Crystals

13 pages, 1110 KB

Open AccessArticle

by Kyrill Yu. Suponitsky, Ekaterina V. Bogdanova, Aleksei A. Anisimov and Igor B. Sivaev

Crystals 2026, 16(5), 350; https://doi.org/10.3390/cryst16050350 - 20 May 2026

The crystal molecular structure of the co-crystal of boric acid (BA) with triphenylphosphine oxide (TPO) 1:2, H₃BO₃∙2Ph₃PO, was determined by single-crystal X-ray diffraction. In the crystal, pairs of the boric acid molecules are connected to each other [...] Read more.

The crystal molecular structure of the co-crystal of boric acid (BA) with triphenylphosphine oxide (TPO) 1:2, H₃BO₃∙2Ph₃PO, was determined by single-crystal X-ray diffraction. In the crystal, pairs of the boric acid molecules are connected to each other by hydrogen bonds, and each acid molecule forms two hydrogen bonds with the oxygen atoms of two triphenylphosphine oxide molecules. The crystal packing of the new complex was compared with the crystal packings of the known 1:1 complex of boric acid and triphenylphosphine oxide, and boric acid and triphenylphosphine oxide themselves. Also, the energetic preferences and densities of the co-formers (BA and TPO) were compared for their pure forms and co-crystals. It is shown that more tight crystal packing is not necessarily accompanied by higher stability. Full article

(This article belongs to the Section Crystal Engineering)

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15 pages, 4103 KB

Open AccessArticle

Photocatalytic Activity of Cu–TiO₂ Nanopowder Under UVA and Sunlight Illumination: Influence of Composition and Calcination Temperature on Charge Transfer

by Khley Cheng, Sothanith Chourn, Vichheka So, Ford David, Solida Long, Sarah Dine, Alex Lemarchand, Mamadou Traore, Christophe Colbeau-Justin and Andrei Kanaev

Crystals 2026, 16(5), 349; https://doi.org/10.3390/cryst16050349 - 19 May 2026

Abstract

Cu–TiO₂ nanoparticles of a broad range of compositions with 0, 0.002, 0.005, 0.02, 0.05, 0.2, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0 and 10.0 mol% Cu were synthesized via the sol–gel method using copper (II) acetate and titanium tetraisopropoxide (TTIP) precursors at a [...] Read more.

Cu–TiO₂ nanoparticles of a broad range of compositions with 0, 0.002, 0.005, 0.02, 0.05, 0.2, 0.5, 1.0, 2.0, 3.0, 5.0, 7.0 and 10.0 mol% Cu were synthesized via the sol–gel method using copper (II) acetate and titanium tetraisopropoxide (TTIP) precursors at a low hydrolysis ratio of H = 1.25, which favours homogeneous TiO₂ nucleation and Cu dispersion in the host matrix at nanoscale. The precipitated materials were dried at 80 °C and calcined at 450, 500, and 550 °C to form crystalline nanopowders, whose photocatalytic activity was evaluated on the decomposition of a representative pollutant, methylene blue (MB), in aqueous solutions under UVA and sunlight illuminations. The compositions with small Cu content of ~0.05 mol% showed the highest activity. A gain of activity over pure titania of 4 times after calcination at 450 °C, 2.5 times at 500 °C and 20% at 550 °C was measured under UVA illumination. Even higher gain of activity observed under sunlight illumination might be due to an extension of action spectrum to the visible range due to intra-gap defect states produced by Cu²⁺ insertion. The time-resolved microwave conductivity (TRMC) measurements of the photoinduced charges relaxation suggest that both excessive calcination temperature and Cu content decrease the activity due to Cu-defects clustering. Modelling relates the activity to the photoinduced electron-hole pair separation; the optimal Cu content is explained by accessibility of the recombination centre by a conduction band (CB) electron. Accordingly, an increase in calcination temperature resulted in a longer pathlength of CB electron. Full article

(This article belongs to the Special Issue Research on Complex Oxide Nanomaterials)

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37 pages, 3231 KB

Open AccessReview

Impact of Advanced Ceramic-Based Structures on the Design and Technology of Receiving Antennas for Global Navigation Satellite System

by Romeo Cristian Ciobanu, Alina Ruxandra Caramitu, Magdalena Valentina Lungu, Ioana Ion, Mircea Popescu, Adrian Parfeni and Răducu Machidon

Crystals 2026, 16(5), 348; https://doi.org/10.3390/cryst16050348 - 19 May 2026

Abstract

This study emphasizes how the Global Navigation Satellite System (GNSS) receiving antenna technology transcends the boundaries of traditional ceramics manufacturing techniques, expanding their design options and improving the functional attributes of ceramic components for GPS, Galileo, GLONASS, and BeiDou applications. Ceramics exhibit exceptional [...] Read more.

