Crystals

18 pages, 3677 KB

Open AccessArticle

Synthesis of Cu_1.95Se Nanocrystals and Their Application in Photoacoustic Imaging

by Samuel Fuentes, Brady Killham, Juan Ramirez, Aditi Mulgaonkar, Rainie Luo, Yunfeng Wang, Jiechao Jiang, Robert Carson Sibley, Xiankai Sun and Yaowu Hao

Crystals 2026, 16(7), 476; https://doi.org/10.3390/cryst16070476 - 22 Jul 2026

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Abstract

Copper-deficient copper selenide (Cu_2−xSe) nanocrystals possess strong near-infrared (NIR) absorption and efficient photothermal conversion, making them attractive candidates for photoacoustic imaging. In this study, Cu_2−xSe nanocrystals with distinct morphologies were synthesized using different selenium precursors and evaluated as photoacoustic [...] Read more.

Copper-deficient copper selenide (Cu_2−xSe) nanocrystals possess strong near-infrared (NIR) absorption and efficient photothermal conversion, making them attractive candidates for photoacoustic imaging. In this study, Cu_2−xSe nanocrystals with distinct morphologies were synthesized using different selenium precursors and evaluated as photoacoustic contrast agents. Se–oleylamine precursors produced predominantly disk-shaped nanocrystals with average dimensions of approximately 20 nm in diameter and 5 nm in thickness, while Se–TOP/TOPO precursors yielded smaller spherical nanocrystals. Structural characterization by transmission electron microscopy, high-resolution TEM, and selected-area electron diffraction confirmed the formation of highly crystalline copper-deficient Cu_2−xSe nanocrystals with a face-centered cubic crystal structure. UV–Vis–NIR spectroscopy revealed broad optical absorption extending into the NIR region, with morphology-dependent spectral characteristics. Multispectral optoacoustic tomography demonstrated strong photoacoustic signal generation from both nanodisks and nanospheres over a broad wavelength range. In vivo studies using PEGylated Cu_2−xSe nanospheres showed successful lymphatic uptake following hind paw injection and enabled visualization of the draining popliteal lymph node through spectral unmixing of nanoparticle and hemoglobin signals. These results demonstrate that Cu_2−xSe nanocrystals are promising photoacoustic contrast agents for lymphatic imaging and other biomedical imaging applications. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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28 pages, 9258 KB

Open AccessArticle

The Blue Coloration of Natural Sapphires After Heating in Oxidizing and Reducing Environments

by Chunenapa Klomranok, Somruedee Sakkaravej, Wiwat Wongkokua, Chatree Saiyasombat and Natthapong Monarumit

Crystals 2026, 16(7), 475; https://doi.org/10.3390/cryst16070475 - 22 Jul 2026

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Abstract

The blue color of sapphire is associated with Fe and Ti impurities that replace Al³⁺ in the corundum structure. Typically, sapphire color depends on its geological origin, such as basaltic or metamorphic localities, and the blue hue can change after heating in [...] Read more.

The blue color of sapphire is associated with Fe and Ti impurities that replace Al³⁺ in the corundum structure. Typically, sapphire color depends on its geological origin, such as basaltic or metamorphic localities, and the blue hue can change after heating in an oxidizing environment. Nonetheless, previous studies on the blue color mechanism have left some questions unanswered. Therefore, this research examines how the oxidation states of Fe and Ti influence sapphire color and explores the mechanism of blue coloration before and after heating in oxidizing and reducing atmospheres. This study involved collecting sapphire samples from various gem localities, including basalt-related sapphires from Kanchanaburi, Thailand, and metamorphic-related sapphires from Sri Lanka. The samples were heated in an oxidizing environment at 1100 °C, then at either 1300 °C or 1500 °C in both oxidizing and reducing environments. As a result, after heating under an oxidizing environment at either 1300 °C or 1500 °C, the basalt-related sapphires turned from light blue to pale blue, and the metamorphic-related ones turned colorless. The Fe³⁺-Ti⁴⁺ mixed acceptor states decreased because an electron from the valence band recombined with a hole in the color center during heating. On the other hand, the blue color observed in sapphire samples after heating in a reducing environment at 1300 °C could be explained by electrons being depleted from the hole color center associated with Fe³⁺-Ti⁴⁺ mixed acceptor states within the energy band gap, thereby making them ready to receive electrons from the valence band upon optical excitation. Therefore, it can be concluded that the blue color mechanism in sapphires before and after heating under different atmospheric environments can be explained by an energy-band model involving the presence or absence of Fe³⁺-Ti⁴⁺ mixed acceptor states, as well as a hole color center within the energy band gap. Furthermore, after heating at 1300 °C and 1500 °C in a reducing environment, the oxidation state of Fe gradually decreases from 3+ to 2+. The samples turn black upon heating to 1500 °C, indicating that Fe²⁺-Ti⁴⁺ is responsible for the black color rather than the blue observed in sapphires. Full article

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

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11 pages, 4079 KB

Open AccessArticle

Judd–Ofelt Analysis and Laser Optical Properties of Nd³⁺-Doped S-FAP Nanocrystals as Precursors for Transparent Laser Ceramics

by Ke Yang, Guangyan Guo, Chen Li, Qianglong Chen, Yonghuan Wang and Ke Wang

Crystals 2026, 16(7), 474; https://doi.org/10.3390/cryst16070474 - 22 Jul 2026

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Abstract

Nd:S-FAP (Nd³⁺-doped Sr₅(PO₄)₃F) is a high-performance laser material recognized for its large stimulated emission cross-section and broad absorption bands, which are highly desirable for achieving efficient optical gain at the nanoscale. In this work, 5% [...] Read more.

Nd:S-FAP (Nd³⁺-doped Sr₅(PO₄)₃F) is a high-performance laser material recognized for its large stimulated emission cross-section and broad absorption bands, which are highly desirable for achieving efficient optical gain at the nanoscale. In this work, 5% Nd-doped Nd:S-FAP nanocrystals with an average grain size of approximately 9.2 nm were successfully synthesized via an improved hot-injection method. The results show that the fluorescence lifetime of the nanocrystals is 66 μs (166.56 μs for the ceramic), the quantum yield is 19.7% (69.6% for the ceramic), and the stimulated emission cross-section is 2.29 × 10⁻²⁰ cm² (5.74 × 10⁻²⁰ cm² for the ceramic). These discrepancies are primarily governed by surface-to-volume ratio variation-related surface effects, lattice distortions, and the weakening of non-radiative f–f transition processes due to quantum confinement at the nanoscale. This study reports for the first time the laser optical parameters of Nd:S-FAP nanocrystals, providing an experimental basis for the optimization of precursors for transparent laser ceramics and holding significant importance for the design of laser materials. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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17 pages, 14768 KB

Open AccessArticle

Fluence- and Layer-Dependent Defect Formation in CVD-Grown Graphene Under Low-Energy Nitrogen Ion Implantation

by Kyriakos Filintoglou, Nikolaos Pliatsikas, Panos Patsalas, Carsten Ronning, John Parthenios, Sotirios Ves, Konstantinos Papagelis, Dimitrios Christofilos and John Arvanitidis

Crystals 2026, 16(7), 473; https://doi.org/10.3390/cryst16070473 - 22 Jul 2026

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Abstract

Graphene grown by chemical vapor deposition (CVD) on polycrystalline Cu/Si and transferred onto SiO₂/Si substrates was subjected to low-energy nitrogen ion implantation (350 eV) at fluences ranging from 10¹² to 10¹⁶ cm⁻² and subsequently investigated by Raman spectroscopy [...] Read more.

