Solids doi: 10.3390/solids7050052

Authors: Senlin Li Ningwei Zuo Jinbao Zhang Xueqiang Yang Yuxuan Sun

Beryllium-tungsten (Be-W) intermetallic compounds are promising candidates for fusion-reactor plasma-facing components and aerospace high-temperature structural materials owing to their low density, high elastic modulus, high melting point and excellent irradiation-corrosion resistance. Nevertheless, experimental acquisition of intrinsic physical properties for single-phase Be-W intermetallics remains challenging because of significant differences in the melting points of constituent elements and the tendency for elemental segregation during preparation. In this paper, first-principles calculations based on density functional theory with the GGA-PBE functional were performed to investigate the crystal structure, thermodynamic stability, electronic bonding and mechanical properties of Be2W, Be12W, and Be22W. The results reveal that Be12W has the lowest formation enthalpy and exhibits the strongest phase-forming ability, while Be2W shows relatively poor thermodynamic stability. All three phases are metallic with no band gap, and their bonding exhibits strong Be-p–W-d orbital hybridization with partial covalent features on the basis of metallic bonding. According to the Born–Huang stability criteria, Be2W, Be12W and Be22W are all mechanically stable. Be2W possesses superior resistance to volumetric deformation; Be12W achieves the highest shear modulus, Young’s modulus and theoretical Vickers hardness, but displays relatively high brittleness; Be22W has low elastic modulus and hardness within the range of 2–8 GPa, indicating favourable machinability yet insufficient structural stability. Comprehensive analysis demonstrates that Be12W is the optimal target phase for high-temperature irradiation-resistant Be-W-based structural materials. This work clarifies the structure–property relationships of Be-W intermetallics and provides theoretical support for composition optimization, phase regulation and experimental development of relevant advanced materials.

Solids doi: 10.3390/solids7050051

Authors: Fatemeh Mollaamin Majid Monajjemi

The electronic-structure traits of titanium (Ti), chromium (Cr), manganese (Mn), and nickel (Ni) doped-zinc sulfide (ZnS) through H2O molecule adsorption were investigated using first-principles studies. A detailed study was performed using density functional theory (DFT) calculations at the CAM-B3LYP-D3/6-311+G (d,p) level to investigate how H2O is captured by a ZnS, ZnSTi, ZnSCr, ZnSMn, or ZnSNi nanostructure. The shape of binding of hydrogen or hydroxyl groups to the surface of a ZnS, ZnSTi, ZnSCr, ZnSMn, or ZnSNi nanostructure could produce a weak signal close to the edge of the surface. This thought was accompanied by delving into the density of states, consisting of total, partial, and orbital-projected density of states, as well as electrostatic potential, for both the bare and water-covered surfaces of ZnS, ZnSTi, ZnSCr, ZnSMn, and ZnSNi. From this, it can be considered that Zn, Ti, Cr, Mn, and Ni in these complexes have a better capability to take in electrons when water is captured. These outcomes propose that the electronic properties of these complexes can be altered by controlling where water is absorbed on their surfaces. The target of this investigation is to detect routes to treat water and ameliorate the performance of titanium zinc sulfide, chromium zinc sulfide, manganese zin sulfide, and nickel zinc sulfide alloys as photocatalysts for wiping contaminants.

Solids doi: 10.3390/solids7050050

Authors: Michael A. Gebremichael Belete S. Yigezu Girma T. Chala

Nowadays, carbonized natural fiber composites are sustainable alternatives for electromagnetic wave absorption in unmanned aerial vehicles (UAVs). However, achieving a balance between electromagnetic performance, structural thickness, and weight is still difficult. This study, therefore, presents a multi-objective optimization framework for designing a lightweight radar-absorbing multilayer composite using a carbonized false banana fiber/Fe3O4 hybrid absorber. In this work, a four-layer sandwich panel was modeled in SOLIDWORKS 2017 and analyzed using full-wave electromagnetic simulation in ANSYS HFSS (R18.1) over the frequency range of 2–18 GHz. Layer thicknesses were optimized using a multi-objective particle swarm optimization (MOPSO) algorithm with three objectives: maximizing the frequency-averaged power absorptivity, minimizing panel mass, and minimizing total thickness. The objectives were handled simultaneously through Pareto dominance without predefined weighting coefficients, and a compromise solution was selected from the resulting Pareto-optimal set. The selected Pareto compromise was subsequently adjusted considering practical layer-thickness and manufacturability requirements, resulting in a 2/5/2/1 mm multilayer configuration with a total thickness of 10 mm. The resulting configuration achieved frequency-averaged power absorptivities of 0.6756 over 2–18 GHz and 0.8289 within the Ku-band, together with an effective absorption bandwidth of 3.2 GHz for power absorptivity above 90%. A minimum reflection coefficient magnitude of 0.0230 (corresponding to a peak power absorptivity of 99.95% at resonance) was obtained, with a minimum reflection loss of −32.75 dB. The optimized panel achieved a mass of 0.1725 kg, corresponding to a modest 1.42% reduction relative to an equal-footprint, equal-thickness monolithic carbon-fiber reference panel. These numerical results show the potential of combining a biomass-derived absorber with multi-objective optimization for the preliminary design of UAV-oriented radar-absorbing multilayer structures.

Solids doi: 10.3390/solids7050049

Authors: Anamika Poduval Mark Granier Roshni Bhuvan Levon A. LeBan C. Merry Harpin Steven W. Rick John B. Wiley

The Dion–Jacobson perovskite solid acid, HLaNb2O7, is an important intermediate in many topochemical reactions such as those involving ion exchange, intercalation, exfoliation, and grafting. Rietveld structure refinement of time-of-flight neutron diffraction data (7.66 K, P4/mmm, a = b = 3.8907(3) Å, c = 10.5068(9) Å) shows that protons bridging across the HLaNb2O7 interlayer serve to align LaNb2O7 blocks through NbO6 apical oxygens. The oxygens are 2.54 Å apart, with the intermediate proton distributed over two half-occupied sites, and 1.15(10) Å from the closest oxygen. Such short strong hydrogen bonds are shorter (1.40 Å) than are typical for many known mixed metal oxide solid acids (ca. 2.8 Å–3.5 Å). Anisotropic refinement of the hydrogen thermal parameter reveals an elongation suggesting an active hydrogen that moves between the two oxygens, O–H…O ↔ O…H–O; DFT modeling supports this behavior, finding a minimal activation energy between two states; and infrared studies (FTIR) exhibit a broad low-energy band at ~1600 cm−1, associated with the hydrogen resonance between the apical oxygens. These results are discussed in terms of structure, strong low-barrier hydrogen bonding, and proton mobility.

Solids doi: 10.3390/solids7050048

Authors: William Aperador Jose Luis Caballero Giovany Orozco-Hernández Christian Ortiz Julio C. Caicedo

β-Type titanium alloys mitigate stress shielding through their low elastic modulus, but their limited wear resistance restricts their use in articulating surfaces. This study evaluated the effect of a 100 nm Au interlayer on the structural, electrochemical, tribocorrosion and biological behaviour of TaN coatings deposited by magnetron sputtering on aged Ti-13Nb-13Zr. Coatings were characterised by XRD, SEM and AFM and assessed by potentiodynamic polarisation, electrochemical impedance spectroscopy and ASTM G119 tribocorrosion tests in Ringer’s lactate at 37 °C, ICP-MS, and MTT and LDH assays with MG-63 cells. Both coatings were columnar and dominated by δ-TaN; the interlayer attenuated the ε-TaN and γ-Ta2N phases and increased the crystallite size from 24 ± 3 to 31 ± 2 nm. The TaN/Au system shifted the corrosion potential from −210 ± 18 to +35 ± 10 mV vs. Ag/AgCl and lowered the corrosion current density 23-fold. Under tribocorrosion, the friction coefficient fell from 0.28 to 0.17, the wear volume fell 7.2-fold and the synergistic fraction fell from 35% to 14%. Ti release fell from 1.85 to 0.16 µg·cm−2 and 72 h cell viability rose from 82 ± 5% to 96 ± 3%. A nanometric noble interlayer is therefore a promising strategy for articulating surfaces of β-titanium alloys.

Solids doi: 10.3390/solids7050047

Authors: Alessio Langiu Giacomo Canale Felice Rubino

Ceramic-matrix-composite (CMC) turbine seal segments lose their gas-side coatings in service. Assessing one loss configuration takes a thermal and a mechanical finite-element solve, and there are too many admissible configurations to solve them all. A surrogate makes it affordable and follows it as the loss progresses. We build one on 5452 solves of a published seal-segment model with coating added, specify its toolchain in full, and compare four digital-twin techniques: a neural network against reduced-basis and full-field Gaussian processes. Swapping a lost cell to a higher-conductivity material instead of deleting it costs about 1 °C in the mean but 100 °C at the rim, an error that stays on the sacrificial coating and under-reads the substrate by at most 11.5 °C. That error is one-signed: a bias to be carried, not a scatter. On a reduced basis the basis binds, not the regressor: neither model improves with data. Restricting the design to the service-marked loss zones is worth 3.4× on one layer and 3.1 to 4.9× on two. The recommended full-field twin returns the peak coating-interface temperature within 0.23 °C at 3 ms per pattern, but a free superposition baseline beats it in the maintenance regime.

Solids doi: 10.3390/solids7050046

Authors: Sapargali Pazylbek Turlybek N. Nurakhmetov Temirulan T. Alibay Batsay M. Sadykova Aidana A. Shakhantayeva Berdibek Shaizada Olzhas Shalkhar Aleksej Zarkov Aivaras Kareiva

In YPO4:Bi irradiated with photons in the energy range of 5.5–6.2 eV and with X-rays, sensitization-related luminescent states are formed in the 4.43–3.35 eV energy range, appearing as a broad emission band. The excitation spectrum of this broad band lies in the photon-energy range of 5.9–6.2 eV. As in many phosphor materials, these sensitization-related luminescent states are formed as a result of charge transfer from an excited host anion to neighboring ions and impurity centers introduced into the lattice, leading to the formation of electron-trapping centers. Upon excitation of irradiated YPO4:Bi with photons in the energy range of 4.43–3.35 eV, two groups of emission bands are observed: at 3.1–2.9 eV and at 2.8–2.25 eV. These emissions are excited within two spectral regions, from 4.43 to 3.8 eV and from 3.7 to 3.25 eV, and appear as several recombination-related bands. Reflectance spectrum measurements show that, within the transparency region of the host matrix, additional energy levels appear in the 4.43–3.35 eV spectral range. Excitation through these levels gives rise to the observed recombination luminescence, and their energy positions correspond to the excitation spectra of the respective recombination emission bands.

Solids doi: 10.3390/solids7050045

Authors: Wellington Jesus Thamires Reis Luane Marques Héricles Souza Eduardo Lima Adrina Silva

Commercially produced as-cast AM50 magnesium alloy was investigated to assess the relationship between cast microstructural heterogeneity, local hardness contrast, tensile variability, and fracture behavior. Optical microscopy (OM), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD), semiquantitative image analysis, hardness testing, tensile testing, and fractography were employed. The microstructure was dominated by an α-Mg matrix containing interdendritic Al-enriched constituents consistent with β-Mg17Al12 and Al–Mn-rich particles. XRD confirmed α-Mg and β-Mg17Al12, whereas the Al–Mn-rich constituents were supported by SEM/EDS but could not be reliably indexed by XRD. Image analysis of eight optical fields yielded an apparent area fraction of 27.6 ± 1.1% for dark interdendritic/secondary regions; this value represents combined etched microstructural constituents rather than an individual phase fraction. Vickers microhardness showed a pronounced local contrast between the matrix (39.1 ± 5.3 HV) and constituent-rich regions (119 ± 12 HV). Tensile testing of six specimens extracted from comparable upper regions of different commercial ingots yielded an average ultimate tensile strength of 129.42 ± 17.63 MPa, while recorded fracture strain showed substantially greater relative scatter (coefficient of variation ≈122%) than strength. Fractography revealed mixed ductile–brittle features, including dimples, tear ridges, and localized brittle or rough regions. The combined results show that intermetallic-rich regions contribute to local mechanical heterogeneity, but their presence alone is insufficient to explain the tensile variability. Casting-related discontinuities, sampling history, and between-ingot variability must also be considered.

Solids doi: 10.3390/solids7050044

Authors: Mihai Buțu Petru Moldovan Lucian Roșu Nicolae Șerban Andrei Constantin Berbecaru Florin Baciu Constantin-Domenic Stăncel Larisa Buțu Marinela Marinescu Florentina Niculescu Gheorghe Iacob

The paper presents thermodynamic data for the aluminothermic reaction used to synthesise hybrid composites (Al3Zr, ZrB2)/AA6063. AA6063 alloy was used with K2ZrF6, KBF4 and Na3AlF6 as precursors. Composites containing 2.5, 5, 7.5 and 10% wt.% ZrB2 were produced by direct melt reaction at 900 °C and characterised by optical microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD). The effect of the salt addition level on the resulting structures is also reported. The compressive behaviour was evaluated at room temperature to an engineering strain of 75% and complemented by tensile tests. The mechanical response is non-monotonic with reinforcement content: the flow stress decreases slightly between 2.5 and 7.5 wt.% ZrB2 and recovers at 10 wt.%, reaching 321.5 MPa at 30% engineering strain against 278.2 MPa for the matrix. The thermodynamic data and microstructural analysis presented here describe the aluminothermic reaction and its effect on the resulting composites.

