Crystals

18 pages, 6306 KiB

Open AccessArticle

Machine-Learning-Driven Analysis of Wear Loss and Frictional Behavior in Magnesium Hybrid Composites

by Barun Haldar, Hillol Joardar, Arpan Kumar Mondal, Nashmi H. Alrasheedi, Rashid Khan and Murugesan P. Papathi

Crystals 2025, 15(5), 452; https://doi.org/10.3390/cryst15050452 (registering DOI) - 11 May 2025

Abstract

The wear loss and frictional characteristics of magnesium-based hybrid composites reinforced with boron carbide (B₄C) particles and graphite filler were the main subjects of the investigation. Key parameters, including reinforcement content (0–10 wt%), applied load (5–30 N), sliding speed (0.5–3 m/s), [...] Read more.

The wear loss and frictional characteristics of magnesium-based hybrid composites reinforced with boron carbide (B₄C) particles and graphite filler were the main subjects of the investigation. Key parameters, including reinforcement content (0–10 wt%), applied load (5–30 N), sliding speed (0.5–3 m/s), and sliding distance (500–3000 m), were varied. Data-driven machine learning (ML) algorithms were utilized to identify complex patterns and predict relationships between input variables and output responses. Five distinct machine learning algorithms, Artificial Neural Network (ANN), Random Forest (RF), K-Nearest Neighbor (KNN), Gradient Boosting Machine (GBM), and Support Vector Machine (SVM), were employed to analyze experimental tribological data for predicting wear loss and coefficients of friction (COFs). The performance evaluation showed that ML models effectively predicted friction behavior and wear behavior of magnesium-based hybrid composites using tribological test data. A comparison of model performances revealed that the Gradient Boosting Machine (GBM) provided superior accuracy compared to other machine learning models in predicting both wear loss and the coefficient of friction. Additionally, feature importance analysis indicated that the graphite weight percentage was the most significant influence in predicting the coefficient of friction and wear loss characteristics. Full article

(This article belongs to the Special Issue Structural and Characterization of Composite Materials)

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15 pages, 4851 KiB

Open AccessArticle

Shape-Engineering and Mechanism Investigation of AgCl Microcrystals

by Chunli Cai, Qian Wang, Changsheng Yin, Xuhuan Li, Rong Yang, Xiaodong Shen and Wenbo Xin

Crystals 2025, 15(5), 451; https://doi.org/10.3390/cryst15050451 (registering DOI) - 10 May 2025

Abstract

: AgCl microcrystals are used in visible light photocatalysis. However, their properties depend strongly on the morphology of the crystals and the degree of exposure of the crystal planes. Despite extensive research conducted on the synthesis of AgCl microcrystals, the majority of existing [...] Read more.

: AgCl microcrystals are used in visible light photocatalysis. However, their properties depend strongly on the morphology of the crystals and the degree of exposure of the crystal planes. Despite extensive research conducted on the synthesis of AgCl microcrystals, the majority of existing studies have focused on the stable growth of crystals. The role of Cl⁻ ions concentration as a key factor controlling the microcrystals morphology has not been fully explored, which limits the precise tuning of the morphology of AgCl microcrystals. In this study, AgCl microcrystals with controllable morphology are successfully synthesized by a facile solvothermal method. During the preparation process, ethylene glycol (EG) is utilized as a solvent, while polyvinylpyrrolidone (PVP) is employed as a surfactant. We systematically investigate the etching mechanism of AgCl microcrystals by analyzing the effect of sodium chloride (NaCl) concentration on their morphology. This investigation involves the integration of diverse characterization methods, including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and geometrical struc-ture analysis. The results demonstrate that Cl⁻ functions as both a surfactant, thereby promoting the nucleation of cubic microcrystals, and as an etchant, selectively etching the crystal surface. The order of selective etching on the crystal surface follows (100) planes > (110) planes > (111) planes. Based on this new mechanism, AgCl microcrystals with various morphologies, such as cube, octopod and dendrite, are successfully prepared, which provides a new idea for the precise design of noble metal halide microcrystals. Full article

(This article belongs to the Section Crystal Engineering)

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14 pages, 914 KiB

Open AccessArticle

Numerical Insights into Wide-Angle, Phase-Controlled Optical Absorption in a Single-Layer Vanadium Dioxide Structure

by Abida Parveen, Ahsan Irshad, Deepika Tyagi, Mehboob Alam, Shakeel Ahmed, Keyu Tao and Zhengbiao Ouyang

Crystals 2025, 15(5), 450; https://doi.org/10.3390/cryst15050450 (registering DOI) - 10 May 2025

Abstract

Vanadium dioxide (VO

_{2}

) is a well-known phase-change material that exhibits a thermally driven insulator-to-metal transition (IMT) near 68 °C, leading to significant changes in its electrical and optical properties. This transition is governed by structural modifications in the VO

_{2}

crystal [...] Read more.

Vanadium dioxide (VO

_{2}

) is a well-known phase-change material that exhibits a thermally driven insulator-to-metal transition (IMT) near 68 °C, leading to significant changes in its electrical and optical properties. This transition is governed by structural modifications in the VO

_{2}

crystal lattice, enabling dynamic control over absorption, reflection, and transmission. Despite its promising tunability, VO

_{2}

-based optical absorbers face challenges such as a narrow IMT temperature window, intrinsic optical losses, and fabrication complexities associated with multilayer designs. In this work, we propose and numerically investigate a single-layer VO

_{2}

-based optical absorber for the visible spectrum using full-wave electromagnetic simulations. The proposed absorber achieves nearly 95% absorption at 25 °C (insulating phase), which drops below 5% at 80 °C (metallic phase), demonstrating exceptional optical tunability. This behavior is attributed to VO

_{2}

’s high refractive index in the insulating state, which enhances resonant light trapping. Unlike conventional multilayer absorbers, our single-layer VO

_{2}

design eliminates structural complexity, simplifying fabrication and reducing material costs. These findings highlight the potential of VO

_{2}

-based crystalline materials for tunable and energy-efficient optical absorption, making them suitable for adaptive optics, smart windows, and optical switching applications. The numerical results presented in this study contribute to the ongoing development of crystal-based phase-transition materials for next-generation reconfigurable photonic and optoelectronic devices. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

22 pages, 6877 KiB

Open AccessArticle

Inspection of Bulk Crystals for Quality Control in Crystal Growth: Assessment of High-Energy X-Ray Transmission Topography and Back-Reflection Topography Pinpointed for Physical Vapor Transport-Grown Aluminum Nitride

by Roland Weingärtner, Boris Epelbaum, Andreas Lesnik, Gleb Lukin, Stephan Müller, Leon Schiller, Elke Meissner, Matthias Weisser and Sven Besendörfer

Crystals 2025, 15(5), 449; https://doi.org/10.3390/cryst15050449 - 9 May 2025

Viewed by 109

Abstract

A comprehensive X-ray topography analysis of two selected aluminum nitride (AlN) bulk crystals is presented. We compare surface inspection X-ray topography in back-reflection geometry with high-energy transmission topography in the Lang and Laue configuration using the monochromatic K_α1 excitation wavelength of copper, [...] Read more.