This study emphasizes how the Global Navigation Satellite System (GNSS) receiving antenna technology transcends the boundaries of traditional ceramics manufacturing techniques, expanding their design options and improving the functional attributes of ceramic components for GPS, Galileo, GLONASS, and BeiDou applications. Ceramics exhibit exceptional material characteristics, such as excellent thermal resistance, outstanding electrical insulation, considerable hardness, and notable wear resistance, making them suitable for GNSS technology, due to their capacity to form intricate shapes and microstructures for applications in aerospace, electronics, and automotive sectors. The research systematically outlines the impact of advanced ceramic-based structures upon various antenna design, technology and types, relevant to their particular applications: antennas with alumina substrates, antennas that use FR4 substrate, antennas that use a PCB substrate, antennas with a dielectric ceramic backing, and antennas employing different concepts of Rogers substrates. This study also highlights temperature-stable ceramics, which represent a novel development in research, crucial for improving GNSS technology due to their ability to retain a consistent dielectric constant over a broad temperature range; these ceramics eliminate frequency variations in patch and dielectric resonator antennas, guaranteeing precise signal reception, even in extreme outdoor and satellite conditions. Full article

(This article belongs to the Section Polycrystalline Ceramics)

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13 pages, 4560 KB

Open AccessArticle

Effect of Sn on Normalized Texture and Precipitates in Non-Oriented Silicon Steel for New Energy Vehicles

by Yu Zhang, Baozhi Liu, Zhongwang Wu, Huimin Zhang, Xiaolong Zhao, Yanjun Di, Jun Li, Yongquan Han and Huiping Ren

Crystals 2026, 16(5), 347; https://doi.org/10.3390/cryst16050347 - 19 May 2026

Abstract

In the manufacturing process of high-grade non-oriented electrical steel, cast billets are subjected to hot rolling and normalizing treatments. These processes are implemented to optimize the microstructure and texture of steel sheets during production, mitigate corrugated defects, and enhance the magnetic properties of [...] Read more.

In the manufacturing process of high-grade non-oriented electrical steel, cast billets are subjected to hot rolling and normalizing treatments. These processes are implemented to optimize the microstructure and texture of steel sheets during production, mitigate corrugated defects, and enhance the magnetic properties of the final finished sheets. In this study, two types of high-strength non-oriented silicon steel test specimens were prepared via the incorporation of the trace alloying element Sn, namely one without Sn addition and the other with 0.045 wt% Sn. The test specimens were first hot-rolled to a thickness of 2.0 mm, followed by normalization treatment in the laboratory to simulate the continuous normalizing process employed by a domestic steel mill. The effects of Sn on the normalized microstructure, texture, and precipitates of non-oriented silicon steel tailored for new energy vehicles were investigated. The findings reveal that the alloying element Sn can increase the thickness of the recrystallized layer on the surface of hot-rolled sheets and refine the grain size of non-oriented silicon steel. After continuous normalizing treatment, a comparison between the two test specimens shows that as the normalizing temperature rises, the reduction in average grain size of the 0.045 wt% Sn specimen relative to the Sn-free specimen increases from 1.4% to 15.96%. Additionally, the incorporation of Sn reduces the fraction of the {111} texture component (detrimental to magnetic properties) while increasing the fraction of the {100} texture component (beneficial to magnetic properties) in the non-oriented silicon steel. Precipitates exhibited significant coarsening and a reduction in number with increasing temperature, while the addition of Sn exerted a certain inhibitory effect on precipitate growth. Furthermore, the 0.045 wt% Sn-containing test specimen achieved an optimal balance between magnetic and mechanical properties when subjected to normalization at 980 °C and annealing at 920 °C. Under these processing conditions, the magnetic induction B₅₀ reached 1.733 T, the iron loss P_1.5/50 was 2.01 W/kg, the yield strength was 410 MPa, and the tensile strength was 529 MPa. Full article

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

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13 pages, 1552 KB

Open AccessArticle

PS/Al-µPs Surface Modification for Enhanced Optical and Electronic Performance of Multicrystalline Silicon

by Yasmin Zouari, Achraf Manai, Rabia B. Zaghouani, Karim Choubani, Mohammed A. Almeshaal, Wissem Dimassi and Mohamed Ben Rabha

Crystals 2026, 16(5), 346; https://doi.org/10.3390/cryst16050346 - 19 May 2026

Abstract

In this paper, we report on the effect of combining porous silicon with aluminum microparticles (PS/Al-µPs) on the optical and electronic properties of multicrystalline silicon (mc-Si). An aluminum film was deposited on the mc-Si surface, annealed at 750 °C for 20 min, and [...] Read more.