Solids doi: 10.3390/solids7050043

Authors: Mingqi Gao An Zhang Yueyou Yang Tong Hu Chunlei Dang Lin Zhao Yagang Zhang

To meet the demands for high-density integration and broadband RF performance in next-generation electronic equipment, this paper investigates the structural design and process sensitivity of vertical interconnects in three-dimensional stacked system-in-package (3D-SiP). Based on quasi-coaxial matching and low-impedance compensation techniques, three typical vertical interconnect structures are designed: the PCB-BGA-SiP microstrip structure achieves S11 better than −15 dB and S21 < 0.3 dB within 2–20 GHz; the lower stripline–BGA–upper microstrip structure achieves S11 better than −27 dB; the lower microstrip–BGA–upper microstrip structure achieves S11 better than −18 dB within 1–23 GHz. Isolation simulation shows that the isolation between adjacent channels exceeds 55 dB within 25 GHz. For process sensitivity evaluation, physical samples of gold wire bonding parameters (length, diameter, number) were fabricated and tested for S11, confirming that the dual-wire topology extends the effective bandwidth to 2–20 GHz (a 54% improvement over single wire), the third-wire marginal gain is only ~5%, and 25 μm diameter offers the best overall performance. For BGA ball radius and pad pitch, parametric sensitivity analysis via Ansys HFSS was performed (not experimentally validated process variation results), identifying the optimal BGA radius as 0.245 mm with an allowable variation of ±0.015 mm, and the pad center-to-center distance should be controlled near 0.8 mm. Based on these findings, process control strategies are proposed: low-loop wire bonding (loop height < 50–80 μm) with statistical process control; substrate warpage controlled through symmetric copper filling, a thick-middle dielectric stack-up, and distributed symmetric cavity layout, combined with eutectic pressure of 1.5 kPa, validated on 10 fabricated substrates with peak warpage consistently < 80 μm, void rate 4.75%, and solder overflow 94%; and BGA soldering using high-precision vision alignment and controlled collapse (20–35%). This work provides a theoretical basis and practical process pathway for transitioning 3D-SiP vertical interconnects from ideal design to mass production.

Solids doi: 10.3390/solids7050042

Authors: José Vieira da Silva Neto Javier Sierra Gómez Johnny Ferraz Dias Alexandre M. Zaitsev Evaldo José Corat Vladimir Jesus Trava-Airoldi

This study investigates the formation and evolution of nitrogen-vacancy (NV) centers in nitrogen-doped CVD diamonds. The diamonds were grown via the microwave plasma-assisted chemical vapor deposition (MPACVD) method with different levels of nitrogen doping, then irradiated with helium and hydrogen ions at different energies and doses, followed by low-pressure, high-temperature (LPHT) annealing at 1300 °C and 1400 °C. The presence and intensity of NV0 and NV− centers were identified and tracked by photoluminescence spectroscopy after each step. The results showed that both helium and hydrogen irradiation could induce NV center formation, with variation in NV0/NV− charge states depending on the irradiation conditions. Helium-irradiated samples generally exhibited stronger NV− signatures; however, the hydrogen-irradiated sample 5N10 (3 MeV, 1 × 1013 ions/cm2) displayed the most pronounced NV− presence of all samples, highlighting the critical role of nitrogen content and irradiation parameters. Ion irradiation reduced internal hydrostatic stress in all samples—from up to +0.23 GPa (compressive) in N5 and down to −0.82 GPa (tensile) in N10—relaxing stress toward near-zero values while increasing the Raman FWHM from ~3.5 cm−1 to up to 6.7 cm−1, indicating lattice disorder. LPHT annealing at 1300–1400 °C significantly increased NV-related photoluminescence, indicating effective thermal activation of vacancy-nitrogen recombination. Complementary Raman and FTIR analyses were employed to assess stress and defect evolution. The methodology enabled a comprehensive evaluation of the effects of irradiation and annealing on diamond defect structures, providing relevant experimental data for the controlled engineering of NV centers for quantum technologies.

Solids doi: 10.3390/solids7050041

Authors: Jingdong Lei Jiabao Li Jianling Huang

The use of Mg-based alloys as anode materials in nickel–metal hydride (Ni–MH) batteries is significantly limited by rapid capacity loss during charge–discharge cycles. This study conducts a comprehensive examination of how variations in the concentrations of Mg and Pd impact the microstructural characteristics and electrochemical behavior of Mg–Pd–Ni ternary alloys, aiming to enhance cyclic durability and uncover the fundamental degradation mechanisms. This work demonstrates that increasing the Mg content tends to reduce the reversibility of electrochemical hydrogenation/dehydrogenation reactions and exacerbates the corrosion behavior of the milled Mg–Pd–Ni alloy electrodes, thus accelerating their capacity decay. On the contrary, raising the Pd content contributes to improving the reversibility of electrochemical hydrogenation/dehydrogenation reactions and the kinetic behavior of the alloys, yet it does not enhance corrosion resistance.

Solids doi: 10.3390/solids7040040

Authors: Andrey Escala Alves Pablo Leite Bernardo Thalis Custódia Cordeiro Roberto da Trindade Faria José Nilson França de Holanda

Calcium niobate ceramics were synthesized by the solid-state reaction of seashell-derived CaCO3 and Nb2O5 at a molar ratio of 4:1 over the temperature range of 800–1200 °C for 8 h. This work provides a correlated structural, morphological, and thermophysical characterization of the resulting calcium niobate phases. X-ray diffraction coupled with Rietveld refinement revealed a temperature-dependent phase transformation from a CaNb2O6-rich composition at lower synthesis temperatures to a Ca4Nb2O9-rich material at higher temperatures. At 1200 °C, Ca4Nb2O9 was obtained as the predominant phase (96.16 ± 1.81%), with only a minor Ca2Nb2O7 contribution. This phase evolution was accompanied by an increase in the Ca4Nb2O9 crystallite size from 39.49 ± 0.19 nm at 1000 °C to 50.38 ± 0.24 nm at 1200 °C. SEM analysis showed a concurrent morphological transformation from agglomerated and irregular particles to well-defined elongated and platelet-like particles, indicating enhanced crystallization and grain growth. Thermophysical properties were determined using open photoacoustic cell and laser-flash techniques. Thermal diffusivity ranged from 1.86 to 3.12 × 10−7 m2 s−1, heat capacity from 0.79 to 1.30 × 104 JK−1 m−3, thermal conductivity from 0.15 to 0.41 Wm−1 K−1, and thermal effusivity from 0.36 to 0.73 kWs1/2 m−2 K−1. The combined results establish a clear synthesis–structure–property relationship and identify the Ca4Nb2O9-rich ceramic obtained at 1200 °C as a promising low-thermal-conductivity material. The use of seashell waste additionally provides a renewable calcium precursor for the synthesis.

Solids doi: 10.3390/solids7040039

Authors: Willian Aperador Giovany Orozco-Hernández Julio Cesar Caicedo

Ultra-high-temperature ceramic (UHTC) coatings offer a promising route to extending cutting tool service life under severe conditions. This work evaluates the tribological behaviour and wear regime transitions of ZrB2–SiC/ZrO2 coatings, deposited by physical vapour deposition (PVD) onto ASSAB-17 high-speed steel tool bits, during dry turning of Ti-6Al-4V. Structural, microstructural, mechanical, and tribological characterisation was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), nanoindentation, and pin-on-disc testing under three pressure–velocity (PV) severity levels, with worn surfaces analysed by SEM and profilometry. The coating exhibited a nanostructured ZrB2/β-SiC/t-ZrO2 architecture with a hardness (H) of 24 ± 3 GPa, a hardness-to-reduced-elastic-modulus ratio (H/Er) of 0.100, and an elastic resistance to plastic deformation (H3/Er2) of 0.240 GPa. Three tribological regimes were identified: running-in, steady-state sliding, and progressive degradation, with the highest severity (PV = 6.0 N·m/s) triggering degradation beyond approximately 620 m, a more than one-order-of-magnitude rise in wear rate, and the only case exceeding the tool-life criterion of maximum flank wear (VBmax = 0.30 mm) according to ISO 3685. The main advantage of the proposed approach is that it condenses tool-life-relevant behaviour into a single, easily measurable severity parameter, the PV product, directly applicable to coating design and the selection of safe machining-condition windows. The overall behaviour is consistent with a mechanism governed by the stability and regeneration capacity of a protective tribofilm. As the composition of this layer was not directly characterised, this mechanism is proposed as a phenomenological interpretation, from which a PV threshold is derived as a design criterion for UHTC coatings.

Solids doi: 10.3390/solids7040038

Authors: Hwan Jung Jang-Ho Jay Kim

Enclosed reinforced concrete structures subjected to internal blast loading represent a critical safety concern in infrastructure applications where detonations may occur within confined spaces. Although circular cross-sections have been widely adopted for blast-resistant containment structures, systematic quantitative comparisons of internal blast responses between circular and square enclosed configurations under progressive charge weight conditions remain limited. LS-DYNA finite element simulations are conducted under four trinitrotoluene (TNT) charge weight conditions ranging from 1200 to 2500 kg, and the failure-inducing blast load is defined as the minimum charge weight at which continuous concrete element deletion first occurs in the roof or side-wall region. In this study, the failure-inducing blast load is interpreted as an erosion-based comparative indicator under the adopted empirical blast-loading framework rather than as an absolute real-world confined-blast failure threshold. The roof failure-inducing blast load is identical for both structures at 1200 kg, whereas the side-wall failure-inducing blast loads are 2500 kg for the circular structure and 1500 kg for the square structure, indicating approximately 67% higher side-wall blast resistance in the circular structure. This difference is attributed to the membrane action of the curved wall, which redistributes internal blast-induced lateral pressure along the circumferential direction and limits out-of-plane deformation. Under the 2500-kg condition, the peak side-wall displacement of the square structure is 161.6% higher than that of the circular structure, whereas its peak roof displacement is 33.3% lower. Axial strains at all reinforcement locations remain within the elastic range, confirming that concrete damage is governed by the low tensile capacity of concrete rather than reinforcement yielding.

Solids doi: 10.3390/solids7040037

Authors: Adán Ramírez-López Juan Alberto Alcántara-Cardenas Federico Chávez-Alcalá Ángel de Jesús Morales-Ramírez Héctor Herrera-Hernández

The new requirements for materials with improved properties and resistance to hazardous aggressive environments is very important in industrial incinerators and stoves. Thus, the present manuscript is dedicated to the study of the chemical interaction between Fe-Cr alloys at high temperatures (500–600 °C). Four alloys with different Al, Si, and Mo chemical composition were tested to determine their resistance to active laboratory conditions. The conditions were established based in those inside waste disposal incinerators. Laboratory equipment was set up to reproduce an enclosed aggressive but controlled atmosphere. Cylinders filled with N2 and O2 generated an 8% vol, and other containers produced a 220 vppm of HCl, 360 Vppm of H2O, and 200 vppm of SO2. The exposition was not continuous because the goal was to analyze the material response along different exposition times. The corrosion products that resulted after chemical etching were characterized using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and taking an average of various thermo-gravimetric measurements. The main products were Cr2O3, Fe2O3, Fe0.6Cr0.4, and Fe and Cr. The alloy with the best performance was found and theoretical principles of corrosion were analyzed to understand the corrosion mechanisms, which were driven by the formation of non-protective oxides.

Solids doi: 10.3390/solids7040036

Authors: Andrés González-Hernández Eugenio Rodríguez Edgar Onofre-Bustamante Willian Aperador Rodolfo Barragán-Ramírez Martín Flores-Martínez

Corrosion of carbon steel components represents a major economic and safety challenge in industrial applications, motivating the development of protective thin film coatings with optimized deposition parameters. This study investigates the deposition of nickel nitride (Ni-N) thin films on AISI 1016 carbon steel and silicon (111) wafers by reactive radio-frequency (r.f.) magnetron sputtering at three power levels: 150, 175, and 200 W. Surface color, film thickness, roughness, crystal structure, mechanical properties, and electrochemical behavior were evaluated using optical microscopy, stylus profilometry, atomic force microscopy (AFM), X-ray diffraction (XRD), nanoindentation, and potentiodynamic polarization combined with electrochemical impedance spectroscopy (EIS). Increasing r.f.-power produced systematic surface color changes consistent with variations in film thickness, which ranged from approximately 25.0 to 50.7 nm. Higher deposition power promoted smoother surfaces, with average roughness (Ra) decreasing from 64.28 nm at 150 W to 20.62 nm at 200 W. XRD analysis revealed a monocrystalline Ni3N hexagonal close-packed (HCP) phase at 150 W, transitioning to a dual-phase Ni3N (HCP) and Ni4N face-centered cubic (FCC) microstructure at 175 and 200 W. The highest hardness (11.80 ± 3.34 GPa) was recorded at 150 W, accompanied by pop-in events attributed to dislocation nucleation in the HCP lattice. Electrochemical evaluation in 3.5 wt.% NaCl solution demonstrated that films deposited at 150 and 175 W exhibited corrosion current densities and rates exceeding those of bare steel, confirming that these conditions accelerate rather than inhibit corrosion. Only the film deposited at 200 W achieved superior corrosion protection, with a corrosion current density and rate approximately 50% lower than bare steel, attributed to its denser microstructure and smoother surface morphology. These findings demonstrate that r.f. power is a critical parameter governing the properties of Ni-N thin films, and that careful optimization of deposition conditions is essential before recommending such coatings for industrial corrosion-protective applications.

Solids doi: 10.3390/solids7040035

Authors: Japneet Kukal Maria Soledad Peresin Armando G. McDonald

The study investigated the addition of nanocellulose (NC) as a reinforcing agent in wood-phenol resorcinol formaldehyde (PRF) composites for thermoset extrusion-based manufacturing. Three types of NC (cellulose nanocrystals (CNC), bleached nanofibers (BNFs), and unbleached nanofibers (UBNFs)) at 1–3% loadings and new (NP) and 4-year old (OP) PRF resin were evaluated by a combination of thermal analysis, rheology and flexural testing. The NP was shown to gel at a lower temperature than OP. CNC addition advanced gelation and yield stress; whereas, UBNFs reduced viscosity and yield stress through plasticization but were suitable for extrusion. The NC-reinforced wood–PRF formulations were successfully extruded into continuous composite rods. A flexural modulus of 8.1 GPa and strength of 77 MPa was achieved. Moreover, NC was shown to reduce 24 h water absorption compared to controls. These findings show that NC reinforcement improves wood–PRF composites systems for potential sustainable additive manufacturing.

Solids doi: 10.3390/solids7040034

Authors: Christina Papaspiropoulou Fotios I. Michos Nikos Aravantinos-Zafiris Michail M. Sigalas

In this work, the structural, optical, vibrational, and stability properties of a series of AlxAsx nanostructures are systematically investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Starting from the fundamental cubic-like Al4As4 building block, progressively larger nanostructures were constructed through directional elongation and structural rearrangements, allowing for the exploration of one-dimensional chains, two-dimensional planar structures, and several exotic geometries. The calculated UV–visible absorption spectra reveal that structural dimensionality and topology strongly influence the electronic transitions of the nanostructures, with elongated and distorted configurations exhibiting broader absorption features and richer spectral distribution. Vibrational analysis shows that increasing structural complexity and reducing symmetry lead to a higher density of IR-active modes and more complex infrared spectra. The stability of the nanostructures is evaluated through binding energy calculations, which indicate a clear size-dependent stabilization trend, with the Al24As24-L1 configuration exhibiting the highest stability among the examined systems. In addition, the calculated HOMO-LUMO gaps reveal the semiconducting character of the clusters and demonstrate their sensitivity to geometric topology. The present results establish clear structure–property relationships between dimensional growth and the optical response of AlAs nanoparticles and provide theoretical reference data for future experimental investigations of III-V semiconductor nanostructures.