Graphene grown by chemical vapor deposition (CVD) on polycrystalline Cu/Si and transferred onto SiO₂/Si substrates was subjected to low-energy nitrogen ion implantation (350 eV) at fluences ranging from 10¹² to 10¹⁶ cm⁻² and subsequently investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. Extensive Raman mapping performed prior to implantation indicates that the transferred samples consist predominantly of single-layer graphene (SLG), along with small domains of folded graphene (FG) that resemble bilayer graphene (BLG) with effectively random twist angles. At relatively low fluences, nitrogen ion implantation does not induce significant structural modifications in SLG, but leads to only a slight increase in doping compared to unimplanted samples. In contrast, at high ion fluences, SLG undergoes amorphization accompanied by severe damage of the substrate, as evidenced by the presence of an intense photoluminescence signal attributed to implantation-induced defects in the SiO₂ layer. Data analysis indicates that, for fluences 10¹³ and 10¹⁴, the implantation-induced defects in SLG are predominantly vacancy-like, with a smaller contribution from sp³-type defects, whereas FG domains appear less sensitive to defect accumulation. Full article

(This article belongs to the Special Issue Graphene-Based Nanocomposites)

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14 pages, 2821 KB

Open AccessArticle

Spin-Selective Up-Conversion Ho³⁺ Luminescence by Fe³⁺ Doping in Cs₂NaScCl₆:Ho³⁺ Crystals and Its Highly Sensitive X-Ray Detection Performance

by Hongyu Wu, Weiguo Huang, Yunlong Bai, Qingyi Huang, Yuewei Shi and Bingsuo Zou

Crystals 2026, 16(7), 472; https://doi.org/10.3390/cryst16070472 - 21 Jul 2026

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Abstract

This study investigated the effect of magnetic coupling of Fe³⁺ on Ho³⁺ luminescence in the double perovskite Cs₂NaScCl₆. Under 980 nm laser excitation, red emission from Ho³⁺ ions was observed in Cs₂NaScCl₆:Ho [...] Read more.

This study investigated the effect of magnetic coupling of Fe³⁺ on Ho³⁺ luminescence in the double perovskite Cs₂NaScCl₆. Under 980 nm laser excitation, red emission from Ho³⁺ ions was observed in Cs₂NaScCl₆:Ho³⁺/Fe³⁺ samples. We propose that this arises from spin-selective up-conversion mediated by magnetic polarons (EMPs). However, green emission from the ⁵F₄/⁵S₂ levels was not observed in this system. The experimental results suggest that localized EMPs form via ferromagnetic short-range ordering between Fe³⁺ and Ho³⁺ or among Fe³⁺ ions. These EMPs can be directly excited to higher energy levels via a biexciton absorption transition, then relaxed to the ⁵F₅ level of Ho³⁺ through ferromagnetic coupling. Under X-ray excitation, the characteristic emission peaks of Ho³⁺ in Cs₂NaScCl₆:Ho³⁺/Fe³⁺ become smoother, lose fine structure, and significantly decrease in intensity with increasing Fe³⁺ concentration. Based on this, we prepared Fe³⁺-free Cs₂NaScCl₆:Ho³⁺ and explored its excellent scintillation performance, with a detection limit as low as 37.73 nGy_air s⁻¹, below the medical diagnostic dose, surpassing the performance of commercial scintillators such as LuAG:Ce and BGO. This work reports the phenomenon of using Fe³⁺ as a sensitizer to achieve up-conversion sensitization in chloride double perovskites and demonstrates the application potential of Fe-free systems in ultra-low-dose X-ray imaging. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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20 pages, 28923 KB

Open AccessArticle

Effect of Aging Treatment on the Corrosion Behavior of Selective Laser Melted Fe-30Mn-8Al-1.5C-2.5Ni Lightweight Steel

by Fufei Deng, Hui Yang and Changling Zhuang

Crystals 2026, 16(7), 471; https://doi.org/10.3390/cryst16070471 - 21 Jul 2026

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Abstract

Selective laser melting (SLM) can effectively suppress metallurgical defects inherent to conventional manufacturing; however, subsequent aging treatments essential for engineering applications introduce secondary precipitates that alter the electrochemical homogeneity of the matrix. The underlying mechanism by which such precipitation behavior governs corrosion resistance [...] Read more.

Selective laser melting (SLM) can effectively suppress metallurgical defects inherent to conventional manufacturing; however, subsequent aging treatments essential for engineering applications introduce secondary precipitates that alter the electrochemical homogeneity of the matrix. The underlying mechanism by which such precipitation behavior governs corrosion resistance remains elusive. In this study, a Fe-30Mn-8Al-1.5C-2.5Ni steel was investigated to elucidate the corrosion morphology and electrochemical behavior of the as-built, 450 °C-aged, and 750 °C-aged specimens during immersion in a 3.5 wt.% NaCl solution. The results demonstrate that the inherent Mn microsegregation and high-density subgrain boundaries induced by SLM trigger preferential localized anodic dissolution on the surface of the as-built sample, culminating in the formation of a loose, porous manganese oxide product layer. Aging treatment at 450 °C induces extensive precipitation of κ-carbides within grain interiors and along grain boundaries, accompanied by localized depletion of Al and Mn at the phase interfaces. A pronounced micro-galvanic coupling established between the κ-carbides and the adjacent Al-depleted zones directly compromises the continuity of the passive film, thereby further deteriorating the corrosion resistance. In contrast, aging at 750 °C relieves the residual stress and eliminates the as-built elemental microsegregation. The resulting compositional homogenization of the matrix reduces the localized electrochemical driving force, which promotes a uniform reaction of Al at the surface to construct a continuous, compact Al-rich passive film, thereby sustaining the highest charge-transfer resistance during long-term immersion. This work elucidates the correlation among the intrinsic defects of SLM, aging-induced solute-depleted zones, κ-carbide precipitation, and localized micro-galvanic corrosion, providing a fundamental basis for tailoring the microstructure and corrosion resistance of additively manufactured lightweight steels. Full article

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

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16 pages, 5882 KB

Open AccessArticle

Effect of Increasing Fe₂O₃ Content on the Structural, Thermal, and Optical Characteristics of Soda–Lime–Silica Glass-Ceramics

by Raluca A. Mereu, Alexandru Turza, Oana Raita and Mioara Zagrai

Crystals 2026, 16(7), 470; https://doi.org/10.3390/cryst16070470 - 21 Jul 2026

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Abstract

In this study, a series of xFe₂O₃–Na₂O–CaO–SiO₂ glass-ceramics containing 0–28 wt.% Fe₂O₃ were prepared via the conventional melt-quenching technique. The resulting samples, designated S1–S4, were subsequently subjected to thermal treatment and investigated with [...] Read more.

In this study, a series of xFe₂O₃–Na₂O–CaO–SiO₂ glass-ceramics containing 0–28 wt.% Fe₂O₃ were prepared via the conventional melt-quenching technique. The resulting samples, designated S1–S4, were subsequently subjected to thermal treatment and investigated with respect to their structural, thermal, and optical characteristics. Differential scanning calorimetry analysis revealed the influence of the Fe₂O₃ concentration on the glass transition temperature and crystallization behavior of the samples. Structural analysis of the samples revealed that crystalline silicate and iron oxide phases constituted the predominant crystalline phases, with their overall crystallinity being strongly dependent on the Fe₂O₃ content and thermal treatment. Fourier transform infrared spectroscopy evidenced structural modifications of the silicate network induced by iron incorporation, while ultraviolet–visible–near infrared spectroscopy highlighted the presence of Fe²⁺/Fe³⁺ ions and their associated electronic transitions. The results indicate that increasing the Fe₂O₃ content significantly affects the network structure, redox state, and thermal behavior of the glass-ceramic system, leading to enhanced absorption properties. Full article

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

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17 pages, 12385 KB

Open AccessArticle

Research on the Development Method and Adsorptive Characteristics of Lightweight and High-Strength Ceramsite Produced from Coal Gangue

by Yao Wang, Zhenfei Lv, Han Yu, Xuejia Zhang, Yukun Cao, Xiulin Shen, Junchi Weng, Shenglong Xie, Yanghui Ke and Biao Hu

Crystals 2026, 16(7), 469; https://doi.org/10.3390/cryst16070469 - 21 Jul 2026

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Abstract

The prolonged outdoor storage of coal gangue leads to significant environmental issues, while the contamination of water by antibiotics poses a worldwide health concern. Conventional adsorbents are often hindered by their expense and fragility. Current studies on ceramsite derived from coal gangue have [...] Read more.