In this paper, we report on the effect of combining porous silicon with aluminum microparticles (PS/Al-µPs) on the optical and electronic properties of multicrystalline silicon (mc-Si). An aluminum film was deposited on the mc-Si surface, annealed at 750 °C for 20 min, and partially remained on the surface after CP₄ treatment. The surface was subsequently treated with a stain-etching solution (HF/HNO₃/H₂O) to form a porous silicon (PS) layer. The resulting mc-Si with PS/Al-µPs modification led to a marked improvement in the optoelectronic performance of the treated mc-Si. Surface reflectance was reduced from 34.6% to 9.1% across 400–800 nm wavelength range, corresponding to a 74% decrease. Minority carrier lifetime increased from 2 µs in untreated samples to 1 ms after Al-µPs passivation and remained elevated at 285 µs following stain etching. Additionally, the effective surface recombination velocity dropped from 50 cm·s⁻¹ to 0.35 cm·s⁻¹ and a reduction in [Fe] after treatment confirms the effectiveness of the PS-Al-µPs gettering process. FTIR analysis confirmed the formation of Si–H and Al–O bonds, highlighting effective surface passivation and suppression of recombination losses. Full article

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19 pages, 1109 KB

Open AccessArticle

Thermal Expansion of Two Copper Vanadates MCu(VO₃)₂Cl (M = Cs, Rb): Structure-Based and Unit-Cell-Based Approaches

by Ilya V. Kornyakov and Vladislav V. Gurzhiy

Crystals 2026, 16(5), 345; https://doi.org/10.3390/cryst16050345 - 18 May 2026

Abstract

Two copper vanadates, MCu(VO₃)₂Cl (M = Cs, Rb), were synthesized and studied by variable-temperature single-crystal X-ray diffraction in the range up to 700 and 675 K for the Cs- and Rb-containing phases, respectively. The structures are composed [...] Read more.

Two copper vanadates, MCu(VO₃)₂Cl (M = Cs, Rb), were synthesized and studied by variable-temperature single-crystal X-ray diffraction in the range up to 700 and 675 K for the Cs- and Rb-containing phases, respectively. The structures are composed of [VO₃] chains of edge-sharing VO₅ polyhedra and [CuO₄Cl] chains of CuO₄Cl₂ octahedra assembled into a three-dimensional framework. Despite close structural similarity, both compounds differ substantially in thermal behavior: the Cs phase exhibits stronger anisotropy compared to the Rb-containing phase. To interpret the structural dynamics, observed bond lengths were compared with values corrected using the simple rigid-body motion model and with bond lengths obtained from TLS analysis of VO₅ polyhedra. It is shown that the observed V–O bond lengths can yield misleading trends, including apparent bond shortening upon heating, whereas rigid-body-corrected values provide a more crystal-chemically consistent picture. In particular, comparison of the observed, SRBM-corrected, and TLS-corrected bond lengths shows that the thermal expansion along the direction of the [VO₃] chains is poorly reflected by the observed bond lengths, whereas the corrected bond lengths exhibit much closer agreement with the thermal expansion derived from the unit-cell parameters. For the other directions, such a comparison is hindered by the geometry of the bridging linkages and by the ambiguity associated with the TLS treatment. The results obtained for MCu(VO₃)₂Cl (M = Cs, Rb) therefore demonstrate the strong influence of bond-length evaluation on the interpretation of structural dynamics. Full article

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

23 pages, 4432 KB

Open AccessArticle

Hydrogen-Rich Mixed Anionic Halides with a Strong Response to UV–Vis Radiations for Photonic and Energy Storage Applications

by Ali Yaqoob, Shamsher Ahmad, Muhammad Usman Khan, Nawishta Jabeen, Ghada A. Alsawah, Muhammad Adnan Qaiser, Hafedh Mahmoud Zayani and Ahmad Hussain

Crystals 2026, 16(5), 344; https://doi.org/10.3390/cryst16050344 - 18 May 2026

Abstract

In this study, density functional theory (DFT)-based investigations are carried out using the CASTEP code. The plane-wave pseudopotential method is used to explore the multifunctional properties, including the structural, electronic spectra, thermo-mechanical and hydrogen storage properties, of hydrogen-rich mixed-anionic (Li₃H₄ [...] Read more.

