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Crystals, Volume 15, Issue 8 (August 2025) – 9 articles

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18 pages, 4490 KiB  
Article
Tandem Neural Network Based Design of Acoustic Metamaterials for Low-Frequency Vibration Reduction in Automobiles
by Jianjiao Deng, Jiawei Wu, Xi Chen, Xinpeng Zhang, Shoukui Li, Yu Song, Jian Wu, Jing Xu, Shiqi Deng and Yudong Wu
Crystals 2025, 15(8), 676; https://doi.org/10.3390/cryst15080676 - 24 Jul 2025
Abstract
Automotive NVH (Noise, Vibration, and Harshness) performance significantly impacts driving comfort and traffic safety. Vehicles exhibiting superior NVH characteristics are more likely to achieve consumer acceptance and enhance their competitiveness in the marketplace. In the development of automotive NVH performance, traditional vibration reduction [...] Read more.
Automotive NVH (Noise, Vibration, and Harshness) performance significantly impacts driving comfort and traffic safety. Vehicles exhibiting superior NVH characteristics are more likely to achieve consumer acceptance and enhance their competitiveness in the marketplace. In the development of automotive NVH performance, traditional vibration reduction methods have proven to be mature and widely implemented. However, due to constraints related to size and weight, these methods typically address only high-frequency vibration control. Consequently, they struggle to effectively mitigate vehicle body and component vibration noise at frequencies below 200 Hz. In recent years, acoustic metamaterials (AMMs) have emerged as a promising solution for suppressing low-frequency vibrations. This development offers a novel approach for low-frequency vibration control. Nevertheless, conventional design methodologies for AMMs predominantly rely on empirical knowledge and necessitate continuous parameter adjustments to achieve desired bandgap characteristics—an endeavor that entails extensive calculations and considerable time investment. With advancements in machine learning technology, more efficient design strategies have become feasible. This paper presents a tandem neural network (TNN) specifically developed for the design of AMMs. The trained neural network is capable of deriving both the bandgap characteristics from the design parameters of AMMs as well as deducing requisite design parameters based on specified bandgap targets. Focusing on addressing low-frequency vibrations in the back frame of automobile seats, this method facilitates the determination of necessary AMMs design parameters. Experimental results demonstrate that this approach can effectively guide AMMs designs with both speed and accuracy, and the designed AMMs achieved an impressive vibration attenuation rate of 63.6%. Full article
(This article belongs to the Special Issue Metamaterials and Their Devices, Second Edition)
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10 pages, 1512 KiB  
Article
Research on the Efficient Desilication Process of Low-Grade Bauxite in Guangxi
by Guoxian Hu, Anmin Li, An Xia, Dongjie Zhang, Liwen Pan, Xiaolian Zhao and Xingzhi Pang
Crystals 2025, 15(8), 675; https://doi.org/10.3390/cryst15080675 - 24 Jul 2025
Abstract
With the continuous exploitation of bauxite mineral resources, Guangxi bauxite faces many difficulties in alumina production due to its characteristics of high silicon content, high iron content, and a low Al-Si ratio. In view of this, this study is closely related to the [...] Read more.
With the continuous exploitation of bauxite mineral resources, Guangxi bauxite faces many difficulties in alumina production due to its characteristics of high silicon content, high iron content, and a low Al-Si ratio. In view of this, this study is closely related to the key link of bauxite pre-desiliconization and strives to break free from the status quo to improve the aluminum/silicon ratio and help optimize the subsequent alumina-refining process. In the work presented in this paper, the unique mineralogy of Guangxi bauxite was comprehensively considered, covering its complex mineral composition and fine distribution characteristics. The barium hydroxide pre-desilication technology was first used for in-depth experimental exploration, and the silicon removal efficiency under different working conditions was systematically compared. The system compared the silicon removal effect and the associated aluminum loss under different working conditions. The results of this study will lay a solid foundation for the rational and efficient development of bauxite in Guangxi, which is expected to reduce the cost of alumina production, improve the economic benefits for the Guangxi aluminum industry, simultaneously strengthen the efficiency of resource recycling, accelerate the sustainable development of the industry, and provide a useful reference example for subsequent similar studies. Full article
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16 pages, 29184 KiB  
Article
Dehydration-Induced Space Group Transition Triggers Conformational Changes in Protein Structure
by Ki Hyun Nam
Crystals 2025, 15(8), 674; https://doi.org/10.3390/cryst15080674 - 24 Jul 2025
Abstract
Protein packing within crystal lattices plays a critical role in determining molecular flexibility; therefore, the observed conformation and flexibility of protein side chains can vary depending on the crystal space group. Protein crystal dehydration affects crystal lattice mosaicity, which can either reduce crystal [...] Read more.