A comprehensive X-ray topography analysis of two selected aluminum nitride (AlN) bulk crystals is presented. We compare surface inspection X-ray topography in back-reflection geometry with high-energy transmission topography in the Lang and Laue configuration using the monochromatic K_α1 excitation wavelength of copper, silver, and tungsten, respectively. A detailed comparison of the results allows the assessment of both the high- and low-energy X-ray topography methods with respect to performance and structural information, giving essential feedback for crystal growth. This is demonstrated for two selected AlN freestanding faceted crystals up to 8 mm in thickness grown in all directions using the physical vapor transport (PVT) method. Structural defects of all facets of the crystals are determined using the X-ray topography in back-reflection geometry. The mean threading dislocation densities are 480 ± 30 cm⁻² for both crystals of either the Al- or N-face. Clustering of dislocations could be observed. The m-facets show the presence of basal plane dislocations and their accumulation as clusters. The integral transmission topographs of the

10 \bar{1} 0

(m-plane) reflection family show that basal plane dislocations of the screw type in

\frac{1}{3} ⟨\bar{1} 2 \bar{1} 0⟩

directions decorate threading dislocation clusters. Three-dimensional section transmission topography reveals that the basal plane dislocation clusters mainly originate at the seed boundary and propagate in the

\frac{1}{3} ⟨\bar{1} 2 \bar{1} 0⟩

direction along the growth front. In newly laterally grown material, the Borrmann effect has been observed for the first time in PVT-grown bulk AlN, indicating very high structural perfection of the crystalline material in this region. This agrees with a low mean FWHM of 10.6 arcsec of the

10 \bar{1} 0

reflection determined through focused high-energy Laue transmission mappings. The latter method also opens the analysis of the

∆ 2 θ

-shift correlated to the residual stress distribution inside the bulk crystal, which is dominated by dislocation clusters. Contrary to Lang transmission topography, the de-focused high-energy Laue transmission penetrates the 8 mm-thick crystal enabling a defect analysis in the bulk. Full article

(This article belongs to the Section Crystal Engineering)

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11 pages, 2623 KiB

Open AccessArticle

Structural Analysis of PlyKp104, a Novel Phage Endoysin

by Jung-Min Choi

Crystals 2025, 15(5), 448; https://doi.org/10.3390/cryst15050448 - 9 May 2025

Viewed by 88

Abstract

Antibiotic resistance has emerged as a critical global public health challenge, prompting increased interest in non-antibiotic antimicrobial strategies such as bacteriophage-derived endolysins. Although endolysins possess strong lytic potential, their application to Gram-negative bacteria remains limited due to the outer membrane barrier. PlyKp104 is [...] Read more.

Antibiotic resistance has emerged as a critical global public health challenge, prompting increased interest in non-antibiotic antimicrobial strategies such as bacteriophage-derived endolysins. Although endolysins possess strong lytic potential, their application to Gram-negative bacteria remains limited due to the outer membrane barrier. PlyKp104 is a recently identified phage-derived endolysin that exhibits lytic activity against Gram-negative bacteria without the aid of membrane permeabilizers. In this study, the crystal structure of PlyKp104 was determined at a resolution of 1.85 Å. PlyKp104 consists solely of a catalytic SLT domain, and structure-based analysis revealed a putative active site and key structural features associated with substrate binding. Comparative analysis with homologous structures suggested that PlyKp104 belongs to lytic transglycosylase family 1. B-factor analysis and hydrophobic interaction mapping indicated that the domain exhibits high structural stability, supported by conserved hydrophobic residues clustered in motifs I and II. During structure determination, an unidentified electron density was consistently observed near a neutral, hydrophobic surface region. Its shape and environment suggest the presence of a lipid-like molecule, implying a potential lipid-binding site. These findings provide structural insight into PlyKp104 and contribute to the understanding of endolysin mechanisms against Gram-negative bacteria, with implications for future protein engineering efforts. Full article

(This article belongs to the Special Issue Crystallography of Enzymes)

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16 pages, 7322 KiB

Open AccessArticle

Structural Study of Thermostable Ginsenoside β-Glucosidase from Caldicellulosiruptor bescii

by Jung-Min Choi

Crystals 2025, 15(5), 447; https://doi.org/10.3390/cryst15050447 - 9 May 2025

Viewed by 117

Abstract

Protopanaxadiol-type ginsenosides, the major bioactive components of Panax ginseng, exhibit diverse pharmacological activities, but suffer from low oral bioavailability due to poor water solubility and membrane permeability. Enzymatic deglycosylation has emerged as an effective strategy to enhance their therapeutic potential; however, most [...] Read more.

Protopanaxadiol-type ginsenosides, the major bioactive components of Panax ginseng, exhibit diverse pharmacological activities, but suffer from low oral bioavailability due to poor water solubility and membrane permeability. Enzymatic deglycosylation has emerged as an effective strategy to enhance their therapeutic potential; however, most glucosidases lack sufficient thermostability for industrial applications. A β-glucosidase from the thermophilic bacterium Caldicellulosiruptor bescii (CbBGL) has demonstrated efficient conversion of major ginsenosides into compound K at elevated temperatures. In this study, the high-resolution crystal structure of CbBGL was determined at 1.9 Å. Structural analysis revealed that CbBGL adopts a classical (α/β)₈ TIM barrel fold and functions as a homodimer. Comparative studies with other glucosidases highlighted structural features contributing to its thermostability, including moderate B-factor distribution and a limited hydrogen bond network. Docking analyses revealed a narrow, inverted conical substrate-binding cleft, which imposes specific binding orientations and underlies the enzyme’s stepwise deglycosylation mechanism. These insights provide a structural basis for CbBGL’s thermal resilience and substrate specificity, offering a valuable platform for the rational engineering of glucosidases in ginsenoside bioconversion processes. Full article

(This article belongs to the Special Issue Crystallography of Enzymes)

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15 pages, 4412 KiB

Open AccessArticle

Evolution of Phonon Spectral Energy Density in Superlattice Structures

by Milad Nasiri and Yan Wang

Crystals 2025, 15(5), 446; https://doi.org/10.3390/cryst15050446 - 9 May 2025

Viewed by 128

Abstract

Superlattices are a distinctive class of artificial nanostructures formed by the periodic stacking of two or more materials. The high density of interfaces in these structures often gives rise to exotic physical properties. In the context of thermal transport, it is well established [...] Read more.

Superlattices are a distinctive class of artificial nanostructures formed by the periodic stacking of two or more materials. The high density of interfaces in these structures often gives rise to exotic physical properties. In the context of thermal transport, it is well established that such interfaces can significantly scatter particle-like phonons while also inducing constructive or destructive interference in wave-like phonons, depending on the relationship between the phonons’ coherence lengths and the superlattice’s period thickness. In this work, we systematically investigate the effect of temperature on the spectral energy density of phonon modes in superlattices. Additionally, we examine how variations in superlattice period thickness influence phonon lifetimes and energy density. Our findings provide critical insights into the spectral phonon properties of superlattices, particularly in terms of their coherence and lifetimes. Full article

(This article belongs to the Special Issue Metamaterials and Their Devices, Second Edition)

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22 pages, 16641 KiB

Open AccessArticle

Features of Electronic Transport Properties in All-Carbon Films Based on Bilayer Graphene and Single-Walled Nanotubes

by Michael M. Slepchenkov, Pavel V. Barkov and Olga E. Glukhova

Crystals 2025, 15(5), 445; https://doi.org/10.3390/cryst15050445 - 9 May 2025

Viewed by 181

Abstract

In this paper, we conduct a detailed in silico study of the role of topological features in the electronic transport properties of all-carbon films. To create all-carbon film supercells, we used AA- and AB-stacked bilayer graphene, as well as (5,5), (6,0), (16,0), (12,6), [...] Read more.