In this study, density functional theory (DFT)-based investigations are carried out using the CASTEP code. The plane-wave pseudopotential method is used to explore the multifunctional properties, including the structural, electronic spectra, thermo-mechanical and hydrogen storage properties, of hydrogen-rich mixed-anionic (Li₃H₄N₂X, where X = F, Cl, Br, and I) halides. The exchange–correlation interactions are treated within the generalized gradient approximation (GGA) using the Perdew–Burke–Ernzerhof (PBE) functional, while the hybrid HSE06 function is used for accurate band gap predictions. Moreover, the optical properties of the halides are analyzed under the influence of UV–Vis radiation instances. The band gap values of these orthorhombic-structured halides lie in the visible-to-UV regions of radiation, with values of 2.97 eV, 3.12 eV, 3.06 eV and 3.28 eV, respectively. Such band gap values allow these materials to absorb nearly 75% to 90% of incoming radiation, with absorption values around (10⁵ cm⁻¹). These favorable opto-electronic responses make these halides suitable for solar radiation energy conversion applications. Stable thermodynamic responses and the mechanical nature of the mixes (brittle for Li₃H₄N₂Br and ductile for the rest) reveal their practical applicability for flexible photonics. Moreover, due to the presence of rich hydrogen atoms, the Li₃H₄N₂F halide exhibits a gravimetric ratio of around 6.0 wt%, which is higher than the standard (5.5 wt%) value defined by the US DOE. Similarly, GHSC values of 2.5 wt% for Li₃H₄N₂I, 3.5 wt% for Li₃H₄N₂Br, and 5.0 wt% for Li₃H₄N₂Cl are reported; these values indicate that these compounds possess strong potential for use in the hydrogen fuel cells required in light-duty vehicles. Full article

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14 pages, 1186 KB

Open AccessArticle

Mechanical and Surface Characterization of Lithography-Based Ceramic Manufactured Zirconia for Dental Applications

by Abdullah Alshamrani and Majed M. Alsarani

Crystals 2026, 16(5), 343; https://doi.org/10.3390/cryst16050343 - 18 May 2026

Abstract

This study evaluated and compared the mechanical performance of conventionally milled zirconia and two additively manufactured zirconia ceramics fabricated using Lithography-based Ceramic Manufacturing (LCM) technology for potential use in load-bearing dental restorations. A total of 150 zirconia specimens were prepared and allocated into [...] Read more.

This study evaluated and compared the mechanical performance of conventionally milled zirconia and two additively manufactured zirconia ceramics fabricated using Lithography-based Ceramic Manufacturing (LCM) technology for potential use in load-bearing dental restorations. A total of 150 zirconia specimens were prepared and allocated into three material groups: milled zirconia and LCM-printed zirconia (LithaCon 3Y 210 and LithaCon 3Y 230), each subdivided into non-aged (control, C) and thermocycled aged (A) conditions (n = 25 per condition). Specimens were standardized using CAD and fabricated by milling or LCM printing. Flexural strength was assessed using a three-point bending test in accordance with ISO 6872:2024, nanoindentation hardness was measured with a Berkovich indenter following ISO 14577-1:2015, and surface roughness was evaluated using optical profilometry per ISO 21920-2:2021. Flexural strength showed no significant differences among groups, while hardness and surface roughness varied significantly. LCM zirconia demonstrated comparable flexural strength to milled zirconia, although milled materials exhibited higher hardness. The 210A group showed the most favorable overall mechanical profile, warranting further investigation of long-term performance. Full article

(This article belongs to the Special Issue Advances in New Functional Biomaterials for Medical Applications, Second Edition)

10 pages, 1115 KB

Open AccessArticle

Profiling Intermolecular Interactions of Theophylline: Analysis of Some Classes of Theophylline Containing Co-Crystals

by Martin H. Polko and Guido J. Reiss

Crystals 2026, 16(5), 342; https://doi.org/10.3390/cryst16050342 - 18 May 2026

Abstract

Intermolecular interactions play an important role in the formation and stability of co-crystals. In this study, the interaction behaviour of theophylline in co-crystal structures was systematically analysed using data from the Cambridge Structural Database. A total of fifty-three theophylline co-crystal structures were investigated [...] Read more.