Solids doi: 10.3390/solids7040033

Authors: Spyridon Mougkopetros Iosif Galanakis

The structural, electronic, and magnetic properties of the PdRSb, usually also referred to as RPdSb, (R= La-Lu) semi-Heusler compound series have been systematically investigated using first-principles calculations based on Density Functional Theory (DFT). Our structural optimizations reveal that the cubic C1b A-type variant is the energetically most favorable and thermodynamically stable ground state across the entire series. The calculated equilibrium lattice constants follow the well-known lanthanide contraction trend, with the exception of the Yb-based compound, which displays an anomalous lattice expansion. Magnetic stability analysis demonstrates that the magnetism is highly localized at the rare-earth (R) sites and closely follows the progressive filling of the 4f shell, peaking at 7μB for PdGdSb, while PdLaSb, PdYbSb, and PdLuSb remain non-magnetic. Furthermore, our electronic structure calculations reveal a rich variety of behaviors: PdLaSb and PdLuSb behave as gapless semiconductors, while most of the magnetic compounds exhibit near half-metallic characteristics. Notably, PdCeSb is predicted to be a perfect half-metal with an integer magnetic moment of 1μB. These findings highlight the significant chemical tunability of the PdRSb family, positioning them as promising candidates for future applications in spintronics and magnetoelectronics.

Solids doi: 10.3390/solids7030032

Authors: Annalaura Zilio Mattia Parnigotto Christian Durante Enrico Bernardo

The present study addresses the fabrication of porous gyroid architectures by additive manufacturing from preceramic polymer feedstocks. Photocurable emulsions were engineered by combining a silicone powder with acrylate monomers and dispersing an emulsified secondary phase of calcium nitrate. The formulations showed light-curing behaviour compatible with digital light processing vat photopolymerization (DLP-VPP), enabling high-fidelity replication of triply periodic minimal surface (TPMS) gyroids (designed porosity: 85 vol.%). After pyrolysis in nitrogen at 700 °C, the lattices converted into CaO–SiO2-derived amorphous matrices embedding an in situ turbostratic/pyrolytic carbon fraction, as suggested by the photothermal response and preliminary impedance behaviour, although the latter was measured in liquid electrolyte and therefore does not isolate electronic transport. To improve robustness during polymer-to-ceramic conversion, pharmaceutical borosilicate waste glass (BASG) was added as a passive filler (30–70 wt.%). The waste-glass phase acts as a passive filler that improves processing robustness and can mitigate shrinkage-induced damage during pyrolysis, while remaining electrically insulating (dielectric) and therefore not directly contributing to electronic conduction. The resulting structures combine high surface-to-volume ratio, controlled open porosity, and structural integrity with electrochemical responsiveness under the adopted test conditions, making them promising architected platforms for electrochemical components where interconnected porosity is advantageous.

Solids doi: 10.3390/solids7030031

Authors: Hao Yu Xiaowei Fan

Two-dimensional molybdenum disulfide (MoS2) has emerged as a promising candidate for next-generation electronics and optoelectronics; however, its scalable synthesis with precise control over domain size and film continuity remains challenging. Herein, we report a physical vapor deposition (PVD)-assisted chemical vapor deposition (CVD) strategy for the controllable growth of high-quality monolayer MoS2. By thermally evaporating an ultrathin (3 nm) MoO3 precursor film, spontaneous post-deposition dewetting yields a porous honeycomb morphology that significantly enhances vapor–solid reaction kinetics during subsequent sulfurization. Crucially, by modulating the argon carrier gas flow rate to regulate the local sulfur chemical potential, we achieve distinct growth regimes: a high flow rate (70 sccm) suppresses nucleation density, enabling isolated triangular and hexagonal single crystals with lateral dimensions up to 500 μm, whereas a reduced flow rate (50 sccm) promotes high-density nucleation and coalescence into continuous centimeter-scale polycrystalline films. Comprehensive structural and optical characterizations, including atomic force microscopy, Raman spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy, confirm that the synthesized MoS2 exhibits prototypical monolayer thickness (~0.7 nm), well-defined local crystallinity and a direct bandgap emission at 1.84 eV. This work establishes a robust, scalable, and highly tunable route for synthesizing large-area 2D TMDs tailored for advanced device integration.

Solids doi: 10.3390/solids7030030

Authors: Gennady Poletaev Alexander Semenov Yuriy Bebikhov Roman Rakitin

Using the molecular dynamics method, the compression of nickel nanoparticles with a nanocrystalline structure was simulated. The influence of the nanoparticle size (from 2 to 20 nm) and the average grain size within it (from 2 to 8 nm) on the compressive strength and on the strain at which the maximum stress is reached was investigated. In addition, the stability of the nanocrystalline structure of the nanoparticles was studied as a function of temperature and grain size. It is shown that the smaller the diameter of the nanocrystalline particle, the higher the compressive strength and the strain at which the maximum stress is reached. A decrease in grain size leads to a reduction in compressive strength, which is associated with the main mechanism of plastic deformation of nanocrystalline nanoparticles, namely, grain boundary sliding. At the first stage of deformation, the entire particle structure typically rotates until the maximum value of the stress vector projection onto the preferred slip plane is reached, which, in the case of a nanocrystalline structure, is determined by the mutual orientation of the grain boundaries. Grain boundaries elongated approximately along a single plane represent, in this case, the preferred slip plane.

Solids doi: 10.3390/solids7030029

Authors: Tatsuya Mori Miroslaw Maczka Seiji Kojima

KTaO3 (KTO) is a quantum paraelectric perovskite oxide which belongs to the cubic space group Pm3¯m in a large temperature range. Polar optical modes with a T1u symmetry of KTO are infrared-active and Raman-inactive according to the centrosymmetric exclusion principle of the selection rule. In general, the soft modes responsible for ferroelectric instability are infrared-active and Raman-inactive in the paraelectric phase. Therefore, there are still not enough studies on Raman-inactive soft modes and related phonon polaritons. In the present study, Raman-inactive polar modes and related polaritons of KTO crystals are studied by Terahertz Time-Domain spectroscopy (THz-TDS) and FTIR. The real and imaginary parts of a dielectric constant along the [100] axis are uniquely determined by transmission and reflection THz-TDS without any fitting in the low-frequency range between 6 and 225 cm−1, which covers the two lowest-frequency polar modes. The reflectivity is determined by reflection FTIR in the range between 50 and 1200 cm−1, and the complex dielectric constant is also estimated by the fitting in the range between 6 and 1200 cm−1. The phonon–polariton dispersion relations of the real and imaginary parts of the polariton wavevector are also studied in the range between 6 and 1200 cm−1. The crossover from photon-like to phonon-like polaritons and related polariton decay are observed, while no anomaly related to polariton scattering and coupling to other elementary excitations is observed in the polariton dispersion.

Solids doi: 10.3390/solids7030028

Authors: Linda Furlan Hamada Elsayed Enrico Bernardo

Polymer-derived ceramics (PDCs) technology has been established for over five decades as a versatile route for the fabrication of advanced bioceramic materials. However, conventional processing routes for bioceramics, such as melt-quenching and sol–gel methods, still present significant limitations, including high processing temperatures, limited compositional flexibility, long processing times, and difficulties in fabricating complex and highly porous structures required for biomedical applications. In this context, increasing attention has been devoted to polymer-derived ceramics as an alternative approach for the fabrication of bioceramic materials. In this approach, preceramic polymers are converted into ceramic phases through thermal treatment in air or inert atmosphere (e.g., nitrogen), enabling low-temperature processing, high compositional flexibility, and precise control over phase evolution and microstructure. These features make the polymer-derived Ceramic route particularly attractive for the fabrication of complex and functional bioceramic architectures. This review provides an overview of the polymeric precursors employed for the synthesis of Polymer Derived Ceramic-based bioceramics, with particular emphasis on inorganic polymers, typically characterized by a siloxanic backbone, and the mechanisms governing their ceramization behavior. Special attention is given to emerging trends, including the integration of polymer-derived ceramics with additive manufacturing techniques and the development of functional systems for biomedical applications.

Solids doi: 10.3390/solids7030027

Authors: Steffen Wilbrandt Olaf Stenzel

The determination of the linear optical constants of solids is an important part of solid state optical characterization. Reflection spectroscopy and ellipsometry of surfaces or thin solid films represent established techniques to access those optical constants; however, they may suffer from ambiguity in the obtained optical constants. We discuss methods for identifying the physically meaningful solution from the solution multiplicity, making use of a proper combination of independent measurements. Elaborating contours of constant reflectance (iso-reflectance curves) facilitates the reliable identification of correct optical constants. A numerical criterion is further provided to select suitable combinations of measurements. The procedure is demonstrated through its application to simulated spectra of a Nb2O5 film in the spectral region where the onset of the fundamental absorption edge is observed.

Solids doi: 10.3390/solids7030026

Authors: Chuanjin Wang Junshu Wu Jinshu Wang

The persistent accumulation of antibiotic pollutants in aquatic environments poses potential threats to ecological safety and human health, highlighting the importance of developing low-cost, high-performance adsorbents for their efficient removal. In this study, a hydrothermal method was employed to prepare highly dispersed coal gangue-based calcium silicate hydrate (CSH) adsorbents. The structural characteristics, adsorption performance, and adsorption mechanisms of the material were systematically investigated. The as-prepared CSH exhibited an interwoven nanorod/nanosheet composite morphology with a more developed pore structure and a higher specific surface area. Kinetic analysis indicated that the adsorption process followed a pseudo-second-order model and involved both Boyd diffusion and intraparticle diffusion, with liquid-film diffusion likely serving as the primary rate-limiting step. Isotherm analysis revealed that the adsorption behavior was well described by the Langmuir model, suggesting monolayer adsorption, with a theoretical adsorption capacity (Qm) of 129.29 mg/g. Thermodynamic analysis further demonstrated that the adsorption of CIP onto CSH was a spontaneous and endothermic process. Combined characterization results and theoretical calculations suggested that the adsorption of CIP by CSH was mainly governed by surface oxygen containing active sites, accompanied by electrostatic interactions, hydrogen bonding, and possible surface coordination effects. In addition, CSH maintained excellent adsorption performance and structural stability in the presence of coexisting ions, in tap water systems, and after repeated adsorption–desorption cycles. This study not only enables the high-value utilization of coal gangue but also provides new insights into the development of low-cost adsorbent materials for antibiotic removal.

Solids doi: 10.3390/solids7030025

Authors: Alexander A. Matvienko Andrey S. Skrypnik Pavel A. Gribov Ulanbek K. Mamytbekov Mustafa M. Kidibaev Anatoly A. Sidelnikov

This work presents a comprehensive investigation of the thermal decomposition of nickel oxalate dihydrate as a precursor for the synthesis of porous NiO, with particular emphasis on microstructural formation and evolution. The transformations occurring at successive stages of the reaction were examined using SEM, TEM, N2 adsorption, TG–DSC–MS, and in situ powder XRD, enabling the mechanisms of pore formation to be elucidated. The decomposition results in the formation of a porous pseudomorph composed of NiO nanoparticles with an average size of approximately 4 nm. This is the first time that the resulting microstructure has been shown to exhibit hierarchical, bimodal porous architecture. During dehydration, macropores are generated as a result of crystal fragmentation into blocks several hundred nanometers in size. Subsequent oxalate decomposition leads to the formation of mesoporous aggregates composed of nanometer-sized particles. The factors governing the parameters of the porous microstructure are analyzed. The resulting NiO, with its hierarchical pore structure, shows significant potential for applications in heterogeneous catalysis, gas sensing, and as electrodes for supercapacitors, lithium-ion batteries, and photoelectrochemical devices, as its macropores facilitate mass transport by reducing diffusion resistance while its mesopores provide a large accessible surface area for adsorption and catalytic reactions.

Solids doi: 10.3390/solids7030024

Authors: Marianne Mödlinger Alessia Provino Pavlo Solokha Serena De Negri Antonio Bianco Cristina Bernini Pietro Manfrinetti

An experimental investigation of the Cu-As-Sb ternary system in the Cu-rich region led to the identification of a new intermetallic phase, Cu5(As,Sb)2. The compound crystallizes in the orthorhombic Mg5Ga2-type structure (oI28, Ibam), analogous to the binary parent phase Cu5As2, with lattice parameters a = 5.968–5.977(1) Å, b = 11.550–11.565(3) Å, c = 5.530–5.573(3) Å. Similar to the parent Cu5As2 phase, the ternary compound forms with slight Cu under stoichiometry and exhibits a limited compositional range, with no continuous solid solubility between the binary and ternary phases. The phase formation, compositional stability, and decomposition behavior were systematically studied using a combination of powder and single-crystal X-ray diffraction (XRD, including Rietveld refinement), metallographic analysis with optical and scanning electron microscopy with energy-dispersive X-ray spectroscopy (LOM, SEM-EDXS), electron backscatter diffraction (EBSD) and thermal analysis (DTA, DSC). The results reveal that Cu5(As,Sb)2 is a high-temperature phase forming peritectically at 650–635 °C and stable only within a limited temperature interval. No continuous solid solubility exists between the ternary compound and the parent binary phase Cu5As2. Its formation occurs in strong competition with that of two other close neighboring solid-solution compounds, [Cu3−x(As1−ySby) (Cu3P-type; hP24, P63cm) and Cu3−x(As,Sb) (Cu9TeSb2-type; cP32, Pm−3n)], reflecting a complex interplay between composition, solubility ranges and thermal history. No evidence for the existence of high-temperature (HT) and low-temperature (LT) polymorphic phases was found for either the binary compound Cu5As2 or the ternary compound Cu5(As,Sb)2. Electrical resistivity measurements on a quenched sample indicate metallic behavior. These findings provide new insight into phase stability and structure–property relationships in Cu-As-Sb alloys and contribute to the understanding of competing intermetallic phases in this system.