The prolonged outdoor storage of coal gangue leads to significant environmental issues, while the contamination of water by antibiotics poses a worldwide health concern. Conventional adsorbents are often hindered by their expense and fragility. Current studies on ceramsite derived from coal gangue have not successfully combined the repurposing of solid waste with the management of water pollution. This research utilized coal gangue and waste electric porcelain as primary materials, incorporating 2 wt.% calcium carbonate as a foaming agent, and produced ceramsite through a gradient-heating sintering process. The investigation thoroughly examined how sintering temperature and particle size distribution influenced the material’s performance. Findings indicated that mullite-based ceramsite, sintered at 1400 °C for 15 min, achieved an apparent porosity of 35.68% and a compressive strength of 10.03 MPa. A particle size distribution following a normal model resulted in a 7.9% removal efficiency of 20.00 mg/L tetracycline hydrochloride in just 30 min, with a minimal post-adsorption strength decrease of 3.7%. This study offers a theoretical framework and practical guidance for the effective utilization of coal gangue and the economical treatment of antibiotic-laden wastewater. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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24 pages, 62418 KB

Open AccessArticle

Improving the Microstructural and Mechanical Properties of Agricultural Ploughs Through Atmospheric Plasma Spray (APS) Thermal Coatings

by Fabian Cezar Lupu, Corneliu Munteanu, Bogdan Istrate, Gelu Ianus, Grigore Marian, Nazar Boris, Teodor Marian, Marcelin Benchea and Vlad Nicolae Arsenoaia

Crystals 2026, 16(7), 468; https://doi.org/10.3390/cryst16070468 - 21 Jul 2026

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Abstract

This paper presents experimental investigations carried out on components belonging to agricultural plough assemblies, which undergo significant mechanical loading during soil tillage operations. Due to severe operating conditions, ploughs are subjected to abrasive wear and impact stresses, so that enhancing these properties translates [...] Read more.

This paper presents experimental investigations carried out on components belonging to agricultural plough assemblies, which undergo significant mechanical loading during soil tillage operations. Due to severe operating conditions, ploughs are subjected to abrasive wear and impact stresses, so that enhancing these properties translates into improved performance, accompanied by a lower failure rate and, consequently, reduced downtime in agricultural activity. In order to upgrade the material properties of the active parts that come into direct and sustained contact with the soil—and which are therefore most vulnerable to degradation—surface thermal coatings were applied by means of Atmospheric Plasma Spray (APS) deposition, with the aim of extending service performance and component lifespan. The mechanical properties of the deposited coatings were assessed through hardness testing (approx. 204 HV) and microscratch behaviour evaluation (COF > 1). In addition, microstructural examinations were conducted using scanning electron microscopy to characterise the surface condition following the thermal deposition process. The findings confirm that thermal coatings represent a viable technical solution, enabling not only the improvement of plough component properties, but also the possibility of reconditioning worn parts by compensating, through thermal deposition, for the material loss caused by soil-induced wear during field operation. Full article

(This article belongs to the Special Issue Thermal Coatings: Properties and Applications)

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17 pages, 50150 KB

Open AccessArticle

Effects of Substrate Polarity and Pre-Growth Treatments on Plasma-Assisted Molecular-Beam Epitaxy of β-Ga₂O₃ on 4° Off-Axis 4H-SiC

by Raouf Hayyak, Trong Si Ngo, Taswar Iqbal, Mee-Hi Choi, Soon-Ku Hong, Im-Gyu Yeo, Moonkyong Na and Tai Hee Eun

Crystals 2026, 16(7), 467; https://doi.org/10.3390/cryst16070467 - 21 Jul 2026

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Abstract

This study reports the growth and structural analysis of β-Ga₂O₃ films on 4° off-axis (000±1) Si- and C-face 4H-SiC substrates by plasma-assisted molecular-beam epitaxy (PAMBE). Pre-growth treatments of 4H-SiC substrates were conducted by employing: (I) unintentional oxygen exposure, (II) intentional [...] Read more.

This study reports the growth and structural analysis of β-Ga₂O₃ films on 4° off-axis (000±1) Si- and C-face 4H-SiC substrates by plasma-assisted molecular-beam epitaxy (PAMBE). Pre-growth treatments of 4H-SiC substrates were conducted by employing: (I) unintentional oxygen exposure, (II) intentional Ga pre-exposure, (III) a Ga flash-off process followed by Ga pre-exposure, and (IV) intentional oxygen-plasma pre-exposure prior to β-Ga₂O₃ growth, which led to different growth behaviors. The intentional Ga pre-exposure and Ga flash-off followed by Ga pre-exposure treatments modified the initial Si-face surface condition and were consistent with the mitigation of oxygen-induced surface degradation, including possible SiO_x-related effects. In contrast, unintentional oxygen exposure and intentional oxygen-plasma pre-exposure produced RHEED evolution consistent with substantial surface disordering and possible amorphous SiO_x formation on the Si-face 4H-SiC substrate, leading to disordered nucleation and degraded film growth. Growth on the C-face 4H-SiC substrate resulted in more ordered β-Ga₂O₃ films, suggesting that the C-face surface is less susceptible to SiO_x-related degradation under the present oxygen-containing growth environment. The combined in situ RHEED, AFM, and HRXRD results indicate that substrate polarity and pre-growth surface treatments strongly influence the initial nucleation, morphology, and crystalline quality of β-Ga₂O₃ films on 4H-SiC. These findings provide a useful strategy for controlling oxide film growth on easily oxidized substrates under oxygen environments. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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9 pages, 308 KB

Open AccessArticle

Electrostatic–Elastic Softening and Ultraviolet Instability Driven by Non-DLVO Interactions in Charged Colloidal Crystals

by Hao Wu and Zhong-Can Ou-Yang

Crystals 2026, 16(7), 466; https://doi.org/10.3390/cryst16070466 - 20 Jul 2026

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Abstract

Colloidal crystals permeated by mobile ions exhibit a coupling between electrostatic and elastic degrees of freedom that renormalizes the effective screening length and induces wave-vector-dependent elastic softening. Building on our recently proposed continuum model, we perform a rigorous Gaussian fluctuation analysis to elucidate [...] Read more.