Intermolecular interactions play an important role in the formation and stability of co-crystals. In this study, the interaction behaviour of theophylline in co-crystal structures was systematically analysed using data from the Cambridge Structural Database. A total of fifty-three theophylline co-crystal structures were investigated and classified according to their intermolecular interaction motifs. A structured interaction scheme was developed to describe the accessible interaction sites of theophylline, including classical and non-classical hydrogen bonds, as well as halogen bonds and π∙∙∙π interactions. The study revealed theophylline’s high versatility in forming intermolecular interactions, resulting in twenty interaction patterns. Three dominant motifs were identified as occurring most frequently. The results indicate that steric effects influence the accessibility of specific interaction sites, particularly limiting interactions at the carbonyl group located between the two methyl groups. Hirshfeld surface analysis revealed that O∙∙∙H and H∙∙∙H interactions contribute most significantly to the intermolecular interactions in the analysed structures. Full article

(This article belongs to the Section Crystal Engineering)

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16 pages, 4031 KB

Open AccessArticle

Recovery of Lithium from Spent Lithium-Ion Batteries Through Pyrolysis Reduction

by Peng Hu, Haoxiang Wu, Liuli Yao, Jun Yao, Tao Zhang, Siwei Jiang, Xintao Wu, Yazecheng Liu, Jun Li, Peng Dong, Zhongren Zhou and Yingjie Zhang

Crystals 2026, 16(5), 341; https://doi.org/10.3390/cryst16050341 - 18 May 2026

Abstract

In this paper we investigate the use of sucrose as a reducing agent for the carbothermal reduction in spent ternary cathode materials. During this process, lithium from the cathode material is converted into water-soluble Li₂CO₃, while the high-valent transition [...] Read more.

In this paper we investigate the use of sucrose as a reducing agent for the carbothermal reduction in spent ternary cathode materials. During this process, lithium from the cathode material is converted into water-soluble Li₂CO₃, while the high-valent transition metals are reduced to insoluble metallic elements and oxides. The influence of various pyrolysis temperatures, sucrose dosages, and pyrolysis times on the reduction degree of high-valent metals. Furthermore, the influence of leaching conditions on lithium recovery efficiency is examined. Under the optimal conditions of a pyrolysis temperature of 650 °C, a sucrose dosage of 15 wt.%, a pyrolysis time of 30 min, a leaching solid–liquid ratio of 30 g/L, and a leaching time of 30 min, the lithium leaching rate reaches 97.9%. Characterization via XRD, XPS and SEM reveals that sucrose serves as an effective carbothermal reducing agent. It facilitates the reduction of high-valent transition metals to insoluble metallic elements and oxides while simultaneously enabling the recovery of lithium as Li₂CO₃. Consequently, this method achieves an efficient separation of lithium from other metallic elements. Compared to traditional recycling processes, it avoids the low lithium recovery rates often associated with subsequent separation steps. Full article

(This article belongs to the Special Issue Electrode Materials in Lithium-Ion Batteries)

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18 pages, 36073 KB

Open AccessArticle

Processing Route Dependence of Microstructure and Mechanical Properties in an Al-Li-Mg Alloy for Lightweight Sports Equipment

by Ge Liu, Shenchen Zhang, Yuncheng Zhu, Xin Li, Yingchao Zhao, Dengfeng Yin and Ming-Chun Zhao

Crystals 2026, 16(5), 340; https://doi.org/10.3390/cryst16050340 - 18 May 2026

Abstract

The pursuit of lightweight, high-performance sports equipment drives the development of Al-Li-Mg alloys, yet systematic studies linking a complete processing route, from as-cast to peak-aged condition, to microstructural evolution and mechanical properties remain limited. This work provides the first comprehensive investigation of how [...] Read more.

The pursuit of lightweight, high-performance sports equipment drives the development of Al-Li-Mg alloys, yet systematic studies linking a complete processing route, from as-cast to peak-aged condition, to microstructural evolution and mechanical properties remain limited. This work provides the first comprehensive investigation of how a sequential processing route (homogenization, hot rolling, solution treatment, and peak aging) transforms the coarse as-cast structure of an Al-Li-Mg alloy into a refined, recrystallized grain architecture with a uniform dispersion of nanoscale δ′-Al₃Li precipitates. This microstructural transformation leads to a dramatic enhancement in mechanical properties: the peak-aged alloy exhibits increases of approximately 92%, 139%, and 925% in yield strength, ultimate tensile strength, and elongation, respectively, relative to the as-cast condition. The dominant strengthening mechanism is identified as dislocation shearing of coherent δ′-Al₃Li precipitates (average radius ~5 nm, well below the ~25 nm transition threshold for Orowan looping), which enhances strength without compromising ductility, demonstrating the critical role of the processing route in tailoring microstructures and mechanical properties for lightweight sports equipment. Full article

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

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5 pages, 167 KB

Open AccessEditorial

Synthesis, Crystal Structures and Hirshfeld Surface Analysis of Coordination Compounds (3rd Edition)

by Waldemar Maniukiewicz

Crystals 2026, 16(5), 339; https://doi.org/10.3390/cryst16050339 - 18 May 2026

Abstract

The third edition of the Special Issue of Crystals, entitled “Synthesis, Crystal Structures and Hirshfeld Surface Analysis of Coordination Compounds”, continues to serve as a high-profile forum for researchers to share their latest findings in the field of coordination chemistry [...] Full article