Solids doi: 10.3390/solids7030023

Authors: Xiaonan Hu Fangpei Li Guohe Zhang Yongning He Wenbo Peng

Piezoelectric semiconductor combines the unique properties of semiconducting characteristics and piezoelectric effect together, providing a universal methodology to modulate piezoelectric semiconductor device’s performance by simply introducing mechanical strain. To reveal the device physics beneath the piezoelectric modulation, in this work, a multiphysics COMSOL 6.0 simulation was employed to investigate the modulation of Si/GaN heterojunction PN diode characteristics via piezoelectric-induced interface polarization charges. The effects of charge polarity and density on forward recovery, reverse recovery, and irradiation responses were systematically analyzed. The results demonstrate that negative interface charges enhance carrier injection and accelerate device activation, whereas positive charges suppress overshoot and stabilize transient voltage behavior. During reverse recovery, negative charges shorten the storage delay and reduce the reverse peak current, improving the switching speed, whereas positive charges cause slower recovery. Under irradiation, the interface polarization charges modulate the photocurrent density by altering the depletion width and carrier collection efficiency; negative charges notably enhance the photocurrent in partially depleted devices. Furthermore, the influence of the polarization charges diminishes with increasing device length or doping concentration, as the built-in charge and electric field effects dominate. This study elucidates the physical mechanisms of piezoelectric charge control in Si/GaN heterojunctions and provides theoretical guidance for the design of high-speed, low-loss, and radiation-tunable power and optoelectronic devices.

Solids doi: 10.3390/solids7020022

Authors: Om Prakash Gujela Mario Hofmann Ding-Rui Chen

Two-dimensional (2D) heterostructures offer tunable electronic structures and synergistic interactions that enhance electrocatalytic activity beyond the limits of single-component materials. However, the same atomically thin interfaces that enable high performance also introduce inherent mechanical, chemical, and electronic vulnerabilities, giving rise to complex and coupled degradation pathways. In this review, we provide a systematic overview of degradation in 2D heterojunction electrocatalysts during electrochemical operation, covering failure mechanisms, operando characterization, and stabilization strategies. Degradation is governed by interfacial strain accumulation, bubble-induced stress and delamination, galvanic corrosion, and selective leaching, while stability can be improved through interfacial coupling, structural confinement, and controlled reconstruction. These insights provide practical design guidelines for developing robust 2D heterostructures for electrochemical energy conversion.

Solids doi: 10.3390/solids7020021

Authors: Tae Hun Kim Seung Gun Kim Jongyun Choi Ji Chul Jung Jung-Chul An Patrick Joohyun Kim Dalsu Choi Inchan Yang

Plastic pyrolysis is widely used to treat polyolefin-rich waste; however, wax byproducts generated during these processes are typically regarded as low-value intermediates. Here, a byproduct-compatible upcycling strategy is proposed to convert polyethylene (PE) pyrolysis wax into activated carbon, enabling integration of functional carbon production into existing recycling value chains. Thermal oxidation was employed to stabilize the wax prior to carbonization, and stabilization at 300 °C yielded a mechanically stable precursor with a high carbon yield. Subsequent carbonization and KOH activation at 900 °C produced an activated carbon (PEWax_AC) with a specific surface area of 1704 m2/g, exceeding that of a representative commercial activated carbon (1575 m2/g). Microstructural analysis revealed predominantly amorphous carbon with locally ordered domains. In symmetric supercapacitor cells, PEWax_AC exhibited higher capacitance at low rates and superior rate capability at high scan rates and current densities, along with reduced charge-transfer resistance. Specifically, PEWax_AC delivered a specific capacitance of 22.9 F/g at 5 mV/s and exhibited a rate retention of 18.6% from 0.1 to 7.0 A/g. These findings demonstrate that plastic pyrolysis wax is a viable and scalable carbon precursor for high-performance supercapacitor electrodes.

Solids doi: 10.3390/solids7020020

Authors: K. Arun Joshi Reddy Subhendu Jana Sweta Yadav Paul A. Maggard

Metal-chalcogenide compounds with perovskite-type compositions have drawn increasing attention for their optical properties for solar energy conversion. Herein, a new α-type polymorph of the ternary sulfide SrHfS3 is described, crystallizing in the NH4CdCl3 structure type. The yellow-colored plate-shaped crystals were synthesized at 1173 K using an elemental tin flux in an evacuated sealed tube. Its crystal structure was characterized at room temperature using single crystal X-ray diffraction to form in the orthorhombic Pnma space group, with the refined cell parameters of a = 8.5041(4) Å, b = 3.8004(2) Å, c = 13.8935(6) Å, and V = 449.02(4) Å3. The structure comprises five independent crystallographic sites, having one Sr, one Hf, and three S sites. The structure can be described as containing one-dimensional chains of distorted HfS6 octahedra extending down the b-axis to form 1∞[HfS3]2− strips of edge-sharing octahedra. The Sr atoms act as charge-balancing space fillers in the structure. High-purity bulk samples of α-SrHfS3 could be prepared for measurement of its bandgap by optical diffuse-reflectance spectroscopy, showing a direct bandgap of 2.1(1) eV. Results of electronic structure calculations are consistent with this bandgap and type. The conduction and valence band edges stem from the respective empty Hf d-orbitals and the filled S p-orbital states. In summary, crystal growth of the α-type polymorph of SrHfS3 has been demonstrated using a Sn flux approach, which can facilitate future broader synthetic explorations at lower temperatures.

Solids doi: 10.3390/solids7020019

Authors: Daniel Cristișor Corneliu Munteanu Daniela-Lucia Chicet Marcelin Benchea Alina-Corina Dumitrașcu Adi-Mihăiță Velniciuc

Cr2O3-based ceramic coatings are widely used in wear-critical applications; however, their tribological performance under dry sliding conditions can be limited by brittleness and frictional instability. In heavy-duty vehicles, the king pin–bushing contact operates under severe dry sliding conditions, motivating the investigation of composite Cr2O3–nTiO2 coatings as a potential surface engineering solution. In this study, Cr2O3–TiO2 coatings containing 0, 10, 20, 30, and 40 wt% TiO2 were deposited by atmospheric plasma spraying (APS) from mechanically mixed powders. Phase composition was analyzed by X-ray diffraction using an X’Pert PRO MRD diffractometer, while microstructure and elemental distribution were examined by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) on a FEG Quattro C microscope. Mechanical properties were evaluated by Vickers microhardness, instrumented indentation and scratch testing, while dry sliding wear behavior was assessed by pin-on-disc tests performed on a CETR UMT-2 tribometer against a bronze counterbody, with continuous monitoring of the coefficient of friction (COF). The results show that plasma spraying produces lamellar composite coatings with intrinsic porosity and locally modified phase composition. Cr2O3-rich coatings exhibit higher hardness (1198 HV2 compared with 877 HV2 for Cr2O3–40TiO2 corresponding to an increase of approximately 36%) and improved resistance to indentation, reflected by lower penetration depths and higher elastic modulus values (134 GPa for S0 compared with 77 GPa for S2). These coatings also exhibit a more stable friction response and reduced material transfer from the bronze counterbody, as confirmed by the lower mass loss of the pins (0.0295 g for S0 compared with 0.0473 g for S4, corresponding to a reduction of about 38%). Increasing TiO2 content leads to changes in friction stability and wear behavior associated with microstructural heterogeneity. These findings indicate that the sliding wear performance of Cr2O3–nTiO2 coatings is governed by elastic–plastic stability under localized contact loading and support their applicability for dry sliding king pin–bushing systems in heavy-duty vehicles.

Solids doi: 10.3390/solids7020018

Authors: Mingqi Gao Dongyang Lei Yagang Zhang Huijie Ye Yanming Zhang Ce Zeng Tong Hu Hai Jiang Qian Lu Yueyou Yang An Zhang

A ceramic-packaged, dual-layer-stacked System-in-Package (SiP) architecture combines the hermeticity of ceramic substrates with the superior radio frequency (RF) performance of organic substrates to meet the demands for high-density integration, cost-effectiveness, and high performance. This study investigates the issues of thermal mismatch, solder joint contamination, and void formation during the large-area eutectic bonding of the lower organic substrate using Pb70In30 solder through simulation and an experimental approach. The results indicate that: (a) the post-bonding warpage of the organic substrate can be reduced to under 80 µm by optimizing its copper layer thickness, dielectric layer thickness, and cavity/slot distribution, and (b) flux pretreatment can be employed to reduce the Pb70In30 solder in an N2/H2 mixture at a eutectic temperature of 285 °C and a pressure of 1.5 kPa effectively promotes solder spreading, prevents solder joint contamination, and yields a void formation percentage below 10%, a shear strength of 23.66 MPa, and solder overflow exceeding 90%, thereby satisfying the requirements for reliable large-area eutectic bonding. These findings offer guidance for the packaging process design of ceramic-packaged, dual-layer-stacked SiPs.

Solids doi: 10.3390/solids7020017

Authors: Francesco Branda Rossella Grappa Dario De Fazio Luca Boccarusso Massimo Durante Giuseppina Luciani

The recycling of carbon fiber-reinforced polymers (CFRPs), particularly carbon fiber-reinforced epoxy polymers (CFREPs), is a challenging problem because of their broad application spectrum, the amount of laminates produced per year, and the cost per kg of the carbon fiber fabric. Recently, several papers were published on the recycling of CFREPs through solvothermal methods that allow the recovery of the carbon fiber fabrics with a relatively low environmental impact. In the present paper, for the first time, the effect of the presence of flame retardants is discussed. A carbon fiber-reinforced epoxy polymer (CFREP) charged with P-, Zn-, B- and Al-based flame retardants, supplied by the aerospace industry, was subjected to a double-step solvothermal treatment. The epoxy matrix was successfully dissolved in monoethanolammine after a preswelling step in acetic acid. The experimental results show that the proposed process allows the full recovery of the carbon fabric with its original sizing layer without injury to the fiber. As confirmation, CFREP laminates produced with the recycled carbon fiber fabrics exhibited mechanical properties close to that of laminates obtained from the virgin epoxy/carbon prepreg. Contrary to what is reported in the literature, the present paper also shows that, in the studied case, whilst acetic acid treatment promotes swelling, it also causes the formation of a degraded surface layer that would impede complete removal of the polymeric matrix and full recovery of the carbon fabric if only acetic acid was used. On the basis of the known mechanism of flame retardancy of phosphates and borates, the degraded layer formation is attributed to the acidic character of the acetic acid. It is worth pointing out that the paper suggests, therefore, that the presence of flame retardants may strongly affect the solvothermal processes.

Solids doi: 10.3390/solids7020016

Authors: Mohamed Bejaoui Mahdi Meftah Walid Oueslati

Poly(vinyl alcohol) (PVA)/montmorillonite (MMT)/Ti3C2Tx (MXene) nanocomposite membranes (PVA/MMT/MXene) were developed and evaluated in terms of their mechanical properties, mesoporosity, and adsorption performance toward Pb2+ ions and methylene blue (MB). The incorporation of MMT and MXene resulted in a strong synergistic reinforcement, increasing the ultimate tensile strength from 10 to 20 MPa, the Young’s modulus from 14.7 to 29.5 MPa, and reducing the swelling ratio from 2.0 to 1.1 g·g−1. BJH porosimetry revealed a refined and interconnected mesoporous structure, with the cumulative pore volume increasing from 0.134 to 0.448 cm3·g−1. In adsorption experiments (mono-solute systems, 25 °C), the ternary membrane achieved high uptake capacities of 55 mg·g−1 for Pb2+ and 80 mg·g−1 for MB, outperforming binary PVA/MMT and neat PVA. Statistical–physics modeling provided microscopic descriptors consistent with the experimental isotherms: Pb2+ adsorption follows a monolayer regime (n ≈ 1), whereas MB exhibits multilayer behavior (n > 1) with a higher site density (Nm ≈ 1.6 mmol·g−1). These results demonstrate that the hybrid 2D–2D architecture of MMT and MXene significantly enhances the structural robustness, pore accessibility, and adsorption efficiency of PVA-based membranes, highlighting their potential for efficient removal of metal ions and dyes from aqueous media.

Solids doi: 10.3390/solids7020015

Authors: Andrey V. Poligenko Evgeny A. Ruban Kirill M. Osipov Andrey A. Shaporenkov Vladimir V. Dushik

This review systematizes data on the phase composition and key properties of compounds in the W–B system, including thermodynamic stability, crystal structure, and hardness. The current understanding of the binary W–B phase diagram and the stability of individual borides is discussed, alongside the influence of defects and non-stoichiometry on their properties. The main methods for synthesizing these materials and producing coatings based on them are summarized. Potential applications of tungsten borides are highlighted, particularly for high-temperature environments, cutting tools, and protective and functional coatings. Finally, key directions for future research are outlined, focusing on the refinement of phase equilibria, the scaling of production methods, and the development of W–B-based materials with tailored performance characteristics.

Solids doi: 10.3390/solids7020014

Authors: Ufana Riaz Selina Arrington-Boyd Rajeev Kumar Darlene K. Taylor

Enhancing the solubility and processability of graphene remains a critical challenge, limiting its integration into advanced materials systems. In this work, poly(tert-butyl acrylate) (PtBA) and poly(N-isopropyl acrylamide) (PNIPAM) were grafted onto graphene via controlled atom transfer radical polymerization (ATRP) to create well-defined polymer–graphene hybrids with tunable interfacial properties. ATRP enabled the synthesis of PtBA and PNIPAM homopolymers with narrow molecular weight distributions and systematically varied chain lengths (4–18 kDa), allowing direct correlation between polymer architecture and material performance. Notably, the thermos-responsive behavior of PNIPAM was strongly dependent on chain length, highlighting the importance of controlled polymer design. Raman and FTIR spectroscopy confirmed successful grafting and chemical modification of the graphene surface. In addition, pilot studies demonstrate the ATRP synthesis of PtBA-b-PNIPAM block copolymers and their hydrolysis to PAA-b-PNIPAM, providing a platform for future development of multifunctional graphene interfaces. Overall, this study establishes a versatile and precisely controlled route for engineering polymer-grafted graphene with enhanced solubility and tunable functionality, enabling broader applications in smart materials and hybrid nanocomposites.