Protein packing within crystal lattices plays a critical role in determining molecular flexibility; therefore, the observed conformation and flexibility of protein side chains can vary depending on the crystal space group. Protein crystal dehydration affects crystal lattice mosaicity, which can either reduce crystal quality or enhance X-ray diffraction intensity. It also often alters the crystal lattice, leading to space group transition. Accordingly, dehydration-induced space group transitions could theoretically offer an alternative when there are experimental limitations obstructing the obtainment of diverse crystal forms. However, this remains underexplored experimentally. Here, a dehydration-induced space group transition was explored to observe different conformations and flexibilities of the protein structure. Xylanase GH11 crystals from Thermoanaerobacterium saccharolyticum (TsaGH11) were air-dehydrated, and their structure at room temperature was determined. Upon dehydration, the space group of the TsaGH11 crystal changed from tetragonal to orthorhombic, affecting the protein–protein interfaces within the crystal lattice. The dehydrated crystal structure of TsaGH11 revealed multiple conformations of residues involved in substrate binding and recognition within the substrate-binding cleft. These diverse molecular conformations and flexibilities provide significant and previously unrevealed structural information for TsaGH11. This approach demonstrates the potential of dehydration-induced space group transitions to reveal diverse protein conformations, offering valuable insights into molecular properties and functions. Full article
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14 pages, 3417 KiB  
Article
Structural Comparison of Three N-(4-Methoxyphenyl)-Nitrobenzenesulfonamide Derivatives
by Mark Oblazny and Christhoper G. Hamaker
Crystals 2025, 15(8), 673; https://doi.org/10.3390/cryst15080673 - 23 Jul 2025
Abstract
The series of all three N-(4-methoxyphenyl)-nitrobenzenesulfonamides has been synthesized and their crystal structures analyzed. The bond lengths and angles are all very similar, only the C-S-N-C torsion angles are significantly different in the three molecules, leading to different orientations of the phenyl [...] Read more.
The series of all three N-(4-methoxyphenyl)-nitrobenzenesulfonamides has been synthesized and their crystal structures analyzed. The bond lengths and angles are all very similar, only the C-S-N-C torsion angles are significantly different in the three molecules, leading to different orientations of the phenyl rings in the molecules. All three molecules exhibit N–HO hydrogen bonds with the sulfonamide group; however, in only two of the three is the acceptor an oxygen atom on the sulfonamide group. In the third, the acceptor oxygen is the methoxy oxygen atom. Compound A forms an infinite three-dimensional network, compound B exhibits ladder-shaped sheets, and C shows infinite sheets that are fairly planar. Overall, the differences in overall intermolecular interactions appear to be driven by packing rather than by the overall shapes of the molecules themselves. Full article
(This article belongs to the Section Crystal Engineering)
15 pages, 2825 KiB  
Article
Effects of Pressure on Hydrogen Diffusion Behaviors in Corundum
by Shun-Feng Yan, Lin Li, Xiao Dong, Xiao-Wei Li, Mao-Wen Yuan and Sheng-Rong Li
Crystals 2025, 15(8), 672; https://doi.org/10.3390/cryst15080672 - 23 Jul 2025
Abstract
Hydrogen, as the smallest atom and a key component of water, can penetrate minerals in various forms (e.g., atoms, molecules), significantly influencing their properties. The hydrogen diffusion behavior in corundum (α-Al2O3) under high pressure was systematically investigated using the [...] Read more.