In this paper, we conduct a detailed in silico study of the role of topological features in the electronic transport properties of all-carbon films. To create all-carbon film supercells, we used AA- and AB-stacked bilayer graphene, as well as (5,5), (6,0), (16,0), (12,6), and (8,4) single-walled carbon nanotubes (SWCNTs). For the first time, the simultaneous influence of several topological features on the quantum transport of electrons in graphene–nanotube films are considered. Topological features are understood as the topological type of nanotubes (chiral or achiral), the stacking order in bilayer graphene (AA or AB), and the mutual orientation of bilayer graphene and nanotubes. A characteristic feature of the studied all-carbon films is the presence of electrical conductivity anisotropy. Moreover, depending on the topological features of all-carbon films, the values of electrical resistance can differ by tens of times in different directions of electron transport. The patterns of formation of the profile of the electron transmission function of the studied structural configurations of all-carbon film are established. It is found that the mutual orientation of bilayer graphene and nanotubes plays an important role in the electronic transport properties of all-carbon films. The obtained results make a significant contribution to the understanding of the mechanisms controlling the electrical conductivity properties of all-carbon films at the atomic level. Full article

(This article belongs to the Special Issue Graphene-Based Materials and Applications)

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15 pages, 4952 KiB

Open AccessArticle

Optimized Breakdown Strength and Crystal Structure for Boosting the Energy Storage Performance of Niobate-Based Glass Ceramics via a B-Site Substitution Strategy

by Kexin Gao, Fei Shang, Yaoyi Qin and Guohua Chen

Crystals 2025, 15(5), 444; https://doi.org/10.3390/cryst15050444 - 8 May 2025

Viewed by 164

Abstract

Based on the B-site modification strategy, excellent energy storage properties were achieved in this work by substituting Nb with Ta of the same valence in niobate-based glass ceramics. Ta substitution was found to lead to the transformation of crystal structures, and the space [...] Read more.

Based on the B-site modification strategy, excellent energy storage properties were achieved in this work by substituting Nb with Ta of the same valence in niobate-based glass ceramics. Ta substitution was found to lead to the transformation of crystal structures, and the space point group evolved from the non-centrosymmetric P4bm to the centrosymmetric P4/mbm, resulting in a transition from relaxor ferroelectric to paraelectric glass ceramics. Furthermore, the addition of Ta led to a significant decrease in grain size and interfacial activation energy, as well as an increase in the optical band gap, resulting in a dramatic increase in BDS from 800 kV/cm to 1300 kV/cm. The KBSN-4.0mol%Ta₂O₅ glass ceramic exhibited optimal energy storage properties, including a discharge energy density of ~5.62 J/cm³ and a superfast discharge rate of ~9.7 ns, resulting in an ultrahigh discharge power density of about ~1296.9 MW/cm³ at 1300 kV/cm. Furthermore, this KBSN-Ta glass ceramic also displayed good thermal stability over a temperature range of 20–120 °C, with the W_d decreasing by 9.0% at 600 kV/cm. B-site modification engineering in glass ceramics has proved to be an important way to effectively optimize energy storage performance. Full article

(This article belongs to the Special Issue Advances in Glass-Ceramics)

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13 pages, 2056 KiB

Open AccessArticle

Finding Crystal Orientations in Uniplanar Textures

by Josef Simbrunner, Fabian Gasser, Sanjay John, Ingo Salzmann and Roland Resel

Crystals 2025, 15(5), 443; https://doi.org/10.3390/cryst15050443 - 8 May 2025

Viewed by 117

Abstract

The crystallization of molecular materials on isotropic substrates typically results in a so-called fiber or uniplanar texture that comprises crystallites that share a common fiber axis perpendicular to the substrate surface, but that are azimuthally randomly oriented. The crystallographic characterization of such films [...] Read more.

The crystallization of molecular materials on isotropic substrates typically results in a so-called fiber or uniplanar texture that comprises crystallites that share a common fiber axis perpendicular to the substrate surface, but that are azimuthally randomly oriented. The crystallographic characterization of such films is commonly performed by grazing-incidence X-ray diffraction. Thereby, two-dimensional reciprocal space maps are obtained that incorporate the in-plane component q_xy and the out-of-plane component q_z for each diffraction peak. The exact position of each diffraction peak depends on the crystallographic lattice and on the orientation of the unit cell relative to the substrate surface. The unit cell orientation can be characterized either by two rotation angles or by the Miller indices of the crystallographic plane (contact plane) parallel to the substrate surface. Equations are derived that allow the calculation of these orientation parameters and describe the relations between them. Depending on the crystallographic system of the underlying unit cell and its contact plane, manifold possible orientations may exist due to the multiplicity of planes contributing to the same reflections. Examples based on molecular crystals of pentacenequinone, diindenoperylene, and binaphthalene are discussed, which are illustrative examples comprising triclinic, monoclinic, and tetragonal unit cells having two, four, and sixteen possible crystal orientations, respectively. Full article

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11 pages, 4787 KiB

Open AccessArticle

From Type II to Z-Scheme: A DFT Study of Enhanced Water Splitting in the SGa₂Se/TeMoS Heterojunction

by Fan Yang, Marie-Christine Record and Pascal Boulet

Crystals 2025, 15(5), 442; https://doi.org/10.3390/cryst15050442 - 7 May 2025

Viewed by 55

Abstract

Harnessing solar energy for photocatalytic water splitting and hydrogen fuel production necessitates the development of advanced photocatalysts with broad solar spectrum absorption and efficient electron-hole separation. In this study, we systematically explore the potential of the SGa₂Se/TeMoS heterojunction as a water-splitting [...] Read more.

Harnessing solar energy for photocatalytic water splitting and hydrogen fuel production necessitates the development of advanced photocatalysts with broad solar spectrum absorption and efficient electron-hole separation. In this study, we systematically explore the potential of the SGa₂Se/TeMoS heterojunction as a water-splitting photocatalyst using first-principles calculations. Our results indicate that while the heterojunction exhibits type-II band alignment, its band edge positions are inadequate for initiating water redox reactions. To overcome this limitation, we successfully engineered a Z-scheme SGa₂Se/Zr/TeMoS heterojunction by incorporating a Zr layer to modulate the charge transfer mechanism between the SGa₂Se and TeMoS layers. The potential positions of the HER and OER in this Z-scheme heterojunction overcome the limitation of the bandgap on water decomposition, allowing the optimized heterojunction to exhibit suitable band edge positions for water splitting across a wide pH range (0 ≤ pH ≤ 11.3), from acidic to weakly basic conditions. Additionally, the heterojunction exhibits exceptional light absorption capabilities across the entire spectrum, particularly in the infrared and visible regions, which greatly enhances the utilization of solar energy and highlights its potential as an efficient broad-spectrum photocatalyst for water splitting. Full article

(This article belongs to the Special Issue Advanced Materials for Applications in Water Splitting)

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16 pages, 8910 KiB

Open AccessArticle

Influence of Synthesis Conditions on the Monoclinic Structure Formation of Gd_0.85−yLa_yPO₄:15%Eu and Luminescent Properties

by Darius Budrevičius, Eglė Buzaitytė, Kęstutis Mažeika and Ramūnas Skaudžius

Crystals 2025, 15(5), 441; https://doi.org/10.3390/cryst15050441 - 6 May 2025

Viewed by 162

Abstract

In this study, nanoparticles with a monoclinic crystal structure of Gd_0.85−yLa_yPO₄:15%Eu were synthesized through a hydrothermal method. Initial investigations focused on the influence of the precursor on the resulting structure of LaPO₄:1%Eu, with variations in [...] Read more.