Solids doi: 10.3390/solids7020013

Authors: Yoshihiko Hangai Kentaro Ishiuchi Kenji Amagai Nobuhiro Yoshikawa

Aluminum foam is expected to be applied in various industrial fields as a lightweight, multifunctional material. When it is used as an industrial product, it is essential to form it into the required shape. There have been some attempts to form aluminum foam. However, the formability remains low. In this study, we attempted to form aluminum foam, which was fabricated by heat foaming a precursor, into a flat plate by reheating it above its foaming temperature and then roller forming it. It was found that heating above the foaming temperature and subsequent roller forming enabled the aluminum foam to be formed into a flat plate without causing defects. In a sample in which the precursor was roller-formed immediately after foaming, it was found that compared to the as-foamed aluminum foam, the decrease in porosity was limited to approximately 5%, enabling roller forming while minimizing the influences on pore structures. In samples that were roller-formed after reheating, porosities slightly decreased, but most pores were retained. Even when the aluminum foam was roller-formed to the same thickness as the initial precursor before foaming, the porosities exhibited around 65%, limiting the reduction in porosities to approximately 15% compared to the as-foamed aluminum foam.

Solids doi: 10.3390/solids7010012

Authors: L. P. Rivera César D. Rivera-Tello J. G. Quiñones-Galván

Tin oxide thin films were deposited by the pulsed laser ablation of a metallic Sn target at different oxygen partial pressures, ranging from 10 to 40 mTorr. Langmuir plasma probe diagnostics were performed to evaluate the effect of pressure on mean kinetic energy and density of Sn ions. It was observed that the mean kinetic energy decreased from 34 to 11 eV while the ion density decreased from 10 to 1.5 × 1013 cm−3 with increasing pressure. The films exhibited enhanced optical transmittance, increasing from 10% for the sample grown at 10 mTorr to 70% for the film deposited at 40 mTorr. Furthermore, higher deposition pressures led to wider band gap values, increasing from 1.6 to 3.9 eV for direct transitions and from 2.2 to 3.2 eV for indirect transitions with increasing oxygen pressure. These trends are consistent with progressive oxidation and partial transparency characteristic of semiconducting tin oxides. Structural characterization, based on X-ray diffraction, revealed predominantly metallic Sn diffraction peaks across the entire oxygen pressure range. However, despite this structural signature, the films exhibited optical and electronic properties characteristic of tin oxides. This apparent discrepancy suggests the coexistence of metallic nanoparticles embedded within an amorphous or nanocrystalline SnO2/SnOx matrix. These findings provide insights into the non-equilibrium oxidation dynamics of tin and the formation of metastable SnOx phases during pulsed laser deposition.

Solids doi: 10.3390/solids7010011

Authors: Mehmet Erdem Iris Metin Tanoglu Elmas Salamci Serkan Dehneliler Hande Iplikci Gozde Esenoglu

Adhesive bonding has emerged as a promising technology for joining carbon fiber reinforced polymer (CFRP) structures in aircraft, offering advantages over traditional mechanical fastening such as weight reduction and uniform stress distribution. This study evaluates the effectiveness of innovative laser ablation and electrospinning surface treatments compared to the conventional peel-ply method for secondary bonding. Surface features and wetting behavior were characterized using scanning electron microscopy (SEM) and contact angle measurements, while mechanical performance was assessed via single lap shear tests. Results demonstrate that laser ablation (30 W power, 10 m/s speed) achieved the highest bond strength at 20.68 MPa, followed by electrospinning (18.20 MPa) using 10 wt% PA-66 nanofibers. Both advanced techniques significantly outperformed the peel-ply method, which yielded the lowest shear strength of 15.18 MPa. SEM analysis confirmed that laser treatment facilitated direct fiber exposure with minimal damage, while nanofibers provided enhanced physical interlocking. In conclusion, laser ablation proved to be the most effective technique for enhancing interfacial bonding in aerospace-grade CFRP structures, followed by electrospinning, offering a superior alternative to traditional surface preparation.

Solids doi: 10.3390/solids7010010

Authors: Patrick Cleary Rhys Northcote Advaith Narayanan Miguel A. Quiñones Dean Kanelos Eric McCarty Cliff Butcher

The VDA 238-100 tight radius bend test has gained widespread acceptance for plane strain fracture characterization of sheet metals in proportional loading without necking. The VDA test features a 60 × 60 mm2 square blank with a 0.2 mm or 0.4 mm radius punch to provide plane strain bending where the fracture limit of the material is lowest. However, the through-thickness gradients that suppress necking and promote fracture on the convex surface in tension can be exploited to efficiently characterize the fracture strain from uniaxial to plane strain tension by varying the sample width. In this study, V-bend tests were conducted for various sample widths for four advanced high-strength steels: 980GEN3, DP1180, MP800-V1, and MP800-V2 with the local fracture strains measured using digital image correlation. Reducing the width-to-thickness ratio below five altered the stress state at the failure location, with an aspect ratio of one providing edge fractures under uniaxial tension. This aspect ratio was then applied to 980GEN3 and MP800 steel samples with punched edges as it provides an efficient method for sheared edge fracture characterization that is not susceptible to necking as with common sheared edge tensile tests. To mitigate strain averaging inherent in DIC near surfaces, a geometric-based arc length methodology was proposed. The sheared edge fracture limits from the V-bend tests were then compared with the results from conical hole expansion and in-plane bend tests. The sheared edge formability was observed to have a material-dependent sensitivity to the test method. MP800-V2, with centerline segregation, exhibited a pronounced sensitivity to the applied deformation mode with absolute differences in fracture strains of 0.13 while the MP800-V1 and 980GEN3 did not.

Solids doi: 10.3390/solids7010009

Authors: Syuan Chen Ming-Thau Sheu Chie-Shaan Su

This study developed a sonoseeding strategy for controlling the crystal size of acetaminophen during cooling crystallization by introducing sonication into a supersaturated solution, thereby inducing nucleation. Based on the synthetic route of acetaminophen, crystallization behavior in both water and acetic acid aqueous solutions was investigated, along with the influence of a structurally related additive, p-aminophenol, on nucleation. To establish the sonoseeding approach, the solubility of acetaminophen in water and an aqueous solution of acetic acid, with and without the additive, was measured over a temperature range of 10–70 °C using a titration method. In parallel, the nucleation temperatures and metastable zone widths of acetaminophen were systematically determined during cooling crystallization under varying operating conditions. Results demonstrate that sonication effectively induces nucleation and significantly narrows the metastable zone width, particularly in aqueous solutions of acetic acid. Guided by the determined solubility and nucleation behavior, sonoseeding crystallization experiments were conducted at various supersaturation levels, allowing for the efficient control of acetaminophen crystal size, which ranged from 27 μm to 95 μm, with narrower particle size distributions compared to spontaneous nucleation. Furthermore, the recrystallized acetaminophen was confirmed as Form I using PXRD, DSC, and FTIR analysis. This study demonstrates that the sonoseeding approach is an efficient method for controlling crystal size during the crystallization of active pharmaceutical ingredients.

Solids doi: 10.3390/solids7010008

Authors: Giacomo Canale Vitantonio Esperto Felice Rubino

Ceramic Matrix Composites (CMCs) have emerged as a structural material alternative to nickel superalloys for high-pressure turbines (HPT) components operating at high temperature, like shrouds. Despite the outstanding thermal stability of the CMCs, limited cooling is still necessary due to the extreme thermal operating conditions necessary to maximize engine performance and minimize fuel consumption. The design of CMC components, indeed, must consider a maximum service temperature that should not be exceeded to avoid damage and accelerated oxidation. The cooling, on the other hand, may induce the formation of thermal gradients and thermal stresses. In this work, different design options for the cooling system are investigated to minimize the thermal stresses of an HPT shroud-like geometry subjected to maximum temperature constraints on the material. Cooling is obtained via colder air jet streams (air taken from the compressor), whose impact position (the surface where the cold air impacts the component) has a different effect on the temperature field and on the induced stress field. Besides stress evaluation with different cooling systems, an ONERA damage model is investigated at a key location to potentially take into account stress components acting simultaneously and potential stiffness degradation of the CMC. Finally, the design evaluation of potential discrete crack propagation is discussed. A standard cohesive elements approach has been compared with a brittle element death approach. The results showed that the cohesive element approach resulted in shorter crack propagation, underestimating the actual crack behavior due to the embedded stiffness degradation method, while the element death returned encouraging results as a quicker, less complex, but still accurate design evaluation.

Solids doi: 10.3390/solids7010007

Authors: Hassan O. Shoyiga Msimelelo Siswana

Magnesium–sulfur (Mg-S) batteries represent a novel category of multivalent energy storage systems, characterised by enhanced theoretical energy density, material availability, and ecological compatibility. Notwithstanding these benefits, the practical implementation of this approach continues to be hindered by ongoing issues, such as polysulfide shuttle effects, slow Mg2+ transport, and significant interfacial instability. This study emphasises recent progress in utilising transition metal chalcogenides (TMCs) as cathode materials and modifiers to overcome these challenges. We assess the structural, electrical, and catalytic characteristics of TMCs such as MoS2, CoSe2, WS2, and TiS2, highlighting their contributions to improving redox kinetics, retaining polysulfides, and enabling reversible Mg2+ intercalation. The review synthesises results from experimental and theoretical studies to offer a thorough comprehension of structure–function interactions. Particular emphasis is placed on morphological engineering, modulation of electronic conductivity, and techniques for surface functionalisation. Furthermore, we examine insights from density functional theory (DFT) simulations that corroborate the observed enhancements in electrochemical performance and offer predictive direction for material optimisation. This paper delineates nascent opportunities in Artificial Intelligence (AI)-enhanced materials discovery and hybrid system design, proposing future trajectories to realise the potential of TMC-based Mg-S battery systems fully.

Solids doi: 10.3390/solids7010006

Authors: Li-Dong Wan Yan-Chun Li Dong-Ming Song Xue-Hai Ju

During long-term storage, polymer-bonded explosives (PBXs) undergo thermal-oxidative aging due to environmental factors such as moisture and oxygen, which leads to a critical determinant of explosive performance. This study employed molecular dynamics simulations to investigate the impact of thermal-oxidative aging of butadiene rubber and paraffin wax composites used in the RDX-based polymer-bonded explosives. The interfacial binding energy between the binder system and RDX crystalline surfaces was evaluated. The cohesive energy density (CED), fractional free volume (FFV), mean square displacement (MSD), and mechanical properties were analysed to probe the mechanism of aging for butadiene rubber (BR) and paraffin wax (PW). The results demonstrate that, with progressive aging, the oxidation-induced chain scission of BR molecules leads to an increase in both the CED and solubility parameter of the BR/PW system. Initial oxidation reduces the FFV of the BR/PW system from 0.183 to 0.166, while subsequent chain scission causes the FFV to rise to 0.175. In terms of mechanical properties, the BR/PW system exhibits ductile behavior, with reductions in both Young’s modulus and shear modulus as aging progresses, leading to decreased material stiffness. For the RDX/binder system, oxidation enhances the interfacial binding energy, whereas chain scission in BR leads to a slight decline in the binding energy. Overall, oxidation exerts a more pronounced influence on the interfacial binding energy compared to chain scission.

Solids doi: 10.3390/solids7010005

Authors: Donghua Xu Tittaya Thaiyanurak Noushin Salsabil

Atomic-scale strain is the basis of a material’s macroscopic deformation behavior. The current measure of atomic-scale strain in the form of the Green–Lagrange tensor loses its physical meaning beyond the yield point, as atomic neighborhoods undergo significant reconstructions. We have recently introduced a new atomic-scale strain measure, namely, atomic bond strain, through our study of bond behavior in multicomponent metallic glasses. Here, we apply this new strain measure to uniaxial tensile tests (simulated using molecular dynamics) of several representative single-crystal FCC (face-centered cubic) metals under varied strain rates. We show that this new strain measure displays remarkable near-linear correlation with stress, not only in the elastic regime, but also in the plastic regime where complex dislocation dynamics (nucleation, bursting, motion, annihilation, regeneration) and stress fluctuations take place. This suggests that the overall stress of the materials even in the plastic regime is predominantly determined by the degree of bond stretching among all atoms. This appears to contradict the common conceptions that the plastic flow stress of a crystalline material is governed by dislocation events involving only a small fraction of atoms around dislocations, and that the stress–strain relationship is highly non-linear for plastic deformation. The contradictions can be reconciled by considering the causal sequence: dislocation events alter bond stretching, and bond stretching directly determines the stress. This brings a novel insight into the nature of plastic deformation, owing to the newly introduced atomic bond strain. How well the near-linear correlation between the stress and the atomic bond strain holds in other materials (e.g., non-FCC single crystals, polycrystals, quasicrystals, elements, alloys, and compounds) is an intriguing and important topic for future investigation, following the example of this work.

Solids doi: 10.3390/solids7010004

Authors: Tung-Yuan Yung Yi-Ching Huang Kuan-Yi Lee Chun-Min Wu Wen-Hsien Li

A spiral spin arrangement with a magnetic unit cell 28 times the size of the nuclear one has been reported for Fe spins below TN = 80 K in bilayered van der Waals gapped FeOCl. In this work, we employ neutron magnetic diffraction and ac magnetic susceptibility to reveal a much smaller magnetic unit cell only 4 times the size of the nuclear one for Fe spins below TN = 119 K, upon intercalation of 27% non-magnetic Na ions into the van der Waals gaps of FeOCl. X-ray emission spectra and X-ray absorption edge spectra reveal a charge transfer from the intercalated Na ions to the Fe sites, which partially reduces the Fe3+ into Fe2+ ions. The reduction results in a significantly increased Fe-O-Fe bond angle, which strongly enhances the antiferromagnetic superexchange (AFMSE) coupling relative to the competing ferromagnetic direct exchange (FMDE) coupling between neighboring Fe ions, thereby driving to a higher degree of magnetic symmetry and a substantially higher Neel temperature for the Fe spins in Na0.27FeOCl.

Solids doi: 10.3390/solids7010003

Authors: Juan Alberto Alcántara-Cárdenas Adán Ramírez-López José Federico Chávez-Alcalá Manuel Macias-Hernández Ángel de Jesús Morales Ramírez

Understanding the corrosion mechanism inside waste incinerators is very important in order to prevent possible damage due to high operational temperatures in chemical reactions for burning raw hazardous materials. Moreover, it is critical to understand the corrosion mechanisms to identify whether the oxides formed are protective or not, enabling us to prevent mass change on the steel walls of heat exchangers in waste incinerators. Thus, the present work comprises a high-temperature corrosion study on four Ferritic alloys with different contents of Al, Si, and Mo which are capable of replacing expensive materials such as stainless steel. The corrosion behavior was evaluated in atmospheres with H2O(g), HCl(g), and an additional mixture of both atmospheres at 500 and 600 °C over 300 h. A thicker but porous heterogeneous oxide scale was formed in the HCl atmosphere, mainly composed of Fe2O3 and Cr2O3. Under the water vapor atmosphere, the presence of (Fe0.6Cr0.4)2O3 was observed. Meanwhile, in the mixed atmosphere, the presence of FeCr2O4, Cr2SiO4, and (CrFe)2O3 was observed. The biggest mass loss was measured inside the water vapor atmosphere. In comparison, inside the mixed atmosphere, the oxide scale was thinner. Finally, it was concluded that the alloy with the best corrosion resistance in HCl and H2O atmospheres was Fe9Cr1.5AlSi3Mo steel.