Hydrogen, as the smallest atom and a key component of water, can penetrate minerals in various forms (e.g., atoms, molecules), significantly influencing their properties. The hydrogen diffusion behavior in corundum (α-Al2O3) under high pressure was systematically investigated using the DFT + NEB method. The results indicate that H atoms tend to aggregate into H2 molecules within corundum under both ambient and high-pressure conditions. However, hydrogen predominantly migrates in its atomic form (H) under both low- and high-pressure environments. The energy barriers for H and H2 diffusion increase with pressure, and hydrogen diffusion weakens the chemical bonds nearby. Using the Arrhenius equation, we calculated the diffusion coefficient of H in corundum, which increases with temperature but decreases with pressure. On geological time scales, hydrogen diffusion is relatively slow, potentially resulting in a heterogeneous distribution of water in the lower mantle. These findings provide novel insights into hydrogen diffusion mechanisms in corundum under extreme conditions, with significant implications for hydrogen behavior in mantle minerals at high pressures. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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35 pages, 1752 KiB  
Review
Recent Advances in Biodegradable Magnesium Alloys for Medical Implants: Evolution, Innovations, and Clinical Translation
by Mykyta Aikin, Vadim Shalomeev, Volodymyr Kukhar, Andrii Kostryzhev, Ihor Kuziev, Viktoriia Kulynych, Oleksandr Dykha, Volodymyr Dytyniuk, Oleksandr Shapoval, Alvydas Zagorskis, Vadym Burko, Olha Khliestova, Viacheslav Titov and Oleksandr Hrushko
Crystals 2025, 15(8), 671; https://doi.org/10.3390/cryst15080671 - 23 Jul 2025
Abstract
Biodegradable magnesium alloys have emerged as promising alternatives to permanent metallic implants due to their unique combination of mechanical compatibility with bone and complete resorption, addressing the persistent issues of stress shielding and secondary removal surgeries. This review critically examines the historical development [...] Read more.
Biodegradable magnesium alloys have emerged as promising alternatives to permanent metallic implants due to their unique combination of mechanical compatibility with bone and complete resorption, addressing the persistent issues of stress shielding and secondary removal surgeries. This review critically examines the historical development of magnesium-based biomaterials, highlighting advances in alloy design, manufacturing processes, and surface engineering that now enable tailored degradation and improved clinical performance. Drawing on recent clinical and preclinical studies, we summarize improvements in corrosion resistance, mechanical properties, and biocompatibility that have supported the clinical translation of magnesium alloys across a variety of orthopedic and emerging medical applications. However, challenges remain, including unpredictable in vivo degradation kinetics, limited long-term safety data, lack of standardized testing protocols, and ongoing regulatory uncertainties. We conclude that while magnesium-based biomaterials have advanced from experimental concepts to clinically validated solutions, further progress in personalized degradation control, real-time monitoring, and harmonized regulatory frameworks is needed to fully realize their transformative clinical potential. Full article
(This article belongs to the Special Issue Development of Light Alloys and Their Applications)
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24 pages, 1483 KiB  
Review
Towards AZO Thin Films for Electronic and Optoelectronic Large-Scale Applications
by Elena Isabela Bancu, Valentin Ion, Stefan Antohe and Nicu Doinel Scarisoreanu
Crystals 2025, 15(8), 670; https://doi.org/10.3390/cryst15080670 - 23 Jul 2025
Abstract
Transparent conductive oxides (TCOs) have become essential components in a broad range of modern devices, including smartphones, flat-panel displays, and photovoltaic cells. Currently, indium tin oxide (ITO) is used in approximately 90% of these devices. However, ITO prices continue to rise due to [...] Read more.
Transparent conductive oxides (TCOs) have become essential components in a broad range of modern devices, including smartphones, flat-panel displays, and photovoltaic cells. Currently, indium tin oxide (ITO) is used in approximately 90% of these devices. However, ITO prices continue to rise due to the limited supply of indium (In), making the development of alternative materials for TCOs indispensable. Therefore, this study highlights the latest advances in creating new, affordable materials, with a focus on aluminum-doped zinc oxide (AZO). Over the last few decades, this material has been widely studied to improve its physical properties, particularly its low electrical resistivity, which can affect the performance of various devices. Now, it is close to replacing ITO due to several advantages including cost-effectiveness, stability under hydrogen plasma, low processing temperatures, and lack of toxicity. Besides that, in comparison to other TCOs such as IZO, IGZO, or IZrO, AZO achieved a low electrical resistivity (10−5 ohm cm) while maintaining a high transparency across the visible spectrum (over 85%). Additionally, due to the increasing development of technologies utilizing such materials, it is essential to develop more effective techniques for producing TCOs on a larger scale. Additionally, due to the increasing development of technologies utilizing such materials, it is essential to develop more effective techniques for producing TCOs on a larger scale. This review emphasizes the potential of AZO as a cost-effective and scalable alternative to ITO, highlighting key advancements in deposition techniques such as pulsed laser deposition (PLD). Full article
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13 pages, 1952 KiB  
Article
Real-Time Dose Measurement in Brachytherapy Using Scintillation Detectors Based on Ce3+-Doped Garnet Crystals
by Sandra Witkiewicz-Łukaszek, Bogna Sobiech, Janusz Winiecki and Yuriy Zorenko
Crystals 2025, 15(8), 669; https://doi.org/10.3390/cryst15080669 - 23 Jul 2025
Abstract
Conventional detectors based on ionization chambers, semiconductors, or thermoluminescent materials generally cannot be used to verify the in vivo dose delivered during brachytherapy treatments with γ-ray sources. However, certain adaptations and alternative methods, such as the use of miniaturized detectors or other specialized [...] Read more.