In this study, nanoparticles with a monoclinic crystal structure of Gd_0.85−yLa_yPO₄:15%Eu were synthesized through a hydrothermal method. Initial investigations focused on the influence of the precursor on the resulting structure of LaPO₄:1%Eu, with variations in synthesis temperature. Various syntheses were conducted using ammonium dihydrogen phosphate (NH₄H₂PO₄) and diammonium hydrogen phosphate ((NH₄)₂HPO₄) as PO₄³⁻ ion precursors, and the synthesis temperature ranged from room temperature to 200 °C. Based on the synthesis and analysis outcomes, diammonium hydrogen phosphate was selected as the precursor for PO₄³⁻ ions. Subsequent hydrothermal synthesis was performed at 180 °C to produce nanoparticles with a monoclinic crystal structure. After evaluating the synthesis and analysis results, the decision was made to increase the Eu³⁺ content from 1% to 15% by replacing La or Gd when a single-phase La_0.75Gd_0.24PO₄:1%Eu with a monoclinic crystal structure was achieved. These structural modifications were carried out in order to stabilize the anhydrous monoclinic structure and improve the luminescence properties of the phosphate. The synthesized samples were characterized using X-ray diffraction and scanning electron microscopy. Luminescence properties were meticulously measured and discussed. The emission intensity of monoclinic structure La_0.75Gd_0.1PO₄:15%Eu was found to be almost twice as high as compared with La_0.61Gd_0.24PO₄:15%Eu. Additionally, magnetization dependence on the applied magnetic field strength was measured, revealing paramagnetic properties in the investigated samples. Full article

(This article belongs to the Special Issue Advances in Functional Inorganic Materials Prepared by Wet Chemical Methods (Third Edition))

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12 pages, 2166 KiB

Open AccessArticle

¹¹⁹Sn Element-Specific Phonon Density of States of BaSnO₃

by Alexey Rulev, Hongxin Wang, Selma Erat, Murat Aycibin, Daniel Rentsch, Vladimir Pomjakushin, Stephen P. Cramer, Qianli Chen, Nobumoto Nagasawa, Yoshitaka Yoda and Artur Braun

Crystals 2025, 15(5), 440; https://doi.org/10.3390/cryst15050440 - 5 May 2025

Viewed by 102

Abstract

Vibration spectroscopy is routinely used in analytical chemistry for molecular speciation. Less common is its use in studying the dynamics of reaction and transport processes. A shortcoming of vibration spectroscopies is that they are not inherently specific to chemical elements. Progress in synchrotron [...] Read more.

Vibration spectroscopy is routinely used in analytical chemistry for molecular speciation. Less common is its use in studying the dynamics of reaction and transport processes. A shortcoming of vibration spectroscopies is that they are not inherently specific to chemical elements. Progress in synchrotron radiation-based X-ray technology has developed nuclear resonance vibration spectroscopy (NRVS), which can be used to produce element-specific vibration spectra and partial vibrational density of states (PVDOS), provided the material under investigation contains a Mössbauer-active element. While the method has been recently used successfully for protein spectroscopy, fewer studies have been conducted for condensed matter. We have employed NRVS on the BaSnO₃ perovskite structure, which is a model compound for ceramic proton conductors in intermediate temperature fuel cells. Since we used ¹¹⁹Sn as a Mössbauer isotope, the derived experimental PVDOS is specific to the element Sn in BaSnO₃. We show how this phonon DOS is used as an experimental anchor for the interpretation of the DFT-calculated PVDOS of BaSnO₃. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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18 pages, 4989 KiB

Open AccessArticle

Effect of TiO₂ Content on the Corrosion and Thermal Resistance of Plasma-Sprayed Al₂O₃-TiO₂ Coatings

by Viktorija Grigaitienė, Liutauras Marcinauskas, Airingas Šuopys, Romualdas Kėželis and Egidijus Griškonis

Crystals 2025, 15(5), 439; https://doi.org/10.3390/cryst15050439 - 3 May 2025

Viewed by 215

Abstract

Modern industrial systems and biomass-fired furnaces require surface treatments that can withstand aggressive chemical, thermal, and corrosive environments. This study investigates the corrosion and thermal resistance of plasma-sprayed Al₂O₃-TiO₂ coatings produced using a DC air–hydrogen plasma spray process. [...] Read more.

Modern industrial systems and biomass-fired furnaces require surface treatments that can withstand aggressive chemical, thermal, and corrosive environments. This study investigates the corrosion and thermal resistance of plasma-sprayed Al₂O₃-TiO₂ coatings produced using a DC air–hydrogen plasma spray process. Coatings of compositions of Al₂O₃, Al₂O₃-3 wt.% TiO₂, Al₂O₃-13 wt.% TiO₂, and Al₂O₃-40 wt.% TiO₂ were deposited on steel substrates with a Ni/Cr bond layer by plasma spraying. The coatings were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) to evaluate their morphology, elemental composition, and crystalline phases. Electrochemical tests were performed in a naturally aerated 0.5 mol/L NaCl solution and cyclic thermal–chemical exposure tests (500 °C using 35% KCl) to assess their corrosion kinetics and thermal stability. The results indicate that pure Al₂O₃ and low TiO₂ (3 wt.%) coatings exhibit fine barrier properties, while coatings with a higher TiO₂ content develop additional phases (e.g., Ti₃O₅, Al₂TiO₅) that improve thermal resistance but reduce chemical durability. Full article

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19 pages, 4241 KiB

Open AccessArticle

London Dispersive and Polar Surface Properties of Styrene–Divinylbenzene Copolymer Modified by 5-Hydroxy-6-Methyluracil Using Inverse Gas Chromatography

by Tayssir Hamieh and Vladimir Yu Gus’kov

Crystals 2025, 15(5), 438; https://doi.org/10.3390/cryst15050438 - 3 May 2025

Viewed by 513

Abstract

The London dispersive and polar surface properties of solid materials are very important in many chemical processes, such as adsorption, coatings, catalysis, colloids, and mechanical engineering. One of the materials, a styrene–divinylbenzene copolymer modified with 5-hydroxy-6-methyluracil at different percentages, has not been deeply [...] Read more.

The London dispersive and polar surface properties of solid materials are very important in many chemical processes, such as adsorption, coatings, catalysis, colloids, and mechanical engineering. One of the materials, a styrene–divinylbenzene copolymer modified with 5-hydroxy-6-methyluracil at different percentages, has not been deeply characterized in the literature, and it isparticularly crucial to determine its London dispersive and polar properties. Recent research in the inverse gas chromatography (IGC) technique allowed a full determination of the surface properties of a styrene–divinylbenzene copolymer modified with 5-hydroxy-6-methyluracil by using well-known polar and non-polar organic solvents and varying the temperature. Applying the IGC technique at infinite dilution resulted in the retention volume of adsorbed molecules on styrene–divinylbenzene copolymer modified with 5-hydroxy-6-methyluracil at different percentages, using the Hamieh thermal model and our recent results on the separation of the two polar and dispersive contributions to the free energy of interaction. The surface properties of these materials, such as the surface free energy of adsorption, the polar acid and base surface energy, and the Lewis acid–base parameters, were obtained as a function of temperature and for different percentages of 5-hydroxy-6-methyluracil. The obtained results proved that the polar free energy of adsorption on styrene–divinylbenzene copolymer increased when the percentage of 5-hydroxy-6-methyluracil (HMU) increased. However, a decrease in the London dispersive surface energy of the copolymer was observed for higher percentages of 5-hydroxy-6-methyluracil. A Lewis amphoteric character was shown for the copolymer with the highest acidity, while the basicity linearly increased when the percentage of HMU increased. Full article

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10 pages, 4289 KiB

Open AccessArticle

Theoretical Investigation of Chromium Separation from Chromates Through Photon–Phonon Resonant Absorption

by Mingyan Xie, Haoxin Ren, Yuanda Huang, Peilin Li, Yining Li, Yawen Li, Yuqi Xia and Peng Zhang

Crystals 2025, 15(5), 437; https://doi.org/10.3390/cryst15050437 - 3 May 2025

Viewed by 194

Abstract

Chromium (Cr) is a vital metal utilized in materials physics, healthcare, and various other domains. In this study, we propose an eco-friendly method for separating Cr from potassium chromate (K₂CrO₄) based on photon–phonon resonance absorption theory. Using first-principles density [...] Read more.