Solids doi: 10.3390/solids7010002

Authors: Yacob Ben-Aryeh

Intrinsic optical bi-stability in dense two-level systems is developed for the bad cavity limit where electromagnetic modes are adiabatically eliminated. Each atom interacts via dipole–dipole forces with its nearby spatial distribution of atoms. The theory is developed into two parts, corresponding to the short sample, with dimensions shorter than the wavelength, and the long sample. In both cases, the local field corrections modify the Maxwell–Bloch equations, so that cubic or quartic equations are obtained for the inversion of population as a function of the external light intensity, thus leading to intrinsic bi-stability. The effects of noise sources on intrinsic bi-stability were treated, and I found that while the observability of bi-stability was not obtained experimentally for a simple two-level system, there were many observations of bi-stability obtained through the ‘up-conversion’ of rare earth excited crystals. I show the differences between these two systems.

Solids doi: 10.3390/solids7010001

Authors: Giulio Siciliano Bridgette Sims Thomas Burns Wout De Backer Paul Ziehl Ralph White Paul Coman

Sodium-ion batteries (SIBs) present a sustainable alternative to lithium-ion systems due to the abundance and low environmental impact of sodium. However, their integration into multifunctional structural battery systems that combine electrochemical and mechanical properties remains unexplored. This work investigates the electrochemical performance of sodium-ion chemistry within a structural battery framework using unsized carbon fiber (UCF) as both a structural substrate and active electrode material. Ultrasonic spray coating was employed to deposit Mesocarbon Microbeads (MCMB) and NaNi1/3Fe1/3Mn1/3O2 (NFM) on UCF to form hybrid anode and cathode half-cells, respectively, with 1 M NaPF6 in diglyme electrolyte. The MCMB on UCF hybrid anode demonstrated dual graphitic and carbon fiber storage mechanisms, achieving 50 mAh g−1 capacity over 500 cycles at 1C with excellent Coulombic efficiency. The NFM–UCF cathode exhibited an initial capacity of 27.5 mAh g−1 and maintained over 80% capacity retention for 230 cycles, continuing to cycle stably beyond 400 cycles. Post-cycling SEM imaging revealed surface cracking, particle expansion, and gas-pocket formation in both electrodes. These results demonstrate the electrochemical viability of sodium-ion chemistry in a multifunctional structural configuration and establish ultrasonic coating as a scalable, precise method for fabricating carbon fiber electrodes toward future sodium-ion structural batteries.

Solids doi: 10.3390/solids6040069

Authors: Jude N. Ike Raymond Tichaona Taziwa

Thin-film organic solar cells (TFOSCs) are gaining momentum as next-generation photovoltaic technologies due to their lightweight nature, mechanical flexibility, and low cost-effective fabrication. In this pioneering study, we report for the first time the incorporation of cobalt-doped zinc sulfide (ZnS/Co) nanoparticles (NPs) into a poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) bulk-heterojunction photoactive layer. ZnS/Co NPs were successfully synthesized via a wet chemical method and integrated at varying concentrations (1%wt, 3%wt, and 5%wt) to systematically investigate their influence on device performance. The optimal doping concentration of 3%wt yielded a remarkable power conversion efficiency (PCE) of 4.76%, representing a 102% enhancement over the pristine reference device (2.35%) under ambient laboratory conditions. The observed positive trend is attributed to the localized surface plasmon resonance (LSPR) effect and near-field optical enhancement induced by the presence of ZnS/Co NPs in the active layer, thereby increasing light-harvesting capability and exciton dissociation. Comprehensive morphological and optical characterizations using high-resolution scanning electron microscopy (HRSEM), high-resolution transmission electron microscopy (HRTEM), and spectroscopic techniques confirmed uniform nanoparticle dispersion, nanoscale crystallinity, and effective light absorption. These findings highlight the functional role of ZnS/Co NPs as dopants in enhancing TFOSC performance, providing valuable insights into optimizing nanoparticle concentration. This work offers a scalable and impactful strategy for advancing high-efficiency, flexible, and wearable organic photovoltaic devices.

Solids doi: 10.3390/solids6040068

Authors: Vadim F. Agekyan Nikolai G. Filosofov Alexey Yu. Serov Igor V. Shtrom

Photoluminescence studies of single-crystalline SnO2 grown by chemical vapor transport from SnCl4 and H2O vapors were carried out in the visible spectral range. A non-trivial dependence of the 2.6 eV emission band on temperature and optical excitation level was observed. Based on the obtained data, the ionization energy of a shallow donor in SnO2 was estimated to be 7 meV. Additionally, a model of energy levels and radiative transitions associated with shallow donors and intrinsic defects is proposed.

Solids doi: 10.3390/solids6040067

Authors: Sean Roubion Krishna Prasad Sharma Ganesh Dhakal Guang-Lin Zhao

This study investigates the microwave absorption properties of the cuprate ceramic material Bi1.7Pb0.3Sr2Ca2Cu3O10 (BSCCO) and its composites with bismuth oxide (Bi2O3) in the 4–25 GHz frequency range. Composites with varying BSCCO contents were fabricated and characterized using the Nicolson–Ross–Weir method and Agilent Materials Measurement Software 85071E to determine complex permeability and permittivity. The 4 wt.% BSCCO composite exhibited a peak reflection loss of −32.6 dB at 12.5 GHz, while the 40 wt.% BSCCO composite reached a 52% microwave absorption ratio at 23 GHz. These results demonstrate that microwave absorption is strongly influenced by dielectric properties and the ratio of BSCCO and Bi2O3 composites. This work highlights the potential of BSCCO-Bi2O3 ceramics for microwave absorption applications, particularly in environments experiencing significant temperature gradients due to their thermal stability and electromagnetic performance.

Solids doi: 10.3390/solids6040066

Authors: Chenxing Liao Feng Zhou Wei Xie Liaolin Zhang

Mn4+-doped fluoride red phosphors are widely used in white LED lighting and display applications due to their excellent luminescent properties. However, their synthesis relies heavily on highly toxic aqueous hydrofluoric acid, which not only causes severe environmental and soil/water pollution but also makes it difficult to control the microstructure of the products due to the rapid reaction rate. In this study, low-melting-point NH4HF2 was used as the molten salt, with KMnO4 and MnF2 as manganese sources, to synthesize the red phosphor K3AlF6: Mn4+ via the molten salt method. After the reaction, impurities such as NH4HF2 were removed by washing with a dilute H2O2 solution. The microstructure, photoluminescence properties, thermal quenching behavior, and application in warm white light-emitting diodes (W-LEDs) of the K3AlF6: Mn4+ phosphors were investigated. The results indicate that the phosphors prepared by this method consist of a single pure phase. By adjusting the molten salt content, the morphology of the product can be transformed from nanoparticle-like to nanorod-like structures. All products exhibit the characteristic red emission of Mn4+ under blue and violet light excitation, with the optimally doped sample achieving an internal quantum efficiency (IQE) of 69% under blue light excitation. The combination of the obtained K3AlF6: Mn4+ with the yellow phosphor YAG enabled the fabrication of W-LEDs. These W-LEDs achieved a color rendering index (Ra) of 86.8, a luminous efficacy (LE) of 77 lm/W, and a correlated color temperature (CCT) of 3690 K, along with excellent color stability under operating conditions.

Solids doi: 10.3390/solids6040065

Authors: Fernando Hernández-Navarro Armando Salinas-Rodríguez Rogelio Deaquino-Lara Javier Aguilar-Carrillo Iván A. Reyes-Domínguez Lizangela Guerra-Fuentes Ma. de J. Soria-Aguilar Francisco R. Carrillo-Pedroza Josefina García-Guerra Verónica E. Salazar-Muñoz Emmanuel J. Gutiérrez-Castañeda

In this work, different processing routes were investigated to evaluate the effects of hot rolling temperature, annealing before cold rolling (ABCR), and one- or two-stage cold rolling and annealing schedules to obtain more efficient electrical steels. The correlation between processing variables, microstructure, thickness, and magnetic properties was established from the analysis of 3D surface plots. It was found that the lowest core loss values (3.4 W/kg) were obtained when steel is processed by hot rolling (800 °C), ABCR (880 °C–180 min), first cold rolling (up to 0.25 mm), first annealing (850 °C–10 min), second cold rolling (up to 0.2 mm), and second annealing (850 °C–10 min). The better combination between thickness and grain size leads to the enhancement of the magnetic properties, which affects the way eddy and hysteresis losses contribute to the total core losses.

Solids doi: 10.3390/solids6040064

Authors: Yu Liang Chen Cheng Kun Chu Ya Chih Chang

This study investigates the ballistic performance and energy-absorption behavior of advanced multilayer ceramic composite armor systems composed of silicon carbide (SiC) ceramics, composite metal foam (CMF), rolled homogeneous armor (RHA), ultra-high-molecular-weight polyethylene (UHMWPE), aluminum, and rubber interlayers. The objective is to enhance impact resistance and optimize energy dissipation efficiency against armor-piercing (AP) projectiles. Ballistic tests were performed following the NIJ Standard 0101.06 Level IV specifications using .30” caliber AP M2 rounds with an impact velocity of 784–844 m/s. Experimental results revealed that the SiC front layer effectively fragmented the projectile and dispersed its kinetic energy, while the CMF and UHMWPE layers were the primary energy absorbers, dissipating approximately 70% of the total impact energy (≈3660 J). The aluminum and RHA layers provided additional reinforcement, and the rubber interlayer significantly reduced stress-wave propagation and suppressed crack growth in the ceramic. The most efficient configuration 0.5 mm RHA + 7 mm SiC + 7 mm EPDM + 7 mm CMF + 5 mm UHMWPE achieved an areal density absorption of 77.2 J·m2/kg and a unit thickness absorption of 190.6 J/mm. These findings establish a quantitative layer-wise energy dissipation framework, highlighting the synergistic interaction between brittle, porous, and ductile layers. This work provides practical design principles for developing lightweight, high-efficiency composite armor systems applicable to defense, aerospace, and personal protection fields. Moreover, this study not only validates the NIJ Standard 0101.06 ballistic performance experimentally but also establishes a reproducible methodology for quantitative, layer-wise energy analysis of hybrid ceramic-CMF-fiber armor systems, offering a scientific framework for future model calibration and optimization.

Solids doi: 10.3390/solids6040063

Authors: Ulrich Wulf Jan Kučera

In a series of previous publications an R-matrix approach was developed to describe transport in N-pole quantum devices in the Landauer–Büttiker formalism. Central quantities in this formalism are the transmission coefficients occurring in coherent scattering functions ranging throughout the device. Here we develop the weak formulation version of this approach. It allows to introduce systematically approximations that reduce the exact problem to suitable matrix equations that can be solved on the computer. As a major advantage of our method any approximation found in the weak formulation approach to the R-matrix is current conserving by construction. Here the essential step is the representation of the current S-matrix by a Cayley transform. Restricting us to the one-dimensional case we find that the R-matrix in weak formulation generates a real symmetric Cayley transform by construction. From general theory it follows immediately that the current is conserved.

Solids doi: 10.3390/solids6040062

Authors: Blaise Awola Ayirizia Adrian De la Rocha Valeria I. Arteaga-Muñiz Yu-Hang Tang Wibe A. De Jong Jorge A. Muñoz San Martín

Most machine learning algorithms operate on vectorized data with Euclidean structures because of the significant mathematical advantages offered by Hilbert space, but improved representational efficiency may offset more involved learning on non-Euclidean structures. Recently, a method that integrates the marginalized graph kernel into the Gaussian process regression framework was used to learn directly on molecular graphs. Here, we describe an implementation of this method for crystalline materials based on effective crystal graph representations: the molecular graphs of 128-atom supercells of body-centered cubic (BCC) iron with periodic boundary conditions. Regressors trained on hundreds of time steps of a density functional theory molecular dynamics (DFT-MD) simulation achieved root mean square errors of less than 5 meV/atom. The mechanical stability of BCC iron was investigated at high pressure and elevated temperature using regressors trained on short DFT-MD runs, including at conditions found in the inner core of the earth. Phonon dispersions obtained from the short runs show that BCC iron is mechanically stable at 360 GPa when the temperature is above 2500 K. Atoms in the super cell were displaced in the direction of the first, second, and third nearest-neighbors from selected configurations that included thermal atomic displacements, and forces exerted on the displaced atoms were computed by numerical differentiation of the regressors.

Solids doi: 10.3390/solids6040061

Authors: Carlos Israel Medel Ruiz Roger Chiu Jesús Ricardo Sevilla Escoboza Jesús Castañeda Contreras Francisco Gerardo Peña Lecona Jesús Muñoz Maciel

Phonons, the quantized lattice vibrations, are fundamental for a wide range of phenomena in condensed matter systems. In particular, low-frequency phonons significantly influence electrical conductivity, thermal transport, and the optical properties of solid-state materials. Although there is considerable literature on cadmium sulfide (CdS) phonons—studied, for example, using resonance Raman spectroscopy—up-to-date information on the low-frequency phonons of this important semiconductor is still lacking. In this study, Raman spectroscopy under off- and near-resonance conditions is employed to investigate the low-frequency phonon in wurtzite CdS single crystals. Under off-resonance conditions, the spectrum exhibits multiple low-intensity peaks, which were analyzed through curve fitting. In contrast, the near-resonance spectrum shows an intense, broad band that was deconvoluted into its constituent components, including an antiresonance feature that was mathematically modeled for the first time in CdS. The results demonstrate that Raman scattering intensity in both regimes provides valuable insights into the low-frequency phonon modes of CdS. These findings enhance our understanding of the material’s vibrational properties and may facilitate the development of more efficient CdS-based optoelectronic devices.