Colloidal crystals permeated by mobile ions exhibit a coupling between electrostatic and elastic degrees of freedom that renormalizes the effective screening length and induces wave-vector-dependent elastic softening. Building on our recently proposed continuum model, we perform a rigorous Gaussian fluctuation analysis to elucidate the stability limits of the homogeneous phase. By integrating out the electrostatic fluctuations, we derive the effective elastic modulus

Γ (q)

as a function of wave vector q. We show that the modulus in the long-wavelength limit (

q \to 0

) remains identically equal to a bare modulus protected by perfect ionic screening. In contrast, the modulus in the short-wavelength limit (

q \to \infty

) softens as the electrostatic-elastic coupling strength

ξ

increases, vanishing at a critical value

ξ = 1

. For

ξ > 1

, the fluctuation spectrum exhibits a negative eigenvalue for all wave vectors q larger than a critical (effective screening) wave vector

q_{c}

, signaling an ultraviolet instability of the uniform phase. In a real colloidal crystal, this divergence is regulated by the discrete lattice cutoff

q_{\max} \sim π / a

, confining the physical instability to a finite band

q_{c} < q < q_{\max}

. The macroscopic limit

q \to 0

remains unconditionally stable for all

ξ

. The transition at

ξ = 1

thus marks the onset of short-wavelength mechanical failure, while macroscopic elastic stiffness remains intact. Our analysis clarifies the proper physical interpretation of the minimal coupling model and provides a consistent picture of how non-DLVO interactions can drive local structural collapse in charged colloidal crystals. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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16 pages, 2853 KB

Open AccessArticle

Chiral Behavior and Racemization of Salen-Type Ligands and Their Iron Complexes: An X-Ray Crystal Structure Study

by Marika Iwatani, Daisuke Nakane and Takashiro Akitsu

Crystals 2026, 16(7), 465; https://doi.org/10.3390/cryst16070465 - 18 Jul 2026

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Abstract

Chiral salen-type metal complexes are promising for diverse applications, yet their crystals often exhibit complicated chiral behavior. We investigated the crystal structures of chlorine-substituted salen-type ligands incorporating a 1,2-diphenylethylenediamine moiety and their iron complexes, which revealed varied chiral phenomena. Synthesis of the ligands [...] Read more.

Chiral salen-type metal complexes are promising for diverse applications, yet their crystals often exhibit complicated chiral behavior. We investigated the crystal structures of chlorine-substituted salen-type ligands incorporating a 1,2-diphenylethylenediamine moiety and their iron complexes, which revealed varied chiral phenomena. Synthesis of the ligands using (1S,2S)-, (1R,2R)-, and racemic starting amines exclusively produced racemic ligands. A similar racemization of the ligand was observed during the formation of a dinuclear oxidized Fe(III)-O-Fe(III) complex from FeSO₄·6H₂O (1). Conversely, complexation with FeCl₃ maintained the optically active (1S,2S)-configuration even in the iron(III) complex (2). To elucidate these structural features, intermolecular interactions were quantified via Hirshfeld surface analysis. Additionally, generative AI (Gemini, Google) was employed for data interpretation to discuss the correlation between the structural characteristics of chirality and Hirshfeld surface analysis. Full article

(This article belongs to the Special Issue Synthesis, Crystal Structures and Hirshfeld Surface Analysis of Coordination Compounds (4th Edition))

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14 pages, 5344 KB

Open AccessArticle

A Phenomenological Model for Dynamic Expansion of Defects in Semiconductor Lasers

by Yuqi Zhang, Jia Zhao and Feng Gao

Crystals 2026, 16(7), 464; https://doi.org/10.3390/cryst16070464 - 17 Jul 2026

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Abstract

The failures of semiconductor lasers are often linked to the emergence or growth of defects. However, most research mainly focuses on the postmortem failure analysis caused by defects, lacking dynamic process analysis of defect expansion. This limitation hinders the understanding of defect growth [...] Read more.

The failures of semiconductor lasers are often linked to the emergence or growth of defects. However, most research mainly focuses on the postmortem failure analysis caused by defects, lacking dynamic process analysis of defect expansion. This limitation hinders the understanding of defect growth patterns and expansion. In this work, we establish a macroscopic phenomenological model based on the dynamic characteristics of defects in semiconductor lasers. The expansion of defects is regarded as the diffusion transfer process of lattice strain, and the diffusion-limited aggregation (DLA) model is used to describe the aggregation process of random morphology of defects. The effect of model parameters on the growth pattern is studied, and the phenomenological relation between model parameters and actual defect features is established. The model successfully replicated experimentally observed morphologies in a distributed feedback (DFB) laser under high-temperature and high-current excitation. It not only predicts the intermediate process of defect expansion but also reveals the accelerated process. This research provides a novel approach to describing the defect evolution process in semiconductor lasers, contributing to a deeper understanding of defect expansion modes and characteristics within semiconductor lasers. It holds significant guiding implications for improving device reliability. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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5 pages, 155 KB

Open AccessEditorial

Bridging Material Design and Intelligent Systems in Low-Dimensional Materials for Electronics and Sensing

by Hu Li and Klaus Leifer

Crystals 2026, 16(7), 463; https://doi.org/10.3390/cryst16070463 - 17 Jul 2026

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Abstract

Low-dimensional materials have become central to the development of emerging electronic, optoelectronic, sensing, energy-storage, and information-processing technologies [...] Full article

(This article belongs to the Special Issue Advances in Low-Dimensional Materials for Electronics and Sensing Applications)

15 pages, 14656 KB

Open AccessArticle

Microstructure and Wear Resistance of IN625-2NbC-2SiC Composite Coatings Prepared Under Different Laser Powers

by Kun Cheng, Zhengwei Cui, Tao Zhang and Kewang Yin

Crystals 2026, 16(7), 462; https://doi.org/10.3390/cryst16070462 - 17 Jul 2026

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Abstract

IN625-2NbC-2SiC composite coatings were successfully deposited on IN625 substrates using laser cladding technology. This study systematically explores the dependency of phase assemblage, microstructural characteristics, microhardness, and wear behavior on the applied laser power. Experimental results show that the phase composition of the coatings [...] Read more.

IN625-2NbC-2SiC composite coatings were successfully deposited on IN625 substrates using laser cladding technology. This study systematically explores the dependency of phase assemblage, microstructural characteristics, microhardness, and wear behavior on the applied laser power. Experimental results show that the phase composition of the coatings remains essentially unchanged across different power levels, primarily consisting of γ-(Ni, Cr), NbC, and SiC, with partial retention or reprecipitation of NbC particles. Under low laser power, local defects rich in Si and C appear in the coating, which is primarily attributed to insufficient melting or uneven dispersion of SiC particles. An optimal power of 1500 W results in a more homogeneous structure, better elemental distribution, and improved carbide dispersion. However, excessively high laser power may lead to excessive heat input, reduced cooling rate, and local microstructural inhomogeneity. Microhardness and tribological tests demonstrate that laser cladding significantly improves the surface properties of the IN625 substrate. The average microhardness values of the substrate, S1 to S4 are 250.5, 345.4, 357.2, 367.1, and 338.2 HV, respectively. Among them, the S3 coating exhibits the highest microhardness, which is approximately 46.5% higher than that of the substrate. Meanwhile, the S3 coating shows the lowest average friction coefficient and wear rate. The wear resistance ranking is as follows: S3 > S2 > S1 > S4 > substrate. The superior wear resistance of S3 is largely due to its high hardness, uniform structure, and well-distributed carbide reinforcements, which strengthen its resistance to deformation and abrasive wear. Based on overall consideration of phase, microstructure, and tribological performance, 1500 W is concluded to be the optimal laser power under the conditions investigated. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 3rd Edition)

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25 pages, 9044 KB

Open AccessArticle

Microstructural Evolution and ISO-Based Weld Quality in MAG and Laser Welding of HC420LA Steel Under Different Heat Inputs

by Cemil Kobak and Arzum Işıtan

Crystals 2026, 16(7), 461; https://doi.org/10.3390/cryst16070461 - 16 Jul 2026

Viewed by 441

Abstract

In this study, HC420LA steel plates joined by gas metal arc welding (MAG), manual laser welding (ML), and robotic laser welding (RL) were comparatively examined under heat input (HI) levels obtained from an active production line exhibiting weld defects. The effect of HI [...] Read more.