(This article belongs to the Special Issue Synthesis, Crystal Structures and Hirshfeld Surface Analysis of Coordination Compounds (3rd Edition))

17 pages, 1506 KB

Open AccessArticle

Exploring Monohalogen-Substituted Phenylethylamine Hydro-Chloride Salts: Preparation and Solid Phase Analysis of Pharma-Ceutical Building Blocks and Resolving Agents

by Sven Tiedemann, Wilko Fokken, Heike Lorenz and Jan von Langermann

Crystals 2026, 16(5), 336; https://doi.org/10.3390/cryst16050336 - 17 May 2026

Abstract

Monohalogen-substituted (F-, Cl-, Br-) phenylethylamine derivates are a valuable class of chiral compounds, e.g., for C-C-coupling reactions, which are the basis for multiple pharmaceuticals and resolving agents. Here, the solid phase behavior of the underlying phenylethylamine derivates, especially of the corresponding hydrochloride salts, [...] Read more.

Monohalogen-substituted (F-, Cl-, Br-) phenylethylamine derivates are a valuable class of chiral compounds, e.g., for C-C-coupling reactions, which are the basis for multiple pharmaceuticals and resolving agents. Here, the solid phase behavior of the underlying phenylethylamine derivates, especially of the corresponding hydrochloride salts, is highly relevant as those compounds are often applied in enantiopure form during the production processes. In this study, the solid phase behavior of 20 synthesized chiral phenylethylamine hydrochloride derivates (both enantiomers and racemates) was investigated including detailed information regarding melting behavior, powder X-ray diffraction data and the type of the chiral system present. Further, the binary melt phase diagram of a found conglomerate system and two novel enantiomer crystal structures were determined. This study is aimed at revealing structure–phase behavior relationships for the 20 monohalogen-substituted compounds investigated as well as providing basic solid–phase-related data required for later crystallization-based enantioseparation processes. Full article

14 pages, 3986 KB

Open AccessArticle

Enhanced Properties of Electrodes Based on Ti/TiO₂-Au/rGO Composite Structures for Electrochemical Application

by Cornelia Bandas, Mina-Ionela Morariu, Corina Orha, Carmen Lazau and Mircea Nicolaescu

Crystals 2026, 16(5), 338; https://doi.org/10.3390/cryst16050338 - 16 May 2026

Abstract

The increasing environmental pollution with emergent pollutants has led to the necessity to develop various structures for sensory applications used in water monitoring processes. In this context, this study presents a composite structure based on titanium foil/titanium dioxide/reduced graphene oxide functionalized with gold [...] Read more.

The increasing environmental pollution with emergent pollutants has led to the necessity to develop various structures for sensory applications used in water monitoring processes. In this context, this study presents a composite structure based on titanium foil/titanium dioxide/reduced graphene oxide functionalized with gold ions (Ti/TiO₂-Au/rGO) obtained by a simple and efficient spin-coating method, successfully applied in electrochemical doxorubicin detection processes. The synthesis protocol first involves etching the titanium foil to form a Ti/TiO₂ substrate, followed by the synthesis of the TiO₂-Au/rGO solution, which was deposited by a spin-coating technique on the surface of the Ti/TiO₂ support, to form electrodes based on a Ti/TiO₂-Au/rGO composite structure. The structure and morphology of the as-synthesized composites were investigated in detail using X-ray analysis, Raman spectroscopy, and scanning electron microscopy coupled with an EDX. Furthermore, to determine the electroactive surface area and apparent diffusion coefficient of the composite structures, the electrochemical behavior was evaluated by CV in a 1 M KNO₃ and in the presence of 4 mM K₃Fe(CN)₆. By using electrochemical impedance spectroscopy (EIS) in 0.1 M NaOH supporting electrolyte and within a frequency range of 0.1–10,000 Hz and a voltage of 10 mV, the charge transfer resistance was also investigated. The potential application in electroanalysis of the electrodes was tested by CV for the detection of the DOX pollutant in 0.1 M NaOH and 1–5 mg L⁻¹ DOX. The obtained results provide new insights into the development of electrochemical sensors for applications in water treatment processes. Full article

(This article belongs to the Special Issue Synthesis and Applications of Crystalline Nanoporous Materials)