Chromium (Cr) is a vital metal utilized in materials physics, healthcare, and various other domains. In this study, we propose an eco-friendly method for separating Cr from potassium chromate (K₂CrO₄) based on photon–phonon resonance absorption theory. Using first-principles density functional theory calculations, we obtained the Raman and infrared spectra of K₂CrO₄ and assigned the vibrational modes to the peaks observed in the experimental spectra. We confirmed that the strongest infrared absorption peak corresponds to the Cr-O bond stretching vibration theoretically located at 931 cm⁻¹. We propose employing a high-power terahertz laser at this resonant frequency for photothermal energy transfer. This approach is expected to enhance the efficiency of separating Cr from K₂CrO₄. Experimental investigations are expected in the future. Full article

(This article belongs to the Special Issue Laser–Material Interaction: Principles, Phenomena, and Applications)

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11 pages, 1970 KiB

Open AccessArticle

Electrochemical and Photoresponsive Behavior of MOF-Derived V₂O₃/C Cathodes for Zinc-Ion Batteries: ZIF-8 as a Nanoscale Reactor and Carbon Source

by Byoungnam Park

Crystals 2025, 15(5), 436; https://doi.org/10.3390/cryst15050436 - 3 May 2025

Viewed by 154

Abstract

In this study, a V₂O₃/carbon (V₂O₃/C) composite was synthesized using zeolitic imidazolate framework 8 (ZIF-8) as both a sacrificial template and in situ carbon source. The composite was prepared by mixing ZIF-8 with NH₄ [...] Read more.

In this study, a V₂O₃/carbon (V₂O₃/C) composite was synthesized using zeolitic imidazolate framework 8 (ZIF-8) as both a sacrificial template and in situ carbon source. The composite was prepared by mixing ZIF-8 with NH₄VO₃, followed by annealing at 800 °C, resulting in nanoscale V₂O₃ embedded in a nitrogen-doped porous carbon matrix. Fabricated into a thin-film cathode via alternating current electrophoretic deposition (AC-EPD), the composite exhibited mixed capacitive–diffusion-controlled charge storage behavior with favorable Zn²⁺ transport kinetics, as confirmed by a b-value analysis (b = 0.72) and diffusion coefficient measurements (D_Zn = 6.2 × 10⁻¹¹ cm²/s). Notably, the cathode displayed photoresponsive redox behavior under 450 nm illumination, enhancing the Zn-ion kinetics. These findings demonstrate the potential of MOF-derived V₂O₃/C composites for high-performance, photo-enhanced zinc-ion energy storage applications. Full article

(This article belongs to the Special Issue Exploring New Materials for the Transition to Sustainable Energy)

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16 pages, 886 KiB

Open AccessArticle

Microstructure Evolution and the Influence on Residual Stress in Metal Additive Manufacturing with Analytics

by Wei Huang, Hamid Garmestani and Steven Y. Liang

Crystals 2025, 15(5), 435; https://doi.org/10.3390/cryst15050435 - 2 May 2025

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Abstract

Additive Manufacturing (AM) has become a revolutionary technology in manufacturing, attracting considerable attention in industrial applications recently. It allows for intricate fabrication, reduces material waste, offers design flexibility, and has economic implications. Nonetheless, the residual stresses generated during the AM process and their [...] Read more.

Additive Manufacturing (AM) has become a revolutionary technology in manufacturing, attracting considerable attention in industrial applications recently. It allows for intricate fabrication, reduces material waste, offers design flexibility, and has economic implications. Nonetheless, the residual stresses generated during the AM process and their effects on microstructural evolution and material properties continue to pose significant challenges hindering its advancement. This paper investigates the evolution of microstructures, focusing on texture and grain size as influenced by processing parameters. It examines how these factors affect the performance of multi-phase materials, specifically in terms of elastic modulus, Poisson’s ratio, and yield strength, leading to variations in residual stress through analytical simulation. The authors developed a thermal model that considers heat transfer boundaries and the geometry of the molten pool. They simulated grain size by considering the heating and cooling processes, including thermal stress, the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, and grain refinement. The texture was simulated using the Columnar-to-Equiaxed Transition (CET) model, thermal dynamics, and Bunge calculations. The self-consistency model determines the properties based on the established texture distribution. Finally, both microstructure-affected and non-affected residual stresses were modeled and compared. Two gaps between microstructure-affected residual stress and non-affected analytical models appear at the depths of 0.02 mm and 0.078 mm. The results indicate that controlling process parameters and optimizing microstructures can effectively reduce residual stresses, significantly enhancing the overall performance of AM components. Hence, this work provides a more accurate analytical residual stress model and lays the foundation for better control of residual stress in the AM industry. Full article

(This article belongs to the Special Issue Recent Advances in Additive Manufacturing of Metallic Materials: Characterization, Properties, and Modeling)

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18 pages, 12953 KiB

Open AccessArticle

Microstructural Investigation and High-Temperature Oxidation Performance of K417G Alloy Prepared by Wide-Gap Brazing

by Zhun Cheng, Xin Lai, Jing He, Xiaoqiang Li, Jiafeng Fan and Fuqiang Lai

Crystals 2025, 15(5), 434; https://doi.org/10.3390/cryst15050434 (registering DOI) - 2 May 2025

Viewed by 189

Abstract

K417G superalloy is widely applied in gas turbine components such as blades, vanes, and nozzles. In this work, the oxidation behavior and mechanism of K417G alloy prepared by wide-gap brazing were investigated in air at 800, 900, 1000, and 1100 °C. Microstructures of [...] Read more.

K417G superalloy is widely applied in gas turbine components such as blades, vanes, and nozzles. In this work, the oxidation behavior and mechanism of K417G alloy prepared by wide-gap brazing were investigated in air at 800, 900, 1000, and 1100 °C. Microstructures of the bonded joints differ in the wide-gap braze region (WGBR) and base metal (BM). The surface and cross-sectional morphology, composition, and structure of specimens were analyzed by XRD, SEM, and EDS after oxidation tests. The experimental data demonstrate that the WGBR‌ (wide-gap brazed region) exhibits markedly superior oxidation resistance compared to the BM‌ (base material) under elevated-temperature conditions exceeding 1000 °C. This performance disparity is quantitatively validated by oxidation kinetics analysis, where the weight gain curve of the WGBR demonstrates parabolic oxidation kinetics, as evidenced by its significantly lower parabolic rate constant relative to the BM. The oxide layers of the BM and WGBR are similar after oxidation at high temperatures of 800–900 °C, and they consist of an outermost layer of NiO, a middle mixed layer of Cr₂O₃, and an innermost layer of dendritic Al₂O₃. However, when the temperature is between 1000 and 1100 °C, the NiO on the surface of the BM falls off due to thermal expansion coefficient mismatch in coarse-grained regions, resulting in oxidation mainly divided into outer layer Cr₂O₃ and inner layer Al₂O₃ and TiO₂. Under high-temperature oxidation conditions (1000–1100 °C), a structural transition occurs in the oxide scale of the BM‌, with the underlying mechanism attributable to grain-coarsening-induced oxide scale destabilization‌. Specifically, the coarse-grained structure of the BM (characteristic grain size exceeding 50 μm) is exhibited. Therefore, the WGBR demonstrates outstanding oxidation resistance, as evidenced by the formation of a continuous Al₂O₃ scale with parabolic rate constants of about 1.38 × 10⁻³ mg²·cm⁻⁴·min⁻¹ at 1100 °C. Full article

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

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9 pages, 1803 KiB

Open AccessArticle

Inelastic Electron Tunneling Spectroscopy of Aryl Alkane Molecular Junction Devices with Graphene Electrodes

by Hyunwook Song

Crystals 2025, 15(5), 433; https://doi.org/10.3390/cryst15050433 - 1 May 2025

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Abstract

We present a comprehensive vibrational spectroscopic analysis of vertical molecular junction devices constructed using single-layer graphene electrodes separated by an aryl alkane monolayer. In this work, inelastic electron tunneling spectroscopy (IETS) is employed to probe molecular vibrations within the junction, providing an in [...] Read more.