Solids doi: 10.3390/solids6040060

Authors: Aleksandr D. Muravev Andrei V. Ivanov Vladimir A. Mukhanov Sergey K. Dedushenko Boris A. Kulnitskiy Alexander V. Vasiliev Natalia V. Maksimova Victor V. Avdeev

Composites in which finely dispersed particles of the metallic phase are uniformly distributed over the surface of expanded graphite can be used as magnetic sorbents for crude oil and petroleum products, as well as a basis for creating screens that protect against electromagnetic radiation. The literature describes various approaches to obtaining such materials, but from a technological point of view, the most promising is the method in which the formation of a metal-containing phase on the surface of expanded graphite is directly combined with its expansion. For this purpose, graphite intercalation compounds with chlorides of metals of the iron triad (GIC-MClx) were obtained: GIC-FeCl3 of I-VII stages, GIC-CoCl2 of I/II stage and GIC-NiCl2 of II/III stage, which were treated with liquid NH3 or CH3NH2 in order to obtain an occlusive complex, which, due to the presence of a large amount of bound RNH2, would be capable of effective thermal expansion during heating in an inert atmosphere with the formation of low-density expanded graphite, and the presence of reducing properties in ammonia and methylamine would lead to the reduction of the metal from chloride. The structure of GIC-MClx and GIC-MClx treated by NH3 and CH3NH2 was investigated by XRD analysis and Mossbauer spectroscopy. The composition of the metal-containing phase in expanded graphite/metal composite was determined by XRD analysis and its quantity by the gravimetric method. The distribution of metals particles is investigated by SEM, TEM and EDX methods. Expanded graphite/metal composites are characterized by the high saturation magnetization (up to ≈ 50 emu/g) at a bulk density of 4–6 g/L.

Solids doi: 10.3390/solids6040059

Authors: Riyad Al Sharif Ayman S. Ayesh Muayad Esaifan Naem Mazahrih Nabeel Bani Hani Bayan Al Rjoub Eva Rayya Majd Abu Salem

This study presents a green and sustainable approach for synthesizing zinc oxide nanoparticles (ZnO-NPs) using Melia azedarach leaf extract as a reducing and stabilizing agent, with zinc acetate as the precursor. The synthesized nanoparticles were thoroughly characterized to assess their structural, morphological, and physicochemical properties, revealing nanoscale dimensions, enhanced crystallinity, and improved stability compared to commercial ZnO. Controlled release experiments under plant-relevant pH conditions demonstrated a gradual and sustained release of Zn2+ ions, accompanied by buffering effects and re-precipitation of Zn(OH)2, highlighting their potential for long-term nutrient availability in soil systems. Unlike conventional studies that focus mainly on synthesis or characterization, this work emphasizes the functional performance of ZnO-NPs as nanofertilizers, combining eco-friendly production with practical agricultural applications. The plant-mediated synthesis yielded nanoparticles with uniform size distribution, enhanced dispersion, and stability, which are critical for efficient nutrient delivery and persistence in soil. Overall, this study provides a cost-effective, scalable, and environmentally benign strategy for producing ZnO nanoparticles and offers valuable insights into the development of sustainable nanofertilizers aimed at improving crop nutrition, soil fertility, and agricultural productivity.

Solids doi: 10.3390/solids6040058

Authors: Hussein Abdul Karin Moussa Johan Alexander Cortés Suárez Felipe de Almeida La Porta Márcio Sousa Góes

This study investigates CaCu3−xSrxTi4O12 (CCSTO) systems synthesized using the solid-state method, with x compositions of 0.00, 0.15, and 3.00. The samples were modified using 6 wt% graphene oxide (GO) and reduced GO (rGO) prepared via Hummer’s method to evaluate their performance as electrodes in supercapacitors. The results indicate that the addition of 6wt% rGO to CCTO (CCTO-6rGO) led to an improvement in specific capacitance, reaching 237.76 mF·g−1 at a scan rate of 10 mV/s, compared to 29.86 mF·g−1 for pure CCTO and only 7.83 mF·g−1 for CCTO-6GO, suggesting that rGO enhances charge storage. For the CCTO15Sr samples, CCTO15Sr-6rGO exhibited the highest specific capacitance, with 321.63 mF·g−1 at 10 mV/s, surpassing both pure CCTO15Sr (80.19 mF·g−1) and CCTO15Sr-6GO (25.73 mF·g−1). These results stem from oxygen and metal vacancies, which aid charge accumulation and ion diffusion. In contrast, adding GO generally reduced specific capacitance in all samples. The findings highlight CCSTO’s potential—especially with rGO modification—as a supercapacitor electrode while also indicating areas for further optimization.

Solids doi: 10.3390/solids6040057

Authors: Galiia Korznikova Gulnara Khalikova Igor Kosarev Wei Wei Alexander Semenov Elena Korznikova

This study investigates the microstructure and mechanical properties of copper (Cu) and graphene/Cu (Gr/Cu) composites produced via high-pressure torsion (HPT) under 5 GPa at room temperature. Microstructural analysis revealed significant grain refinement, with average grain sizes of 0.39 μm for pure Cu and 0.35 μm for Gr/Cu composite. The Gr/Cu composite exhibited slightly higher microstrains and effective stacking fault energy (SFE). Tensile tests showed ultimate tensile strengths of 689 MPa (pure Cu) and 674 MPa (Gr/Cu), with the latter demonstrating improved ductility (~10% elongation). Ab initio calculations confirmed a 27% increase in SFE for Gr/Cu, aligning with experimental results. These findings highlight the potential of Gr/Cu composites for applications requiring high strength and efficient heat dissipation.

Solids doi: 10.3390/solids6040056

Authors: Ather Syed Mahendra Kumar Samal

Nuclear fuel cladding serves as the primary barrier to the release of radioactive fission products and is subjected to high-temperature and high-pressure environments during both normal reactor operation and accident scenarios such as loss of coolant accidents (LOCAs). Predicting the burst behavior of cladding is essential for ensuring structural integrity, especially under varying heating rates—an aspect inadequately addressed in existing empirical models. In this study, a finite element-based damage model is developed to simulate the ballooning and burst behavior of Zircaloy-4 cladding. The model incorporates creep deformation, stress triaxiality, and time-dependent damage accumulation. Material behavior is characterized using experimentally determined creep constants and the model is calibrated against burst test data from the literature. A new heating-rate-dependent burst correlation is proposed based on model outputs. The results indicate that increasing the heating rate raises the burst temperature due to reduced exposure time in the temperature regime where creep damage accumulates significantly. The model accurately reproduces burst behavior across a wide range of internal pressures (1–10 MPa) and heating rates (5–100 °C/s). The newly developed correlation improves predictive capability in accident analysis tools and can be directly implemented into safety analysis codes for Indian pressurized heavy water reactors (PHWRs), contributing to enhanced reactor safety evaluations.

Solids doi: 10.3390/solids6040055

Authors: Zhussupbek M. Salikhodzha Guldari B. Bairbayeva Anatoli I. Popov Raigul N. Kassymkhanova Keleshek B. Zhangylyssov Elena Popova Marina Konuhova

This work presents a theoretical investigation of ionic conductivity in cubic zirconia (c-ZrO2) doped with magnesium, using density functional theory (DFT) with the hybrid B3LYP functional as implemented in the CRYSTAL23 software package. It was found that the spatial arrangement of magnesium atoms and oxygen vacancies significantly affects the energy barriers for oxygen ion migration. Configurations with magnesium located along and outside the migration path were analyzed. The results show that when Mg2+ is positioned along the migration trajectory and near an oxygen vacancy, stable defect complexes are formed with minimal migration barriers ranging from 0.96 to 1.32 eV. An increased number of Mg atoms can lead to a further reduction in the barrier, although in certain configurations the barriers increase up to 3.0–4.6 eV. When doping occurs outside the migration path, the energy profile remains symmetric and moderate (0.9–1.1 eV), indicating only a weak background influence. These findings highlight the critical role of coordinated distribution of Mg atoms and oxygen vacancies along the migration pathway in forming efficient ion-conducting channels. This insight offers potential for designing high-performance zirconia-based electrolytes for solid oxide fuel cells and sensor applications.

Solids doi: 10.3390/solids6030054

Authors: Alireza Vahdati Mehdi Salehi Meisam Vahabi Aazam Ghassemi Javad Jafari Fesharaki Soheil Oveissi

Dynamic behavior of coaxial axisymmetric planar cracks in the transversely isotropic magneto-electro-elastic (MEE) material in transient in-plane magneto-electro-mechanical loading is studied. Magneto-electrically impermeable as well as permeable cracks are assumed for crack surfaces. In the first step, considering prismatic and radial dynamic dislocations, electric and magnetic jumps are obtained through Laplace and Hankel transforms. These solutions are utilized to derive singular integral equations in the Laplace domain for the axisymmetric penny-shaped and annular cracks. Derived Cauchy singular type integral equations are solved to obtain the density of dislocation on the crack surfaces. Dislocation densities are utilized in computation of the dynamic stress intensity factors, electric displacement, and magnetic induction in the vicinity tips of crack tips. Finally, some numerical case studies of single and multiple cracks are presented. The effect of system parameters on the results is then discussed.

Solids doi: 10.3390/solids6030053

Authors: Chenxing Liao Huihuang Cai Dongyuan Dai Liaolin Zhang

Mg2TiO4:Mn4+ (MTO:Mn4+) red phosphor has important applications in areas such as red LEDs and forensic science, but the preparation of MTO:Mn4+ through the solid-state reaction method requires a high sintering temperature. Herein, MTO:Mn4+ red phosphor was synthesized using the solid-state reaction method with LiCl flux, and its crystallographic structure and photoluminescence properties were studied to determine the influence of experimental parameters like the amount of fluxing agent added and sintering temperature in producing a bright red phosphor suitable for LEDs. The experimental results showed that samples with added LiCl could form pure MTO after sintering at 950 °C, whereas those without LiCl still contained a mixture of MTO and MgTiO3, even when sintered at 1400 °C. The optimal performance was achieved with a sample doped with 0.2 mol% Mn4+, synthesized using 50 wt% LiCl flux and sintered at 950 °C for 12 h. This sample exhibited a broad excitation band and a narrow red emission band peaking at 662 nm, confirming its excellent luminescence properties. Furthermore, a prototype red LED fabricated with a 377 nm chip and MTO:0.2% Mn4+ phosphor achieved photoelectric conversion efficiency of 78.5% at a 100 mA drive current, confirming its viability for high-performance red LED manufacturing.

Solids doi: 10.3390/solids6030052

Authors: Michael A. Reshchikov

Gallium Nitride (GaN) is a wide-bandgap semiconductor that has revolutionized optoelectronic applications, enabling blue/white light-emitting devices and high-power electronics. Point defects in GaN strongly influence its optical and electronic properties, producing both beneficial and detrimental effects. This review provides a comprehensive update on the current understanding of point defects in GaN and their impact on photoluminescence (PL). Since our earlier review (Reshchikov and Morkoç, J. Appl. Phys. 2005, 97, 061301), substantial progress has been made in this field. PL bands associated with major intrinsic and extrinsic defects in GaN are now much better understood, and several defects in undoped GaN (arising from unintentional impurities or specific growth conditions) have been identified. Notably, the long-debated origin of the yellow luminescence band in GaN has been resolved, and the roles of Ga and N vacancies in the optical properties of GaN have been revised. Zero-phonon lines have been discovered for several defects. Key parameters, such as electron- and hole-capture coefficients, phonon energies, electron–phonon coupling strength, thermodynamic charge transition levels, and the presence of excited states, have been determined or refined. Despite these advances, several puzzles associated with PL remain unsolved, highlighting areas for future investigation.

Solids doi: 10.3390/solids6030051

Authors: Yuta Nakayama Masayuki Ogawa Jun Tatebayashi Yukihiro Harada Yasufumi Fujiwara Takashi Kita

We theoretically studied the control of the extraction of anti-Stokes photoluminescence using photonic crystal (PhC) nanocavities. Our fabricated (erbium,oxygen)-codoped GaAs PhC nanocavity showed a positive feedback gain of heating through the excitation of the GaAs host, which suggests the possibility of higher laser-cooling efficiencies at lower temperatures in such systems. Based on this result, we constructed a theoretical framework of laser cooling in PhC nanocavities. The predicted laser cooling efficiency of a PhC nanocavity is six to eight times higher than that of the corresponding bulk system, and we predict that more than 24% can be achieved at 100 K using holmium-doped materials.

Solids doi: 10.3390/solids6030050

Authors: Yin Liu Wenhao Shen Douglas W. Coffin Tao Song Jean-Francis Bloch Jean-Pierre Corriou

An improved Mass–Spring Model (iMSM) is developed by adding central springs to the conventional Mass–Spring Models (MSMs) of tubular structures. This improvement is necessary to model fibers that have enough stiffness so that they do not collapse under transverse loading. Such is the case with many pulp fibers used in papermaking. Four different types of pulp fibers (Aspen CTMP, Aspen BCTMP, Birch BCTMP, and Spruce BKP) were simulated in the study. A geometric model and iMSM of a single fiber were developed, in which the topological structure of iMSM is explained in detail. The mass of mass points and the elastic coefficient of different springs in iMSM were calculated using axial tensile and torsional responses. A dynamic simulation of transverse bending of the fiber over a rigid cylinder and subjected to a transverse pressure was used to determine the effective elastic modulus for four different single fibers and compared to experimental values with an average relative error of 8.49%. The dynamic simulations were completed in 1.04–2.64 min for the four different paper fibers representing sufficient speeds to meet the needs of most real application scenarios. The acceptable accuracy and the fast simulation speed with the developed iMSM fiber model demonstrate the feasibility of the methodology in analyzing paper structures as well as similar fiber-based materials.

Solids doi: 10.3390/solids6030049

Authors: Xinyue Jing Minxuan Chen Xingye Ma Xinrui Xu Ning Wang Kunpeng Niu Xiaohan Chen Yihao Wang Jiayi Zhu Jianguo Hou Zhichao Wang

As a vital transition metal species, cobalt ions (Co2+) play a critical role in industrial and medical fields. However, uncontrolled release into ecosystems via industrial effluents presents significant environmental risks. To address this, a prism-coupled surface plasmon resonance (SPR) sensor chip was developed which enables simultaneous high sensitivity, wide detection range, and rapid detection of Co2+ under ultra-low detection limit conditions. By depositing a 50 nm Au film and AuNPs on a glass substrate, and integrating carboxyl-functionalized carbon quantum dots (CQDs), the chip achieved the detection range of 10−20 mol/L to 10−4 mol/L, and the response time was reduced from 21 min to 11 min under optimal electric field conditions (1.2 V, 0.15 mol/L electrolyte concentration). The sensor exhibits high selectivity, repeatability, and stability. It can be integrated with optofluidic technology to enable high-throughput microfluidic analysis, thereby facilitating further advancements in related research.