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13 pages, 2534 KB

Open AccessArticle

Slower Load-Dependent Increase and Logarithmic Rate Dependence of Friction in Suspended WS₂

by Ketong Zhang, Haoran Yao, Jianheng Sun, Xiaosen Ren, Zhifei Yao, Bohui Zhao, Qiuyuan Sun, Jiuyan Wei, Qiang Zhu, Hao Guo, Zhonghao Li, Xin Li, Huanfei Wen, Jun Tang, Yanjun Li, Sugawara Yasuhiro, Zongmin Ma and Jun Liu

Crystals 2026, 16(5), 337; https://doi.org/10.3390/cryst16050337 - 16 May 2026

Abstract

Suspended two-dimensional (2D) materials in high-performance devices exhibit unique properties that are critically important for nanoscale mechanical and electromechanical applications, while their frictional laws remain poorly understood. Here, we investigate the nanoscale frictional behavior of suspended WS₂ flakes under varying applied loads [...] Read more.

Suspended two-dimensional (2D) materials in high-performance devices exhibit unique properties that are critically important for nanoscale mechanical and electromechanical applications, while their frictional laws remain poorly understood. Here, we investigate the nanoscale frictional behavior of suspended WS₂ flakes under varying applied loads and scanning rates using atomic force microscopy (AFM), and successfully employ the Bowden–Tabor theory and the thermally activated Prandtl–Tomlinson (PTT) model to analyze the load- and scanning-rate-dependent friction characteristics of suspended 2D systems. The results show that suspended WS₂ exhibits higher friction than supported WS₂, whereas its friction increases more slowly with applied load, which can be well described by the Bowden–Tabor theory. Moreover, the friction exhibits a logarithmic dependence on scanning rate for both suspended and supported WS₂. Quantitative analysis within the framework of the PTT model demonstrates that this model can be successfully extended to describe the rate-dependent friction of suspended WS₂, providing a unified framework for both supported interfaces and suspended 2D systems. This work provides valuable guidance for understanding frictional dissipation mechanisms relevant to the design and optimization of WS₂-based devices. Full article

(This article belongs to the Section Inorganic Crystalline Materials)

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29 pages, 3860 KB

Open AccessReview

Unraveling the Underlying Mechanism of the Li⁺ Migration Inside Halide Solid-State Electrolytes: Structural Tuning and Defect Manipulation

by Yiqiao Xu, Jingzheng Weng, Qiyong Li, Ting Luo and Yi Zhang

Crystals 2026, 16(5), 335; https://doi.org/10.3390/cryst16050335 - 15 May 2026

Abstract

Halide-based solid electrolytes have emerged as promising candidates for next-generation all-solid-state lithium metal batteries due to their high room-temperature ionic conductivity, wide electrochemical stability window, and favorable mechanical properties. This review provides a comprehensive overview of the fundamental structure–property relationships, Li⁺ transport [...] Read more.

Halide-based solid electrolytes have emerged as promising candidates for next-generation all-solid-state lithium metal batteries due to their high room-temperature ionic conductivity, wide electrochemical stability window, and favorable mechanical properties. This review provides a comprehensive overview of the fundamental structure–property relationships, Li⁺ transport mechanisms, and performance optimization strategies for Li₃MX₆-type halide solid electrolytes. The unique structural framework of halide electrolytes, characterized by close-packed anion sublattices (hexagonal close-packed and cubic close-packed) and edge-sharing [MX₆]³⁻ octahedral networks, establishes three-dimensional Li⁺ percolation pathways with low migration barriers (0.20–0.33 eV). This review concludes by identifying key challenges and future research directions, including high-entropy halide design, scalable aqueous synthesis methods, earth-abundant material alternatives, and integrated cell architectures that combine halide catholytes with complementary anolyte materials for practical all-solid-state battery applications. Full article

(This article belongs to the Section Materials for Energy Applications)

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21 pages, 11691 KB

Open AccessArticle

Microstructural Evaluation of Plasma-Vitrified Wind Turbine Blade Slag and Its Alternative Application in Geopolymer

by Vilma Snapkauskienė, Regina Kalpokaitė-Dičkuvienė, Arūnas Baltušnikas and Viktorija Grigaitienė

Crystals 2026, 16(5), 334; https://doi.org/10.3390/cryst16050334 - 15 May 2026

Abstract

With the rapid expansion of wind energy infrastructure, there is an increasing accumulation of wind turbine blade waste (WTBW), which is mainly composed of glass fiber-reinforced thermosetting composites. Due to the irreversible nature of polymer crosslinking, conventional recycling methods remain limited. In this [...] Read more.