We present a comprehensive vibrational spectroscopic analysis of vertical molecular junction devices constructed using single-layer graphene electrodes separated by an aryl alkane monolayer. In this work, inelastic electron tunneling spectroscopy (IETS) is employed to probe molecular vibrations within the junction, providing an in situ fingerprint of the molecules. Graphene has emerged as a promising electrode material for molecular electronics due to its atomically thin, mechanically robust nature and ability to form stable contacts. However, prior to this study, the vibrational spectra of molecules in graphene-based molecular junctions had not been fully explored. Here, we demonstrate that vertically stacked graphene electrodes can be used to form stable and reproducible molecular junctions that yield well-resolved IETS signatures. The observed IETS spectra exhibit distinct peaks corresponding to the vibrational modes of the sandwiched aryl alkane molecules, and all major features are assigned through density functional theory calculations of molecular vibrational modes. Furthermore, by analyzing the broadening of IETS peaks with temperature and AC modulation amplitude, we extract intrinsic vibrational linewidths, confirming that the spectral features originate from the molecular junction itself rather than extrinsic noise or instrumental artifacts. These findings conclusively verify the presence of the molecular layer between graphene electrodes as the charge transport pathway and highlight the potential of graphene–molecule–graphene junctions for fundamental studies in molecular electronics. Full article

(This article belongs to the Special Issue Advances in Multifunctional Materials and Structures)

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27 pages, 11438 KiB

Open AccessReview

Advances in Activation of Persulfate by Novel Carbon-Based Materials: Degradation of Emerging Contaminants, Mechanisms, and Perspectives

by Lianghui Guo, Dong Liu, Runyao Han, Aoxiang Yin, Guifan Gong, Shi Li, Ruixuan Chen, Jianyu Yang, Zimeng Liu and Keke Zhi

Crystals 2025, 15(5), 432; https://doi.org/10.3390/cryst15050432 - 1 May 2025

Viewed by 330

Abstract

Global industrialization has intensified the emission of emerging contaminants (ECs), posing a serious threat to the environment and human health. Persulfate-based advanced oxidation processes (PS-AOPs) have become a research hotspot due to their efficient degradation capability and environmentally friendly features; carbon-based materials are [...] Read more.

Global industrialization has intensified the emission of emerging contaminants (ECs), posing a serious threat to the environment and human health. Persulfate-based advanced oxidation processes (PS-AOPs) have become a research hotspot due to their efficient degradation capability and environmentally friendly features; carbon-based materials are ideal catalysts for activating persulfate (PS) due to their tunable electronic structure, abundant active sites, and low cost. This study summarizes the application of carbon-based materials (graphene, single-atom catalysts (SACs), etc.) in PS-AOPs, and provides insights into the degradation mechanisms of radicals (e.g., sulfate radical (SO₄^−·), hydroxyl radical (·OH)) and non-radicals (e.g., ¹O₂(singlet oxygen), electron transfer). The removal efficacy of carbon-based catalysts for antibiotics, phenols, and dyes was compared, and the key degradation pathways were elucidated. In addition, the activation of PS can be accelerated, and catalytic efficiency can be improved by synergizing with ancillary technologies (e.g., light, electricity). Despite the great potential of carbon-based catalysts, their large-scale application is limited by the complexity of the catalyst preparation process and the lack of selectivity for complex water qualities. Future studies can accelerate the practical application of PS-AOPs in wastewater treatment through the precise design of SACs and the construction of multi-mechanism synergistic activation systems. Full article

(This article belongs to the Special Issue Synthesis and Catalytic Performance of Transition Metal Catalysts)

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16 pages, 17834 KiB

Open AccessArticle

Study on Thermal Deformation Behavior and Thermal Processing Map of a New Al-Li Alloy

by Daoqi Chen, Xinyang Han, Yinggan Zhang, Yan Liu and Junfeng Chen

Crystals 2025, 15(5), 431; https://doi.org/10.3390/cryst15050431 - 30 Apr 2025

Viewed by 164

Abstract

As a representative third-generation Al-Li alloy, 2A97 alloy has attracted significant attention for applications in aeronautics and astronautics, but its poor hot workability and complex thermal deformation behavior, which make for difficult optimization, significantly limit its widespread industrial utilization. In this study, the [...] Read more.

As a representative third-generation Al-Li alloy, 2A97 alloy has attracted significant attention for applications in aeronautics and astronautics, but its poor hot workability and complex thermal deformation behavior, which make for difficult optimization, significantly limit its widespread industrial utilization. In this study, the thermal deformation behavior of 2A97 Al-Li alloy was systematically investigated via thermal compression tests conducted over a temperature range of 260–460 °C and strain rates ranging from 0.001 s⁻¹ to 1 s⁻¹. The effects of deformation parameters on the alloy’s microstructural evolution were examined using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Based on the dynamic materials model, a constitutive equation was established by analyzing the stress–strain data under various thermal deformation conditions. Furthermore, a thermal processing map was compiled to analyze the effects of the temperature and strain rate on the power dissipation efficiency and flow instability factor. The thermal deformation mechanisms were identified through combined analysis of the thermal processing map and microstructural features. Results indicate that the fraction of low-angle grain boundaries increases with a rising lnZ value (Zener–Hollomon parameter) during the thermal compression process. Dynamic recrystallization is the main deformation mechanism of 2A97 Al-Li alloy in the stable region, whereas the alloy exhibits flow localization in the unstable region. According to the thermal processing map, the optimal hot working windows for the 2A97 Al-Li alloy were determined to be (1) 360–460 °C at strain rates of 0.05 s⁻¹–1 s⁻¹, and (2) 340–420 °C at strain rates of 0.001 s⁻¹–0.005 s⁻¹. These conditions offer favorable combinations of microstructure and deformation stability, providing critical guidance for the thermo-mechanical processing of 2A97 alloy. Full article

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

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23 pages, 31507 KiB

Open AccessArticle

Tremolite-Asbestos Presence in Roman Archaeological Site of Micia, Romania

by Rodica-Mariana Ion, Marius Gheorghe Barbu, Valentin Ioan Gurgu, Sofia Slamnoiu-Teodorescu, Anca Irina Gheboianu, Gabriel Vasilievici, Lorena Iancu, Ramona Marina Grigorescu and Elvira Alexandrescu

Crystals 2025, 15(5), 430; https://doi.org/10.3390/cryst15050430 - 30 Apr 2025

Viewed by 155

Abstract

This paper reports the first evidence of the presence of the mineral tremolite asbestos in Roman building materials from the Micia archaeological site (Romania), thus contributing to the understanding of the implications of ancient building materials. The Micia archaeological site includes both a [...] Read more.

This paper reports the first evidence of the presence of the mineral tremolite asbestos in Roman building materials from the Micia archaeological site (Romania), thus contributing to the understanding of the implications of ancient building materials. The Micia archaeological site includes both a fort and a civilian Roman military settlement that was inhabited by both civilians and soldiers from various Roman troops. Over time, since the late 2nd century AD, the settlement has undergone significant reconstruction, especially after some fires. Tremolite asbestos is a non-flammable mineral that, due to its fibrous properties, was used in the past in building materials, although it poses health risks when inhaled. To highlight it, several advanced and highly sensitive scientific techniques are used in this work to discover the presence of tremolite asbestos and to examine its structure, composition, and morphology inside the investigated samples. Tremolite asbestos is typically white to gray or greenish in color, characterized by thin, needle-like fibers that can easily become airborne and inhaled. It is a crystalline mineral that usually forms long, straight, sharp fibers. Under high magnification in optical microscopy or in scanning electron microscope images, correlated with other performant analytical techniques (XRD, WDXRF, FTIR, Raman, BET, TGA), tremolite asbestos appears as elongated, slender fibers—often bundled or intertwined—with smooth or slightly striated surfaces. Full article

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

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21 pages, 13462 KiB

Open AccessArticle

Anisotropy in the Creep–Fatigue Behaviors of a Directionally Solidified Ni-Based Superalloy: Damage Mechanisms and Life Assessment

by Anping Long, Xiaoshan Liu, Lei Xiao, Gaoxiang Zhang, Jiangying Xiong, Ganjiang Feng, Jianzheng Guo and Rutie Liu

Crystals 2025, 15(5), 429; https://doi.org/10.3390/cryst15050429 - 30 Apr 2025

Viewed by 157

Abstract

Aero-engine turbine vanes made from directionally solidified nickel-based superalloys often fail with crack formation from the external wall of cooling channels. Therefore, this study simulates the compressive load on the external wall of the vane and conducts a sequence of creep–fatigue evaluations at [...] Read more.