Conventional detectors based on ionization chambers, semiconductors, or thermoluminescent materials generally cannot be used to verify the in vivo dose delivered during brachytherapy treatments with γ-ray sources. However, certain adaptations and alternative methods, such as the use of miniaturized detectors or other specialized techniques, have been explored to address this limitation. One approach to solving this problem involves the use of dosimetric materials based on efficient scintillation crystals, which can be placed in the patient’s body using a long optical fiber inserted intra-cavernously, either in front of or next to the tumor. Scintillation crystals with a density close to that of tissue can be used in any location, including the respiratory tract, as they do not interfere with dose distribution. However, in many cases of radiation therapy, the detector may need to be positioned behind the target. In such cases, the use of heavy, high-density, and high-Zeff scintillators is strongly preferred. The delivered radiation dose was registered using the radioluminescence response of the crystal scintillator and recorded with a compact luminescence spectrometer connected to the scintillator via a long optical fiber (so-called fiber-optic dosimeter). This proposed measurement method is completely non-invasive, safe, and can be performed in real time. To complete the abovementioned task, scintillation detectors based on YAG:Ce (ρ = 4.5 g/cm3; Zeff = 35), LuAG:Ce (ρ = 6.75 g/cm3; Zeff = 63), and GAGG:Ce (ρ = 6.63 g/cm3; Zeff = 54.4) garnet crystals, with different densities ρ and effective atomic numbers Zeff, were used in this work. The results obtained are very promising. We observed a strong linear correlation between the dose and the scintillation signal recorded by the detector system based on these garnet crystals. The measurements were performed on a specially prepared phantom in the brachytherapy treatment room at the Oncology Center in Bydgoszcz, where in situ measurements of the applied dose in the 0.5–8 Gy range were performed, generated by the 192Ir (394 keV) γ-ray source from the standard Fexitron Elektra treatment system. Finally, we found that GAGG:Ce crystal detectors demonstrated the best figure-of-merit performance among all the garnet scintillators studied. Full article
(This article belongs to the Special Issue Recent Advances in Scintillator Materials)
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11 pages, 2412 KiB  
Article
Lab- and Large-Scale Hydrothermal Synthesis of Vanadium Dioxide Thermochromic Powder
by Emmanouil Gagaoudakis, Eleni Mantsiou, Leila Zouridi, Elias Aperathitis and Vasileios Binas
Crystals 2025, 15(8), 668; https://doi.org/10.3390/cryst15080668 - 23 Jul 2025
Abstract
Vanadium dioxide (VO2) is a phase-change material of great importance due to its thermochromic properties, which make it a potential candidate for energy-saving applications. In this work, a comparative study between VO2 thermochromic films prepared from powders synthesized by either [...] Read more.
Vanadium dioxide (VO2) is a phase-change material of great importance due to its thermochromic properties, which make it a potential candidate for energy-saving applications. In this work, a comparative study between VO2 thermochromic films prepared from powders synthesized by either a lab-scale hydrothermal autoclave or a large-scale hydrothermal reactor is presented. In both cases, the as-obtained material, after the hydrothermal step, was subsequently annealed at 700 °C under a nitrogen atmosphere, in order to obtain the monoclinic VO2(M) thermochromic phase. The VO2 powder prepared in the large-scale hydrothermal reactor exhibited a critical transition temperature of 54 °C with a hysteresis width of 9 °C, while for the one prepared in the lab-scale autoclave, the respective values were 62 °C and 5 °C. Despite these differences, the prepared films showed similar thermochromic performance with the lab-scale material displaying a 17% IR (InfraRed), switching at 2000 nm upon heating, and a transmittance solar modulation of 11%, compared to 17% and 9%, respectively, for the large-scale material. Moreover, both films appeared to have similar luminous transmittance of 44% and 46%, respectively, at room temperature (25 °C). These results showcase the potential for scaling up the hydrothermal synthesis of VO2, resulting in films with similar thermochromic performance to those from lab-scale fabrication. Full article
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