradual cooling. Post-crystallization tectonic fragmentation and uplift-facilitated oxidation occur, generating secondary uranium minerals with concentric color zonation (orange–red to yellow–green halos). Mineralization was jointly controlled by migmatization and late-stage tectonism, with the breakup of the Rodinia supercontinent serving as the key driver of fluid mobilization and ore deposition. The data materialized in the present study improve our knowledge about uranium mineralization during continental breakup events. Full article
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24 pages, 4914 KB  
Article
Research on the Production of Methyltrioxorhenium and Heterogenous Catalysts from Waste Materials
by Joanna Malarz, Karolina Goc, Mateusz Ciszewski, Karolina Pianowska, Patrycja Wróbel, Łukasz Hawełek, Dorota Kopyto and Katarzyna Leszczyńska-Sejda
Crystals 2025, 15(8), 717; https://doi.org/10.3390/cryst15080717 - 8 Aug 2025
Viewed by 599
Abstract
This paper presents the research results on the synthesis of rhenium catalysts MTO, Re2O7/Al2O3, and M-Re2O7/Al2O3 (where M = Ni, Ag, Co, Cu) from rhenium compounds (ammonium perrhenate, [...] Read more.
This paper presents the research results on the synthesis of rhenium catalysts MTO, Re2O7/Al2O3, and M-Re2O7/Al2O3 (where M = Ni, Ag, Co, Cu) from rhenium compounds (ammonium perrhenate, perrhenic acid, nickel(II) perrhenate, cobalt(II) perrhenate, zinc perrhenate, silver perrhenate, and copper(II) perrhenate) derived from waste materials. Methyltrioxorhenium (MTO) was obtained from silver perrhenate with a yield of over 80%, whereas when using nickel(II), cobalt(II), and zinc perrhenates, the product was contaminated with tin compounds and the yield did not exceed 17%. The Re2O7/Al2O3 and M-Re2O7/Al2O3 catalysts were obtained from the above-mentioned rhenium compounds. Alumina obtained in a calcination process of aluminum nitrate nonahydrate was used as a support. The catalysts were characterized in terms of their chemical and phase composition and physicochemical properties. Catalytic activity in model reactions, such as cyclohexene epoxidation and hex-1-ene homometathesis, was also studied. MTO obtained from silver perrhenate showed >70% activity in the epoxidation reaction, thus surpassing commercial MTO (1.0 mol% MTO, room temperature, and reaction time—2 h). Ag-Re2O7/Al2O3, Cu-Re2O7/Al2O3, and H-Re2O7/Al2O3 catalysts were inactive, while Co-Re2O7/Al2O3 and Ni-Re2O7/Al2O3 showed low activity (<43%) in the hex-1-ene homometathesis reaction. Only Re2O7/Al2O3 catalysts achieved >70% activity in this reaction (2.5 wt% Re, room temperature, and reaction time—2 h). The results indicate the potential of using rhenium compounds derived from waste materials to synthesize active catalysts for chemical processes. Full article
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