Aero-engine turbine vanes made from directionally solidified nickel-based superalloys often fail with crack formation from the external wall of cooling channels. Therefore, this study simulates the compressive load on the external wall of the vane and conducts a sequence of creep–fatigue evaluations at 980 °C to investigate the creep–fatigue damage mechanisms of a directionally solidified superalloy and to assess its life. It is found that at low strain ranges, creep damage is dominant, with creep cavities forming inside the specimen and fatigue sources mostly distributed in the specimen interior. As the strain range increases, the damage mechanism transitions from creep-dominated to creep–fatigue coupled damage, with cracks nucleating preferentially on the surface and exhibiting a characteristic of multiple fatigue sources. In the longitudinal (L) specimen, dislocations in multiple orientations of the {111}<110> slip system are activated simultaneously, interacting within the γ channels to form dislocation networks, and dislocations shear through the γ′ phase via antiphase boundary (APB) pairs. In the transverse (T) specimen, stacking intrinsic stacking faults (SISFs) accumulate within the limited {111}<112> slip systems, subsequently forming a dislocation slip band. The modified creep–fatigue life prediction model, incorporating strain energy dissipation and stress relaxation mechanisms, demonstrates an accurate fatigue life prediction under creep–fatigue coupling, with a prediction accuracy within an error band of 1.86 times. Full article

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17 pages, 20014 KiB

Open AccessArticle

Molecular Dynamics Study of Nanoscratching Behavior of Water-Film-Covered GaN (0001) Surface Using Spherical Diamond Abrasive

by Jiaqin Yin, Shuaicheng Feng, Yang Liu and Jian Guo

Crystals 2025, 15(5), 428; https://doi.org/10.3390/cryst15050428 - 30 Apr 2025

Viewed by 148

Abstract

Molecular dynamics (MD) simulation of nanoscratching with a spherical diamond abrasive was performed to investigate the role of water molecular film on the surface nanotribological characteristics and subsurface lattice damage of GaN (0001) at the atomic level. The simulation results indicate that the [...] Read more.

Molecular dynamics (MD) simulation of nanoscratching with a spherical diamond abrasive was performed to investigate the role of water molecular film on the surface nanotribological characteristics and subsurface lattice damage of GaN (0001) at the atomic level. The simulation results indicate that the tangential and normal forces exhibited no significant variation trend with the increase in water film thickness. Inducing a water film can alleviate the material pile-up during scratching, and the GaN surface obtained the lowest friction coefficient and wear volume when the water film thickness reached 3 nm, primarily due to the enhanced lubrication and the heat absorption by the water film in this case. Water-film-covered GaN exhibited a thinner subsurface damage layer than the bare GaN, and the damage layer thickness decreased with the increase in water film thickness for various scratching depths of 1 to 4 nm. For each scratching depth, there was an optimal water film thickness causing the minimum number of amorphization atoms. Nevertheless, the water film failed to inhibit the formation and propagation of dislocations in the scratching process, and water-film-covered GaN exhibited more dislocations than the bare one. This research has the potential to expand the comprehension of water-mediated nanotribology and the ultra-precision machining procedures of GaN. Full article

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19 pages, 9508 KiB

Open AccessArticle

Preparation, Microstructure, and Properties of Solar Energy-Absorbing and -Storing Integrated Forsterite-Based Ceramics

by Xiaohong Xu, Yuntian Li, Tiantian Cheng, Jianfeng Wu, Yaqiang Shen, Saixi Qiu and Jiaqi Yu

Crystals 2025, 15(5), 427; https://doi.org/10.3390/cryst15050427 - 30 Apr 2025

Viewed by 172

Abstract

Solar energy-absorbing and -storing integrated ceramics are a new type of material that absorbs sunlight and stores it as heat energy, with properties such as high absorptivity, high thermal storage density, and high temperature stability. In this study, forsterite ceramics were prepared from [...] Read more.

Solar energy-absorbing and -storing integrated ceramics are a new type of material that absorbs sunlight and stores it as heat energy, with properties such as high absorptivity, high thermal storage density, and high temperature stability. In this study, forsterite ceramics were prepared from fused magnesia, quartz, α-Al₂O₃, and Sm₂O₃, and concurrently, two additives of Fe₂O₃ and CuO were doped to improve the absorptivity, and the effects of the composite additives on the performance of forsterite ceramics were investigated. The results showed that the optimal Fe₂O₃/CuO content ratio was 8:2, at which time the apparent porosity, bulk density, and thermal storage density of the sample were 0.21%, 3.08 g/cm³, and 1516.71 kJ/kg (1000 °C), respectively. After 30 thermal shock cycles, the precipitation of samarium silicate in the samples resulted in a tighter grain bonding, increased the bending strength by 70.6%, and exhibited excellent thermal shock resistance. The solar absorptivity reached 93.80% in the 0.3–2.5 μm wavelength range. Fe₂O₃ doping replaced part of the positions of Al³⁺ in MgAl₂O₄ to form MgFe_0.6Al_1.4O₄ phase. This replacement caused lattice distortion, which triggered electronic transition and augmented the intrinsic absorption capacity, thereby enhancing the sample’s absorptivity. CuO’s low reflectivity across the spectrum further reduced sample reflectivity. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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16 pages, 13986 KiB

Open AccessArticle

Orientation-Dependent Nanomechanical Behavior of Pentaerythritol Tetranitrate as Probed by Multiple Nanoindentation Tip Geometries

by Morgan C. Chamberlain, Alexandra C. Burch, Milovan Zečević, Virginia W. Manner, Marc J. Cawkwell and David F. Bahr

Crystals 2025, 15(5), 426; https://doi.org/10.3390/cryst15050426 - 30 Apr 2025

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Abstract

Nanoindentation can be leveraged to aid in the high fidelity modeling of dislocation mediated plasticity in pentaerythritol tetranitrate (PETN), an anisotropic energetic molecular crystal. Moreover, nanoindentation tip parameters such as tip geometry, size, and degree of acuity can be utilized to target anisotropic [...] Read more.