In this study, HC420LA steel plates joined by gas metal arc welding (MAG), manual laser welding (ML), and robotic laser welding (RL) were comparatively examined under heat input (HI) levels obtained from an active production line exhibiting weld defects. The effect of HI and welding method on mechanical properties, microstructural evolution, phase characteristics, and weld integrity was evaluated using tensile and hardness tests, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Weld imperfections were evaluated according to ISO 5817:2023(E) for MAG welds and BS EN ISO 13919-1:2019 for laser welds, and the corresponding quality levels were determined. The highest tensile strength (568 MPa) and elongation (23%) were achieved in RL welds at the lowest HI value (0.108 kJ/mm), with fracture occurring outside the weld region, indicating superior joint integrity and mechanical compatibility with the base metal. In contrast, MAG and ML welds exhibited a non-linear relationship between HI and ductility and tensile strength. ML welds showed higher hardness and reduced ductility due to the formation of harder transformation products, while MAG welds demonstrated a non-linear response associated with heat-affected zone (HAZ) coarsening. Heterogeneous phase distribution XRD analysis confirmed the presence of α-Fe-based phases and secondary alloyed structures, while EDS analyses revealed a relatively homogeneous distribution of the principal alloying elements within the weld regions and provided supporting evidence for the Mn₃O₄ oxide phase identified in the RL welds. SEM observations further demonstrated distinct microstructural transitions across the fusion zone (FZ) and HAZ, reflecting the influence of the welding process and heat input on weld evolution. The assessment of weld imperfections according to the relevant ISO standards showed that ML and RL welds satisfied Quality Level B, whereas MAG welds exhibited quality levels ranging from B to D, depending on the evaluated imperfection. These results indicate that equivalent HI values do not guarantee comparable weld quality or mechanical performance across different welding processes. The study provides insight into the relationship between heat input, weld quality, microstructural evolution, phase constitution, and mechanical performance in HSLA steels. Full article

(This article belongs to the Special Issue Advances in High-Performance Alloys)

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16 pages, 2356 KB

Open AccessArticle

Synergistic Modulation of Nonlinear Thomson Scattering Radiation in a Cross-Collision Geometry by Laser Amplitude and Initial Electron Energy

by Zihan Li, Yunyun Shi and Anlei Zhang

Crystals 2026, 16(7), 460; https://doi.org/10.3390/cryst16070460 - 15 Jul 2026

Cited by 1 | Viewed by 238

Abstract

Relativistic nonlinear Thomson scattering (RNTS) provides an effective route for generating ultrashort and high-frequency radiation. Its radiation characteristics are determined not only by the laser field strength, represented by the laser amplitude

a_{0}

(the normalized laser amplitude), but also by the initial [...] Read more.

Relativistic nonlinear Thomson scattering (RNTS) provides an effective route for generating ultrashort and high-frequency radiation. Its radiation characteristics are determined not only by the laser field strength, represented by the laser amplitude

a_{0}

(the normalized laser amplitude), but also by the initial electron energy, expressed by

γ_{0}

(the initial Lorentz factor). To further clarify the coupled effects of

a_{0}

and

γ_{0}

in a cross-collision geometry, this study employs a tightly focused circularly polarized Gaussian laser field model including high-order nonparaxial corrections, and investigates the variations in electron dynamics and radiation behavior under different laser amplitudes

a_{0}

and initial Lorentz factors

γ_{0}

. The numerical results show that increasing

a_{0}

enhances the nonlinear oscillation and instantaneous acceleration of the electron in the laser field, thereby increasing the radiation intensity and promoting spectral extension toward higher-frequency regions. In contrast, increasing

γ_{0}

strengthens the relativistic inertia of the electron, making its motion more directional and further affecting the angular distribution and temporal compression characteristics of the emitted radiation. The combined action of these two parameters leads to pronounced tunability in the spatial directivity, temporal structure, and spectral broadening of the radiation. These results help clarify the parameter-dependent mechanism of RNTS radiation under strong-field conditions and provide useful guidance for the optimization of high-brightness, highly collimated, broadband ultrafast radiation sources. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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10 pages, 2720 KB

Open AccessArticle

Microstructural Evolution and Phase Formation in Nanocrystalline Ti_0.8V_0.2C Powder During High-Energy Mechanical Alloying

by Mohsen Mhadhbi, Baris Avar, Abdulrahman Mallah and Mohamed Khitouni

Crystals 2026, 16(7), 459; https://doi.org/10.3390/cryst16070459 - 14 Jul 2026

Viewed by 264

Abstract

A nanostructured Ti_0.8V_0.2C solid solution carbide was successfully synthesized via high-energy mechanical alloying (MA) of elemental Ti, V, and C powders for 20 h in a planetary ball mill under argon atmosphere. Phase evolution and microstructural transformation were tracked [...] Read more.

A nanostructured Ti_0.8V_0.2C solid solution carbide was successfully synthesized via high-energy mechanical alloying (MA) of elemental Ti, V, and C powders for 20 h in a planetary ball mill under argon atmosphere. Phase evolution and microstructural transformation were tracked using XRD, SEM/EDX, and TEM. Progressive alloying resulted in continuous refinement of the carbide structure, where the crystallite size was reduced to ~11–15 nm and the lattice microstrain increased up to 0.93 % after 20 h of MA. TEM observations confirmed the formation of highly dispersed nanocrystalline Ti_0.8V_0.2C solid-solution carbide particles with sizes of 15–20 nm. This work demonstrates the effectiveness of MA in generating a novel Ti–V-based nanocarbide solid solution and highlights the critical role of milling duration in tailoring structural refinement and defect accumulation at the nanoscale. Full article

(This article belongs to the Topic Advanced Ceramics: Processing, Properties, and Applications)

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13 pages, 5271 KB

Open AccessArticle

Alkaline-Earth-Site Confinement Enables 98% Quantum Yield Orange Emission in Mn-Doped Cadmium Halide

by Dan Luo, Tao Huang, Shuaigang Ge, Yongqiang Zhao and Bingsuo Zou

Crystals 2026, 16(7), 458; https://doi.org/10.3390/cryst16070458 - 14 Jul 2026

Viewed by 309

Abstract

The luminescence efficiency of Mn²⁺-doped metal halides is often limited by concentration quenching caused by Mn-Mn interactions. In this work, the alkaline-earth cadmium chloride BaCd₂Cl₆·6H₂O:Mn²⁺ was synthesized via a mechanical grinding method. The three-dimensional [...] Read more.

The luminescence efficiency of Mn²⁺-doped metal halides is often limited by concentration quenching caused by Mn-Mn interactions. In this work, the alkaline-earth cadmium chloride BaCd₂Cl₆·6H₂O:Mn²⁺ was synthesized via a mechanical grinding method. The three-dimensional network framework of this compound effectively isolates Mn²⁺ ions with a Mn-Mn separation of 4.87 Å, thereby suppressing concentration quenching. Under 254 nm ultraviolet excitation, the sample exhibits efficient orange emission centered at 588 nm with a photoluminescence quantum yield (PLQY) as high as 98%. Temperature-dependent photoluminescence studies reveal that the optimal emission temperature of this system is 320 K, demonstrating good thermal stability. This work achieves, for the first time, near-unity Mn²⁺ luminescence efficiency in a Ba-site alkaline-earth cadmium halide system, demonstrating that alkaline-earth-site confinement provides an effective strategy for achieving highly efficient Mn-doped halide luminescence. Full article

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

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15 pages, 2341 KB

Open AccessArticle

Study on the Electromechanical Coupling Properties and Tuning Mechanisms of Ta-Doped Lithium Niobate Crystals Based on First-Principles Calculations

by Jiahao Li, Xuefeng Xiao, Han Zhang, Xu Han, Jiayi Chen, Yan Huang, Yan Zhang, Shuaijie Liang, Huan Zhang, Lingling Ma, Cui Yang, Jiandong Wu, Xuefeng Zhang and Yong Yang

Crystals 2026, 16(7), 457; https://doi.org/10.3390/cryst16070457 - 13 Jul 2026

Viewed by 294

Abstract

This study investigates the effects of Ta doping on the elastic, dielectric, piezoelectric, and electromechanical coupling properties of lithium niobate (LiNbO₃, LN) crystals using first-principles calculations. The results show that isovalent substitution of Nb⁵⁺ by Ta⁵⁺ maintains mechanical stability [...] Read more.