With the rapid expansion of wind energy infrastructure, there is an increasing accumulation of wind turbine blade waste (WTBW), which is mainly composed of glass fiber-reinforced thermosetting composites. Due to the irreversible nature of polymer crosslinking, conventional recycling methods remain limited. In this study, plasma vitrification was employed to convert WTBW into a reactive calcium-aluminum-silicate slag suitable for use in geopolymer materials. Plasma treatment at a temperature of approximately 2750 K resulted in the formation of predominantly amorphous vitrified slag (VS). Structural characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) revealed the spatial heterogeneity of the VS. This heterogeneity was influenced by thermal gradients and varied between samples collected from different slag discharge zones, both vertically and horizontally from the reactor. All VS samples contained between 30 and 89% amorphous phase and 10–55% anorthite, with the proportions varying by sampling location. Chemical stability tests showed the dissolution of calcium and aluminum in acidic media, resulting in a silica-enriched residual structure in which the Ca and Al content decreased to less than 0.5 at.% after 100 days. In contrast, exposure to alkaline media caused only minimal surface reorganization—the addition of 5 wt.% VS to acid-based geopolymers made with two metakaolin precursors resulted in a 35% decrease in the mechanical strength of pure metakaolin-based systems. In contrast, when metakaolin containing illite impurities was used, strength values were similar to those of the reference geopolymer. The results quantitatively demonstrate that plasma-derived slag exhibits composition-dependent reactivity, directly linked to its amorphous content and dissolution behavior. 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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12 pages, 299 KB

Open AccessArticle

Flexoelectric Instability in Bent-Core Nematic Liquid Crystals

by Ahlam Almamari and Mikhail Osipov

Crystals 2026, 16(5), 333; https://doi.org/10.3390/cryst16050333 - 15 May 2026

Abstract

We develop a theoretical model for the flexoelectric instability in bent-core nematic liquid crystals, focusing on the coupling between elastic distortions and an external electric field through flexoelectric polarization. The analysis is carried out in the nematic phase close to the twist-bend transition, [...] Read more.

We develop a theoretical model for the flexoelectric instability in bent-core nematic liquid crystals, focusing on the coupling between elastic distortions and an external electric field through flexoelectric polarization. The analysis is carried out in the nematic phase close to the twist-bend transition, where both the flexoelectric coefficients and the effective bend elastic constant exhibit strong temperature dependence. Within a Landau–de Gennes framework, we derive analytical expressions for the threshold electric field and the corresponding wave vector of the emerging periodic modulation by minimizing the total free energy and assuming

K_{1} = K_{2}

. Numerical simulations illustrate the temperature dependence of the threshold parameters and the role of dielectric anisotropy and elastic constants. The results indicate that the flexoelectric instability may occur only within a finite temperature interval above the transition into the twist-bend phase and that both the threshold electric field and the periodic structure’s wave vector decrease as the temperature decreases. Full article

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

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24 pages, 4570 KB

Open AccessArticle

Empirical Screening of Two Laser Processing Conditions with Respect to Graphitic Ordering and Electrochemical Performance of PEI-Derived Laser-Induced Carbon

by Pamela Rivera Rivera, Šarūnas Mickus, Aušra Selskienė, Tomas Murauskas, Sandra Stanionytė, Romualdas Trusovas, Justina Gaidukevič and Rasa Pauliukaite

Crystals 2026, 16(5), 332; https://doi.org/10.3390/cryst16050332 - 15 May 2026

Abstract

Laser-induced graphene (LIG) enables rapid conversion of polymer substrates into conductive carbon materials. In this study, nitrogen-containing carbon nanomaterials were fabricated on polyetherimide (PEI) substrates using empirical screening of two specific process points. The resulting materials were characterized using scanning electron microscopy, Raman [...] Read more.

Laser-induced graphene (LIG) enables rapid conversion of polymer substrates into conductive carbon materials. In this study, nitrogen-containing carbon nanomaterials were fabricated on polyetherimide (PEI) substrates using empirical screening of two specific process points. The resulting materials were characterized using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy to correlate structural features with electron-transfer behavior. Raman and XPS analyses showed different structure and morphology depending on irradiation regime. The carbon materials with a higher sp³ fraction (≈55–59%), larger in-plane crystallite size (L_a up to 8.0 nm), and pronounced π–π* shake-up satellites indicated enhanced graphitic ordering when a shorter nanosecond laser was used. These structural differences resulted in substantially lower charge-transfer resistance (0.53–0.79 kΩ·cm³) and larger electroactive surface areas for the porous electrodes compared with foam structured carbon nanomaterials. The results show that, under the selected fabrication conditions, variations in laser processing parameters correspond to differences in graphitic ordering and electron-transfer properties in PEI-derived laser-induced carbon materials. Full article

(This article belongs to the Special Issue Functional Nanomaterials for Electrochemical Sensing and Energy Storage)

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