Nanoindentation can be leveraged to aid in the high fidelity modeling of dislocation mediated plasticity in pentaerythritol tetranitrate (PETN), an anisotropic energetic molecular crystal. Moreover, nanoindentation tip parameters such as tip geometry, size, and degree of acuity can be utilized to target anisotropic behavior. In this work, nanoindentation was conducted across a range of orientations on the (110) face of PETN to characterize resultant yield behavior, mechanical property measurements, and resultant slip behavior and fracture initiation. Three different indentation tips were utilized: a 3-sided pyramidal Berkovich tip, a 4-sided high aspect ratio Knoop tip, and a 90° conical tip. Ultimately, indenter tip radius was documented to impact yield behavior, whereas tip geometry affected larger scale processes such as slip, and tip acuity was the dominating factor that led to fracture. The axisymmetric conical tip, serving as a baseline, showed the least amount of variation in mechanical property measurements but also the largest distribution of maximum shear stress at which initial yielding occurred. Its high degree of acuity, however, was more prone to induce fracture at higher loads. The Knoop tip was shown to be suitable for average measurements, but also for elucidation of certain anisotropic features. A distinctly higher perceived hardness at 45° was measured with the Knoop tip, indicating less dislocation motion in that direction also observed in this work via scanning probe microscopy. Lastly, the commonly used Berkovich tip was a good compromise whereby it provided a representative volume element describing the average behavior of the material. These results can be utilized to target desired anisotropic behavior in a wider range of molecular crystals, as well as to inform theoretical considerations for dislocation mediated plasticity in PETN. Full article

(This article belongs to the Special Issue Microstructure and Characterization of Crystalline Materials)

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17 pages, 8251 KiB

Open AccessArticle

The Electrochemical Characteristics and Corrosion Resistance of a Low-Melting-Point Al49Sn21Zn16Pb14 Alloy in NaCl Solution

by Xiaofei Yao, Weihua Wang, Xiaoling Qi, Yunkun Lv, Wei Yang, Yufei Ma and Jian Chen

Crystals 2025, 15(5), 425; https://doi.org/10.3390/cryst15050425 - 30 Apr 2025

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Abstract

In this study, we prepared an innovative corrosion-resistant and low-melting-point Al49Sn21Zn16Pb14 alloy, and its microstructure was characterized. The corrosion resistance of the Al49Sn21Zn16Pb14 alloy in a NaCl solution with different concentrations was tested via electrochemical and immersion methods. In addition, the corrosion morphologies [...] Read more.

In this study, we prepared an innovative corrosion-resistant and low-melting-point Al49Sn21Zn16Pb14 alloy, and its microstructure was characterized. The corrosion resistance of the Al49Sn21Zn16Pb14 alloy in a NaCl solution with different concentrations was tested via electrochemical and immersion methods. In addition, the corrosion morphologies and products were analyzed via scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD), and the effects of the NaCl solution’s concentration on the corrosion resistance of the Al49Sn21Zn16Pb14 alloy were studied. The results showed that the melting point of the Al49Sn21Zn16Pb14 alloy was only 356.8 °C, and the melting temperature range was 356.8–377.6 °C. The microstructure of the Al49Sn21Zn16Pb14 alloy was dendritic, eutectic, and peritectic, and it had a face-centered cube (FCC) composition in the solid solution phase. The dendrite structure comprised an Al-rich solid solution primarily in the interdendrites and a Zn-rich solid solution mostly in the dendrites; the eutectic structure mainly consisted of Sn- and Pb-rich solid solutions; and the peritectic structure mainly comprised Zn- and Sn-rich solid solutions. In NaCl solutions of different concentrations, the Al49Sn21Zn16Pb14 alloy is generally corrosive; the corrosion rate of the Al49Sn21Zn16Pb14 alloy in 3.5% NaCl solution was 1.97 × 10⁻² mm/a; and the corrosion surface was loose or cracking. The corrosion products attached to the corrosion surface of the alloys mainly comprised Al and Zn oxides, while Sn and Pb corroded to form Sn and Pb oxides, which dissolved or fell off to form microholes or pores on the corrosion surface of the Al49Sn21Zn16Pb14 alloy. With an increase in the NaCl solution’s concentration, the degree of corrosion products that fell off or dissolved increased, and thus, the Al49Sn21Zn16Pb14 alloy’s corrosion rate increased. In 10.5% and 14% NaCl solutions, the amount of Al oxides in the corrosion products increased, and the locally dense corrosion product that formed on the corrosion surface of the Al49Sn21Zn16Pb14 alloy cracked and could not protect the matrix. The locally dense corrosion products on the surface of the Al49Sn21Zn16Pb14 alloy in NaCl solutions therefore could not improve the corrosion resistance. Full article

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18 pages, 29402 KiB

Open AccessArticle

Relationship Between Structure and Functional Properties of Ultrafine-Grained Fe-Mn-Si Alloys for Temporary Implants

by Olga Rybalchenko, Natalia Martynenko, Natalia Anisimova, Georgy Rybalchenko, Natalia Tabachkova, Elena Lukyanova, Igor Shchetinin, Diana Temralieva, Alexey Tokar, Petr Straumal, Pavel Dolzhenko, Andrey Belyakov, Mikhail Kiselevskiy and Sergey Dobatkin

Crystals 2025, 15(5), 424; https://doi.org/10.3390/cryst15050424 - 30 Apr 2025

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Abstract

This paper presents a study of microstructure formation in bioresorbable Fe-Mn-Si alloys for temporary implants under high-pressure torsion (HPT) at room temperature and at 300 °C. The effect of silicon on the mechanism of microstructure formation under HPT and, as a consequence, on [...] Read more.

This paper presents a study of microstructure formation in bioresorbable Fe-Mn-Si alloys for temporary implants under high-pressure torsion (HPT) at room temperature and at 300 °C. The effect of silicon on the mechanism of microstructure formation under HPT and, as a consequence, on the mechanical, corrosion and biological properties of the alloys is studied. It is established that Si promotes martensitic transformation. HPT leads to an increase in the microhardness values of the studied alloys from ~1560 MPa in the initial state to ~5500 MPa (160–560 HV) due to structure refinement and phase transformation. An increase in the electrochemical corrosion rate of Fe-Mn-Si alloys to ~0.5 mm/year is established due to grain refinement to nanosize and the formation of strain-induced martensite. In vitro cytotoxicity and induced hemolysis studies showed that Fe-Mn, Fe-Mn-3.7Si, and Fe-Mn-5Si alloys after annealing and HPT can be characterized as biocompatible. Full article

(This article belongs to the Special Issue Crystal Plasticity (4th Edition))

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12 pages, 1608 KiB

Open AccessArticle

Sm³⁺-Doped Bismuth(III) Oxosilicate (Bi₄Si₃O₁₂:Sm³⁺): A Study of Crystal Structure and Mulliken Charges

by Yan Zhang, Xuefeng Xiao, Yan Huang, Jiashun Si, Shuaijie Liang, Qingyan Xu, Huan Zhang, Lingling Ma, Cui Yang, Tianyong Ma, Xuefeng Zhang, Jiayue Xu, Tian Tian and Hui Shen

Crystals 2025, 15(5), 423; https://doi.org/10.3390/cryst15050423 - 30 Apr 2025

Viewed by 127

Abstract

In this paper, using the Materials Studio software (version 2020) and based on first-principles and density functional theory, the effects of Sm³⁺ doping at different ratios (1/12, 1/6, and 1/3) on the crystal structure and Mulliken charge distribution of bismuth silicate (Bi [...] Read more.

In this paper, using the Materials Studio software (version 2020) and based on first-principles and density functional theory, the effects of Sm³⁺ doping at different ratios (1/12, 1/6, and 1/3) on the crystal structure and Mulliken charge distribution of bismuth silicate (Bi₄Si₃O₁₂, BSO) were analyzed. The examination of the crystal framework and Mulliken charge allocation reveals that increasing levels of Sm³⁺ doping have the potential to warp the lattice’s symmetry and result in a decrease in electrical conductivity. With the rise in the concentration of Sm³⁺ doping, the Sm-O bond length shows a pattern of a rise at first and then a fall, demonstrating that electrons are shared, and reaches its minimum length with a doping proportion of 1/12. At the same time, when the doping concentration of Sm³⁺ rises, the Bi-O bond length becomes longer; it reaches its shortest length when the doping concentration is 1/12. This finding suggests that when a small quantity of Sm³⁺ is doped, especially when the doping concentration is 1/12, the covalent nature of the bonds between Sm-O and Bi-O atoms within the BSO crystal is strengthened. Full article

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