This study investigates the effects of Ta doping on the elastic, dielectric, piezoelectric, and electromechanical coupling properties of lithium niobate (LiNbO₃, LN) crystals using first-principles calculations. The results show that isovalent substitution of Nb⁵⁺ by Ta⁵⁺ maintains mechanical stability in all doped systems. Ta incorporation enhances the overall stiffness and deformation resistance, while strengthening ionic displacement polarization and the piezoelectric stress response. The piezoelectric strain constant d₃₃ and electromechanical coupling coefficient k₃₃ exhibit different optimal doping concentrations. d₃₃ reaches 9.548 pC/N at 10% Ta doping, corresponding to a 13.6% improvement over intrinsic LN, whereas k₃₃ reaches a maximum of 0.2569 at 3.33% Ta doping and remains high in the 3.33–6.67% range. This separation originates from the competition among polarization enhancement, elastic stiffness hardening, and nonlinear dielectric growth. Enhanced ionic polarization promotes d₃₃, while excessive dielectric energy storage and increased stiffness suppress effective electromechanical energy conversion. These results reveal the microscopic mechanism governing composition-dependent electromechanical tuning in Ta-doped LN crystals. Accordingly, 10% Ta is suitable for improving strain sensitivity, whereas 3.33–6.67% Ta is preferable for optimizing energy conversion efficiency in LN-based sensors, actuators, transducers, and resonators. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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19 pages, 23516 KB

Open AccessArticle

Influence of Phosphorus Incorporation on the Crystallization Behavior and Electrochemical Properties of Portland Cement

by Seunghyeon Kim, Miyoung You, BoRa Park, Hye-Rin Choi, Woosung Yum, Byung-Hyun Shin and Pungkeun Song

Crystals 2026, 16(7), 456; https://doi.org/10.3390/cryst16070456 - 13 Jul 2026

Viewed by 285

Abstract

The growing demand for sustainable construction materials has sparked interest in innovative cementitious components that improve performance while mitigating environmental impact. This study explores the influence of red phosphorus (P) on the crystallization dynamics and electrochemical stability of Portland cement. Specifically, we investigate [...] Read more.

The growing demand for sustainable construction materials has sparked interest in innovative cementitious components that improve performance while mitigating environmental impact. This study explores the influence of red phosphorus (P) on the crystallization dynamics and electrochemical stability of Portland cement. Specifically, we investigate how varying phosphorus concentrations (0–10%) affect phase evolution and structural integrity. A comprehensive suite of analytical techniques, including field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), was employed to characterize crystallization behavior. Additionally, open circuit potential (OCP), potentiodynamic polarization tests, and electrochemical impedance spectroscopy (EIS) were utilized to evaluate electrochemical properties. Quantitative defect analysis showed that the number of pores increased from 150 ± 22 to 420 ± 22 ea/mm², the crack width increased from 0.10 ± 0.01 to 1.40 ± 0.60 μm, and the crack length increased from 1.20 ± 0.20 to 4.20 ± 1.21 μm. In addition, OCP shifted from −0.16 ± 0.01 to −0.27 ± 0.03 V, I_corr increased from 2 × 10⁻⁷ ± 1 × 10⁻⁸ to 8 × 10⁻⁷ ± 3 × 10⁻⁸ A/cm², and R_p decreased from 10.5 ± 0.4 to 6.0 ± 0.2 kΩ with increasing P composition, indicating deterioration of the microstructural and electrochemical stability of the cement matrix. These findings provide quantitative guidance for controlling phosphorus utilization in cement formulations. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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16 pages, 4811 KB

Open AccessArticle

Effect of Nb Content on the Stability and Electronic Properties at bcc-Fe/NbN Interface

by Faye Li, Xiaoyang Luo, Jiawei Shen, Xuefeng Lu, Jie Sheng and Xingchang Tang

Crystals 2026, 16(7), 455; https://doi.org/10.3390/cryst16070455 - 13 Jul 2026

Viewed by 207

Abstract

First-principles calculations based on density functional theory were employed to systematically investigate the atomic structure, stability, and Nb segregation behavior of the bcc-Fe(100)/NbN(100) interface. Convergence tests of surface energy determined that an interface model consisting of 7 bcc-Fe layers and 5 NbN layers [...] Read more.

First-principles calculations based on density functional theory were employed to systematically investigate the atomic structure, stability, and Nb segregation behavior of the bcc-Fe(100)/NbN(100) interface. Convergence tests of surface energy determined that an interface model consisting of 7 bcc-Fe layers and 5 NbN layers is appropriate. The work of adhesion and interfacial energy were calculated for four interface configurations with different terminations. Interface 2 was identified as the most thermodynamically stable configuration, exhibiting a work of adhesion of 0.569 J/m² and an interfacial energy of 3.221 J/m². Nb atoms displayed pronounced site-selective segregation at the interface; the segregation tendency decreases in the order site 1 (−0.74 eV) > site 2 (−0.59 eV) > site 4 (−0.38 eV) > site 3 (−0.24 eV). Electronic structure analysis indicated that strong hybridization between Nb-4d and Fe-3d orbitals near the Fermi level leads to localized charge accumulation, which is the electronic origin of interfacial strengthening. As the Nb concentration increases from 1.6 at.% to 6.3 at.%, the segregation energy continuously drops from −0.74 eV to −1.55 eV, the work of adhesion monotonically increases from 0.569 J/m² to 0.786 J/m², and the interfacial energy decreases from 3.221 J/m² to 2.374 J/m², demonstrating that Nb segregation significantly enhances the interfacial stability. The calculation results provide a theoretical framework for understanding the experimentally observed evolution of Nb(C,N) precipitates and offer insights for the optimization of Nb microalloying in 442D ferritic stainless steel. Full article

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

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12 pages, 6982 KB

Open AccessArticle

Modeling and Simulation of an All-Optical 1 × 2 Decoder Based on a Two-Dimensional Photonic Crystal Ring Resonator

by Fariborz Parandin, Mahya Parnianchi and Saeed Olyaee

Crystals 2026, 16(7), 454; https://doi.org/10.3390/cryst16070454 - 13 Jul 2026

Viewed by 281

Abstract

In this paper, a simple and compact 1 × 2 decoder based on a two-dimensional photonic crystal structure is proposed, whose operation relies on total internal reflection and photonic band gaps. The designed structure employs a square-lattice configuration of silicon dielectric rods embedded [...] Read more.

In this paper, a simple and compact 1 × 2 decoder based on a two-dimensional photonic crystal structure is proposed, whose operation relies on total internal reflection and photonic band gaps. The designed structure employs a square-lattice configuration of silicon dielectric rods embedded in air. The decoder consists of two input ports, one acting as a Bias port and the other as a logical input port. Numerical modeling and simulations are performed using the plane-wave expansion (PWE) method and the finite-difference time-domain (FDTD) technique. The proposed coupling-resonator structure increases the coupling efficiency at resonant frequencies. The structure has a relatively small footprint, comprising an 18 × 18 array of dielectric rods with a total area of approximately 147 µm². A minimum contrast ratio of about 8.4 dB between logical “1” and “0” states is achieved. The decoder operates at 1.55 µm, making it suitable for photonic and optical communication applications. Due to its compact size, simple architecture, and use of a minimal number of ring resonators, the proposed decoder is well suited for high-speed photonic integrated circuits and future all-optical computing systems. The bit rate of the proposed decoder is estimated to be 2 Tb/s. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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11 pages, 1424 KB

Open AccessArticle

Laser-Driven Vortex Flow in a Nematic Droplet: Experimental and Numerical Results

by Dmitrii P. Shcherbinin, Semyon S. Rudyi, Denis A. Glukharev, Izabela Śliwa, Pavel V. Maslennikov and Alex V. Zakharov

Crystals 2026, 16(7), 453; https://doi.org/10.3390/cryst16070453 - 13 Jul 2026

Viewed by 250

Abstract

The dynamic evolution of an optically induced vortex flow in nematic microliter droplets caused by exposure to a focused laser beam has been studied both experimentally using polarized optical microscopy and numerically within the framework of a corresponding nonlinear extension of the Ericksen–Leslie [...] Read more.

The dynamic evolution of an optically induced vortex flow in nematic microliter droplets caused by exposure to a focused laser beam has been studied both experimentally using polarized optical microscopy and numerically within the framework of a corresponding nonlinear extension of the Ericksen–Leslie theory supplemented by thermomechanical correction of the stress tensor and the entropy balance equation. The vortex flow in nematic droplets consisting of 4-pentyl-4′-cyanobiphenyl molecules spreading over the functionalized surface was visualized in microliter droplets doped with monodisperse polystyrene tracers, under exposure to a laser beam with an optical power equal to 8.0 mW. Using the computer vision detection algorithm, we have identified radial symmetry in the tracers motion, where comet-like tracks are aligned along the rays emanating from the center of the resulting structure. At the same time, some of the “comets” are flying towards the center, while others are moving away from it. This allowed us to estimated the average value of tracer flows, which is of 17 µm/s. All these observations indicate that vortex currents are excited in the droplet under the action of the focused laser beam. The nature of thermally excited vortex flows in the microliter hybrid aligned nematic droplet with a free upper LC/air interface and spreading over the solid surface under the influence of the heat flux directed through the lower bounding surface is also numerically investigated. It was shown that due to the interaction between

\nabla T

and the gradient of the director field

\nabla \hat{n}

, the thermally driven bi-vortical flow is maintained in nematic microvolume. Full article

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

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12 pages, 19492 KB

Open AccessArticle

Solute Hydrogen Effects on the Uniaxial Tension Response of Polycrystalline α-Fe by Molecular Dynamics Simulation

by Jiawei Chen, Man Luo, Yameng Wang, Wen Yu, Zengqi Ji, Yongqiang Zhang, Xiaoqing Chen and Xiangsheng Hu

Crystals 2026, 16(7), 452; https://doi.org/10.3390/cryst16070452 - 13 Jul 2026

Viewed by 347

Abstract

The premature fracture failure of polycrystalline α-Fe poses lots of hidden safety problems due to hydrogen absorption during human activities. A key challenge for the failure process is understanding the effects of hydrogen on grain boundaries (GBs). The study here demonstrates that [...] Read more.

The premature fracture failure of polycrystalline α-Fe poses lots of hidden safety problems due to hydrogen absorption during human activities. A key challenge for the failure process is understanding the effects of hydrogen on grain boundaries (GBs). The study here demonstrates that the rapid diffusion of hydrogen leads to the formation of hydrogen-induced defects in a very short time. Specifically, hydrogen segregation results in void formation and even aggregation at GBs, which plays a critical role in crack initiation and propagation. The mechanical response of GBs with varying hydrogen levels is investigated using large-scale molecular dynamics (MD) simulations. The analysis shows that hydrogen increases the yield stress, thereby inhibiting dislocation emission from GBs. Additionally, GB damage alters the fracture mode from a mix of intergranular and intragranular fracture without hydrogen to a fully intergranular fracture with multi-site crack nucleation at high hydrogen concentrations (e.g., C_h = 3 at.%). This shift is driven by hydrogen-induced void formation at GBs and hydrogen’s rapid diffusion, which accelerates crack propagation along the grain boundaries. Full article

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

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21 pages, 19584 KB

Open AccessArticle

Balancing Microstructural Refinement and Electrochemical Homogeneity in ECAP-Processed Mg-Y-Zn Alloys via Mn/Zr Microalloying

by Lisha Wang, Wei Shen, Haoran Wu, Lulu Wang, Chenchen Zhang and Wenbin Tao

Crystals 2026, 16(7), 451; https://doi.org/10.3390/cryst16070451 - 12 Jul 2026

Viewed by 334

Abstract

This study reveals the synergistic effects of Mn and Zr microalloying and equal-channel angular pressing (ECAP) on the microstructure and corrosion behavior of Mg-Y-Zn alloys in Hanks’ solution. At moderate deformation levels (four passes), the alignment of LPSO phases forms semi-continuous barrier structures, [...] Read more.

This study reveals the synergistic effects of Mn and Zr microalloying and equal-channel angular pressing (ECAP) on the microstructure and corrosion behavior of Mg-Y-Zn alloys in Hanks’ solution. At moderate deformation levels (four passes), the alignment of LPSO phases forms semi-continuous barrier structures, promoting the formation of dense corrosion product layers and improving corrosion resistance. (e.g., Mg-Y-Zn-Mn 4p: 1.07 mm·y⁻¹). However, excessive deformation (eight passes) leads to severe fragmentation of LPSO phases, increasing cathodic activity and intensifying micro-galvanic coupling in Mn-containing alloys (Mg-Y-Zn-Mn 8p: 2.61 mm·y⁻¹). In contrast, Zr-containing alloys exhibit continuous improvement in corrosion resistance with increasing ECAP passes, attributed to enhanced electrochemical uniformity resulting from homogeneous ultrafine-grained structures (Mg-Y-Zn-Zr 8p: 0.87 mm·y⁻¹). These findings elucidate the critical mechanism by which the interplay between microalloying chemistry and severe plastic deformation governs electrochemical uniformity and corrosion kinetics. This work provides new insight into the corrosion behavior of ECAP-processed Mg-Y-Zn alloys, highlighting the critical role of balancing microstructural refinement and electrochemical heterogeneity, and offers guidance for the optimization of corrosion-resistant Mg-based materials. Full article

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24 pages, 37696 KB

Open AccessArticle

Valorization of Red Mud, Steel Slag, and Desulfurization Slag as Industrial Solid-Waste-Derived Catalysts for Ciprofloxacin Degradation via H₂O₂ and Peroxymonosulfate Activation

by Yan Lin, Jingyan Li, Jiayu Yang, Rui Xu, Dunqiu Wang, Kun Dong, Ruize Sun and Mingrong Wei

Crystals 2026, 16(7), 450; https://doi.org/10.3390/cryst16070450 - 11 Jul 2026

Viewed by 336

Abstract

This study used red mud (RM), steel slag (SS), and desulfurization slag (DS) as raw materials to construct three catalytic oxidation systems, namely RM-DCDA/H₂O₂, SS-DS/H₂O₂, and SS-DS/peroxymonosulfate (PMS), to promote the utilization of industrial solid [...] Read more.

This study used red mud (RM), steel slag (SS), and desulfurization slag (DS) as raw materials to construct three catalytic oxidation systems, namely RM-DCDA/H₂O₂, SS-DS/H₂O₂, and SS-DS/peroxymonosulfate (PMS), to promote the utilization of industrial solid waste and enhance the treatment of recalcitrant antibiotic wastewater. The ciprofloxacin (CIP) degradation performances, influencing factors, and preliminary reaction mechanisms of these systems were investigated. RM formed an Fe₃N/C composite structure after acidification and dicyandiamide-assisted calcination. The Fe₃N active phase, coexistence of Fe²⁺/Fe³⁺, and N-doped C structure facilitated H₂O₂ activation and electron transfer. The SS-DS catalyst exhibited a rough and porous structure and contained Fe, Ca, and S species, which could provide reactive sites for H₂O₂ and PMS activation, following acid modification and urea-assisted calcination. Under the necessary reaction conditions, the CIP degradation efficiencies of the RM-DCDA/H₂O₂, SS-DS/H₂O₂, and SS-DS/PMS systems reached 94.60%, 92.58%, and 95.17%, respectively. These results indicate that RM- and SS-derived materials can be used for CIP oxidative degradation; however, the values should not be interpreted as a strict comparison of the intrinsic catalytic activity because the operating conditions differed among the systems. Parametric experiments showed that the catalyst dosage, oxidant concentration, and initial pH influenced the degradation efficiency. The H₂O₂-based systems were more suitable under acidic conditions, whereas the SS-DS/PMS system showed wider pH adaptability. Coexisting anion and humic acid experiments indicated that the systems were tolerant to natural organic matter, whereas HCO₃⁻ and HPO₄²⁻ inhibited degradation. CIP was further oxidized in total organic C and recycling experiments; however, it was difficult to completely mineralize it within a short reaction time, and the catalyst retained relatively high activity after repeated use. Radical quenching experiments suggested that ·OH and ·O₂⁻ participated in the degradation reactions in the RM-DCDA/H₂O₂ and SS-DS/H₂O₂ systems. In the SS-DS/PMS system, comparative quenching experiments revealed that non-radical singlet oxygen (¹O₂) was the dominant reactive species, while SO₄⁻· and ·OH contributed only marginally. In conclusion, RM and SS-DS can be used as low-cost raw materials to prepare industrial solid-waste-derived catalysts for the oxidative degradation of CIP, thereby providing a reference for industrial solid waste valorization and antibiotic wastewater treatment. Full article

(This article belongs to the Special Issue Synergizing Crystallography, Mineral Materials Science and Solid Waste Upcycling for Sustainable Materials Innovation)

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17 pages, 3596 KB

Open AccessArticle

Superhydrophobic, Corrosion-Resistant ORMOSIL Coating on 6061 Aluminum Alloy for Aviation Fuel Environments

by Xiang Liu, Huijie Sun, Jiaxing Ru, Xiao Hu, Rui Lu, Yumo Wang, Lei Zhang and Hengcheng Wan

Crystals 2026, 16(7), 449; https://doi.org/10.3390/cryst16070449 - 10 Jul 2026

Viewed by 273

Abstract

During aviation operations, low temperatures can cause fuel freezing and icing on 6061 aluminum fuel lines, threatening flight safety. To mitigate this, a surface treatment combining FeCl₃ etching and an ORMOSIL sol–gel coating was proposed to construct a superhydrophobic functional layer. FeCl [...] Read more.

During aviation operations, low temperatures can cause fuel freezing and icing on 6061 aluminum fuel lines, threatening flight safety. To mitigate this, a surface treatment combining FeCl₃ etching and an ORMOSIL sol–gel coating was proposed to construct a superhydrophobic functional layer. FeCl₃ etching generated a hierarchical micro/nanostructure on the aluminum surface, while the ORMOSIL layer, formed by the co-hydrolysis and condensation of PFOTES and HDTMS, built Si-O-Si networks and introduced C-F groups to reduce surface energy and enhance stability. The modified surface showed a high water contact angle of 161.44°, confirming excellent superhydrophobicity. AFM analysis revealed a significant increase in surface roughness (Sa = 0.844 μm), confirming the formation of a hierarchical micro/nanostructure. Electrochemical measurements showed a positive shift in corrosion potential from −0.723 V to −0.652 V, demonstrating enhanced corrosion resistance. More importantly, after 120 h of immersion in aviation fuel, the coating maintained a high contact angle of 156.73° and preserved its Si-O-Si network and fluorinated functional groups, confirming outstanding fuel resistance and long-term stability. These results demonstrate that the proposed ORMOSIL coating is a promising protective strategy for aviation fuel systems operating under low-temperature and corrosive conditions. Full article

(This article belongs to the Special Issue Recent Progress in Corrosion Protection of Materials)

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25 pages, 13189 KB

Open AccessReview

Advances in Homoepitaxial Mosaic Single-Crystal Diamond: Interface Stress Regulation

by Rong Rong and Jie Bai

Crystals 2026, 16(7), 448; https://doi.org/10.3390/cryst16070448 - 10 Jul 2026

Viewed by 361

Abstract

Single-crystal diamond is regarded as one of the most promising semiconductor materials for next-generation high-power electronic devices, quantum technologies, and extreme environmental applications, owing to its ultra-wide bandgap, exceptionally high carrier mobility, ultra-high breakdown electric field, and excellent thermal conductivity. However, the lateral [...] Read more.

Single-crystal diamond is regarded as one of the most promising semiconductor materials for next-generation high-power electronic devices, quantum technologies, and extreme environmental applications, owing to its ultra-wide bandgap, exceptionally high carrier mobility, ultra-high breakdown electric field, and excellent thermal conductivity. However, the lateral dimensions of both natural and synthetic single-crystal diamond are limited, which severely restricts their large-scale industrial application. Mosaic growth, in which multiple small single-crystal seeds are laterally arranged and fused at the interfaces through homoepitaxial growth, offers a promising approach to overcoming the size limitation of seed crystals and producing inch-scale single-crystal wafers. This review systematically covers the entire mosaic growth process, including seed crystal preparation, geometric design, growth parameter optimization, and innovative processing methods. Particular emphasis is placed on the mechanisms of interfacial stress generation, along with characterization techniques and stress control strategies. Finally, future perspectives on the fabrication of large-size, low-stress single-crystal diamond wafers are outlined. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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19 pages, 30636 KB

Open AccessArticle

Development of a Flow-Stress Constitutive Model and Hot-Processing Window for a High-Nb, Ultra-High-Strength (205 ksi) Nickel-Based Corrosion-Resistant Alloy

by Dadi Zhou, Gang Meng, Wei Jiang, Tengzhong Zhang and Zhiqiang Wang

Crystals 2026, 16(7), 447; https://doi.org/10.3390/cryst16070447 - 10 Jul 2026

Viewed by 213

Abstract

The development of unconventional deep oil and gas resources requires 205 ksi high-Nb Ni-based corrosion-resistant alloys; however, the lack of hot-forming databases and processing maps for this grade has frequently resulted in hot cracking during ingot forging. To address this gap, this study [...] Read more.

The development of unconventional deep oil and gas resources requires 205 ksi high-Nb Ni-based corrosion-resistant alloys; however, the lack of hot-forming databases and processing maps for this grade has frequently resulted in hot cracking during ingot forging. To address this gap, this study investigated the hot-deformation behavior of this alloy and optimized its forming parameters. Isothermal-compression tests were performed using a Gleeble 3800-GTC simulator (Dynamic Systems Inc., Poestenkill, NY, USA) at 1173–1323 K and strain rates of 0.01–10 s⁻¹, followed by quantitative electron backscatter diffraction (EBSD) characterization of grain size, kernel average misorientation (KAM), and grain-boundary misorientation. A strain-compensated Arrhenius constitutive model was developed, giving a deformation activation energy of 540.33 kJ/mol and an average absolute relative error of only 4.77%. Dynamic materials model (DMM)-based power-dissipation and instability maps were constructed for this alloy for the first time, and an optimal hot-working window of 1260–1300 K and 0.01–0.1 s⁻¹ was identified. Under the representative condition of 1273 K and 0.1 s⁻¹, a uniform fine-grained microstructure with well-developed dynamic recrystallization was obtained without cracking, with an average grain size of 10.91 μm, a dynamic recrystallization (DRX) fraction of 48.4%, and an average KAM value of 0.476°. This work establishes the first complete hot-processing map system for the 205 ksi high-Nb Ni-based alloy, clarifies the coupled effects of dislocation evolution and dynamic recrystallization, and provides theoretical guidance for industrial hot cogging and microstructural control. Full article

(This article belongs to the Special Issue Investigation of Microstructural and Properties of Steels and Alloys)

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