Solids doi: 10.3390/solids6030048

Authors: Bogdan-Ovidiu Taranu Paula Svera Gabriel Buse Maria Poienar

Hydrogen generation has become a popular research subject in light of currently pressing issues, such as the rapidly increasing environmental pollution, the depleting fossil fuel reserves, and the looming energy crisis. Sustainable electrochemical water splitting is regarded as one of the most desirable methods for obtaining green hydrogen. Considering this state of affairs, the water splitting electrocatalytic activity of glassy carbon electrodes modified with birnessite-type K2Mn4O8 and mixed-valence iron phosphate Fe3(PO3OH)4(H2O)4 materials were evaluated in electrolyte solutions having different pH values. Both compounds were characterized by X-ray diffraction and FT-IR spectroscopy in order to analyze their phase purity and their structural features. The most catalytically active birnessite-type K2Mn4O8-based electrode was manufactured using a catalyst ink containing only the electrocatalyst dispersed in ethanol and Nafion solution. In 0.1 M H2SO4, it exhibited an oxygen evolution reaction (OER) overpotential of 1.07 V and a hydrogen evolution reaction (HER) overpotential of 0.957 V. The Tafel slopes obtained in the OER and HER experiments were 0.180 and 0.142 V/dec, respectively. The most catalytically active mixed-valence iron phosphate Fe3(PO3OH)4(H2O)4-based electrode was obtained with a catalyst ink containing the specified material mixed with carbon black and dispersed in ethanol and Nafion solution. In a strongly alkaline medium, it displayed a HER overpotential of 0.515 V and a Tafel slope value of 0.122 V/dec. The two electrocatalysts have not been previously investigated in this way, and the acquired data provide insights into their electrocatalytic activity and improve the scientific understanding of their properties and applicative potential.

Solids doi: 10.3390/solids6030047

Authors: Jiabin Tian Ziyi Yang Yayun Zheng Zhengfei Chen

Despite notable advancements in lithium-ion battery (LIB) technology, growing industrialization, rising energy demands, and evolving consumer electronics continue to raise performance requirements. As the primary determinant of battery performance, cathode materials have become a central research focus. Among emerging candidates, iron-based fluorides show great promise due to their high theoretical specific capacities, elevated operating voltages, low cost (owing to abundant iron and fluorine), and structurally diverse crystalline forms such as pyrochlore and tungsten bronze types. These features make them strong contenders for next-generation high-energy, low-cost LIBs. This review highlights recent progress in iron-based fluoride cathode materials, with an emphasis on structural regulation and performance enhancement strategies. Using pyrochlore-type hydrated iron trifluoride (Fe2F5·H2O), synthesized via ionic liquids like BmimBF4, as a representative example, we discuss key methods for tuning physicochemical properties—such as electronic conductivity, ion diffusion, and structural stability—via doping, compositing, nanostructuring, and surface engineering. Advanced characterization tools (XRD, SEM/TEM, XPS, Raman, synchrotron radiation) and electrochemical analyses are used to reveal structure–property–performance relationships. Finally, we explore current challenges and future directions to guide the practical deployment of iron-based fluorides in LIBs. This review provides theoretical insights for designing high-performance, cost-effective cathode materials.

Solids doi: 10.3390/solids6030046

Authors: Florentino Alvarez-Antolin Alejandro González-Pociño

This study investigates the influence of key heat treatment parameters on the microstructure and mechanical properties of the powder metallurgy tool steel Vanadis 60. A fractional factorial design of experiments was applied to evaluate the effects of austenitising temperature, quenching medium, tempering temperature, and number of tempering cycles on hardness, flexural strength, and microstructure, using detailed phase characterisation by X-ray diffraction. The results reveal two distinct processing routes tailored to different performance objectives. Maximum hardness was achieved by combining austenitisation at 1180 °C, rapid oil quenching, and tempering at 560 °C. These conditions enhance the solubility of carbon and other alloying elements, promote secondary hardening, and reduce retained austenite. Conversely, higher toughness and ductility were obtained by austenitising at 1020 °C, air cooling, and tempering at 560 °C. These parameters favour the formation of a bainitic microstructure, together with lower martensite tetragonality and minimal retained austenite. A statistically significant interaction was identified between the austenitising temperature and the number of tempering cycles; three temperings were sufficient to compensate for the lower hardness associated with reduced austenitising temperatures. The results provide a robust guidance for optimising thermal processing in highly alloyed tool steels, enabling the precise tailoring of microstructure and properties in accordance with specific mechanical service requirements.

Solids doi: 10.3390/solids6030045

Authors: Pengfei Wang Haiyang Yu Chengyan Zou Yuxue Wu Zhengfei Chen

Due to its unique layered structure that facilitates ion intercalation and deintercalation, δ-MnO2 has emerged as a promising cathode material for aqueous zinc-ion batteries (ZIBs). However, its structural collapse and Mn dissolution during prolonged cycling significantly limit its practical application. In this study, we demonstrate that metal ion doping, particularly with Fe3+, can effectively stabilize the δ-MnO2 structure and enhance its electrochemical performance. Through a hydrothermal synthesis approach, δ-MnO2 materials with varying Fe3+ doping ratios are prepared and systematically investigated. Among them, the sample with a Mn:Fe molar ratio of 20:1 exhibits the best performance, maintaining the layered δ-MnO2 phase while significantly increasing Mn3+ content and promoting the formation of oxygen vacancies. At a current density of 0.5 A·g−1, the iron-doped sample exhibited an initial specific capacity of 116.24 mAh·g−1, with a capacity retention rate of 41.7% after 200 cycles. In contrast, the undoped δ-MnO2 showed an initial specific capacity of only 85.15 mAh·g−1, with a capacity retention rate of merely 19.9% after 200 cycles. The results suggest that Fe3+ doping not only suppresses Mn dissolution but also improves structural stability and Zn2+ transport kinetics. This work provides new insights into the development of durable Mn-based cathode materials for aqueous ZIBs.

Solids doi: 10.3390/solids6030044

Authors: Abdelfattah Boukhssim Hassan Yassine Gérard Leroy Jean-Claude Carru Manuel Mascot Christophe Poupin Mohammad Kassem

Aging studies of lithium-ion batteries are essential for understanding material degradation, which impacts performance and, consequently, battery lifespan. In this paper, we propose the use of electrochemical impedance spectroscopy, differential capacity analysis, and electrochemical noise measurements to evaluate the effects of different C-rates (2C, C/2, and C/20) on a cell. We study aging up to 800 charge/discharge cycles. We demonstrate that aging is associated with a linear increase in electrode resistance, which correlates with capacity fading. Additionally, noise measurements indicate a rise in noise levels at low frequencies following a 1/fγ trend with 1<γ<2.

Solids doi: 10.3390/solids6030043

Authors: Fatih Doğan Erhan Duru

Shape memory alloys (SMAs) are known for their exceptional mechanical properties, particularly their superior wear resistance compared to conventional alloys with similar surface hardness. Rare earth oxides are often used as additives to further improve these characteristics. This study investigates the effects of different CeO2 (cerium dioxide) concentrations (0.01 wt.%, 0.1 wt.%, 0.5 wt.%, and 1.0 wt.%) on the properties of CuAlMnFe alloys produced via powder metallurgy (PM). Various analyses were performed, including scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD), as well as hardness, wear, and corrosion tests. The increase in wear rate is closely related to the formation of precipitates from CeO2 addition. Improvements in wear resistance and hardness are attributed to the effects of grain refinement and solid solution strengthening due to CeO2. Specifically, the wear rate increased from 1.5 × 10−3 mm3/(Nm) to 3.4 × 10−3 mm3/(Nm) with higher CeO2 content. Additionally, the friction coefficient of the CuAlMnFe alloy was reduced with CeO2 addition, indicating enhanced frictional properties. The optimal CeO2 concentration of 0.5% was found to improve grain uniformity, resulting in better wear resistance. Incorporating CeO2 particles into CuAlMnFe alloy enhances hardness and reduces wear rate when used in appropriate amounts. Additionally, it exhibits superior corrosion resistance, as evidenced by a positive shift in corrosion potential in Tafel measurements in solutions and a decrease in corrosion current density. The C0.5 specimen showed the highest corrosion potential (Ecorr, −588 V) and the lowest corrosion current density (icorr, 6.17 μA/cm2) during electrochemical corrosion in 3.5 wt.% NaCl solution.

Solids doi: 10.3390/solids6030042

Authors: Zinan Zhong Zilong Zhang Fu Li Yuexing Chen Jingting Luo Zhuanghao Zheng

Ag2Se has attracted significant attention as a promising alternative to Bi2Te3 for near-room-temperature thermoelectric (TE) applications. In this study, flexible Ag2Se thin films were fabricated via magnetron sputtering under different sputtering power settings, followed by post-deposition annealing to optimize their TE properties. Structural and compositional analyses confirmed the successful synthesis of Ag2Se films with high crystallinity. Additionally, tuning the sputtering power and annealing temperatures can effectively enhance the electrical conductivity, Seebeck coefficient, and overall power factor. A significant power factor of ~17.4 µW·cm−1·K−2 at 100 °C was achieved in the 30 W sputtering power and 300 °C annealing sample, pointing out the huge potential of Ag2Se thin films as self-powered flexible devices.

Solids doi: 10.3390/solids6030041

Authors: Jorge Alexandre Alencar Fotius Helinando Pequeno de Oliveira

MXenes, a class of two-dimensional transition metal carbides and nitrides, emerged as a promising material for next-generation energy storage and corresponding applications due to their unique combination of high electrical conductivity, tunable surface chemistry, and lamellar structure. This review highlights recent advances in MXene-based composites, focusing on their integration into electrode architectures for the development of supercapacitors, batteries, and multifunctional devices, including triboelectric nanogenerators. It serves as a comprehensive overview of the multifunctional capabilities of MXene-based composites and their role in advancing efficient, flexible, and sustainable energy and sensing technologies, outlining how MXene-based systems are poised to redefine multifunctional energy platforms. Electrochemical performance optimization strategies are discussed by considering surface functionalization, interlayer engineering, scalable synthesis techniques, and integration with advanced electrolytes, with particular attention paid to the development of hybrid supercapacitors, triboelectric nanogenerators (TENGs), and wearable sensors. These applications are favored due to improved charge storage capability, mechanical properties, and the multifunctionality of MXenes. Despite these aspects, challenges related to long-term stability, sustainable large-scale production, and environmental degradation must still be addressed. Emerging approaches such as three-dimensional self-assembly and artificial intelligence-assisted design are identified as key challenges for overcoming these issues.

Solids doi: 10.3390/solids6030040

Authors: Satoru Hayami

Noncoplanar spin textures give rise not only to unusual magnetic structures but also to emergent electromagnetic responses stemming from scalar spin chirality, such as the topological Hall effect. In this study, we theoretically investigate nonreciprocal transport phenomena induced by noncoplanar magnetic orderings through microscopic model analyses. By focusing on meron–antimeron spin textures that exhibit local scalar spin chirality while maintaining vanishing global chirality, we demonstrate that the electronic band structure becomes asymmetrically modulated, which leads to the emergence of nonreciprocal transport. The present mechanism arises purely from the noncoplanar magnetic texture itself and requires neither net magnetization nor relativistic spin–orbit coupling. We further discuss the potential relevance of our findings to the compound Gd2PdSi3, which has been suggested to host a meron–antimeron crystal phase at low temperatures.

Solids doi: 10.3390/solids6030039

Authors: Yachun Mao Yanqiu Xu Shiru Le Maozhong An Zhijiang Wang Yuhan Zhang

Tungsten and tungsten alloys are widely used in important industrial fields due to their high density, hardness, melting point, and corrosion resistance. However, machining often leaves processing marks on their surface, significantly affecting the surface quality of precision components in industrial applications. Electrolytic polishing offers high efficiency, low workpiece wear, and simple processing. In this study, an electrolytic polishing method is adopted and a novel trisodium phosphate–sodium hydroxide electrolytic polishing electrolyte is developed to study the effects of temperature, voltage, polishing time, and solution composition on the surface roughness of a tungsten–nickel–iron alloy. The optimal voltage, temperature, and polishing time are determined to be 15 V, 55 °C, and 35 s, respectively, when the concentrations of trisodium phosphate and sodium hydroxide are 100 g·L−1 and 6 g·L−1. In addition, glycerol is introduced into the electrolyte as an additive. The calculated LUMO value of glycerol is −5.90 eV and the HOMO value is 0.40 eV. Moreover, electron enrichment in the hydroxyl region of glycerol can form an adsorption layer on the surface of the tungsten alloy, inhibit the formation of micro-pits, balance ion diffusion, and thus promote the formation of a smooth surface. At 100 mL·L−1 of glycerol, the roughness of the tungsten–nickel–iron alloy decreases significantly from 1.134 μm to 0.582 μm. The electrochemical polishing mechanism of the tungsten alloy in a trisodium phosphate electrolyte is further investigated and explained according to viscous film theory. This study demonstrates that the trisodium phosphate–sodium hydroxide–glycerol electrolyte is suitable for electropolishing tungsten–nickel–iron alloys. Overall, the results support the application of tungsten–nickel–iron alloy in the electronics, medical, and atomic energy industries.

Solids doi: 10.3390/solids6030038

Authors: Mengjiao Wu Xiaoling Lei Haiping Fang

Two-dimensional (2D) crystals which present unconventional stoichiometries on graphene surfaces in ambient conditions, such as Na2Cl, Na3Cl, and CaCl, have attracted significant attention in recent years due to their electronic structures and abnormal cation–anion ratios, which differ from those of conventional three-dimensional crystals. This unconventional crystallization is attributed to the cation–π interaction between ions and the π-conjugated system of the graphene surface. Consequently, their physical and chemical properties—including their electrical, optical, magnetic, and mechanical characteristics—often differ markedly from those of conventional crystals. This review summarizes the recent progress made in the fabrication and analysis of the structures, distinctive features, and applications of these 2D unconventional stoichiometry crystals on graphene surfaces in ambient conditions. Their special properties, including their piezoelectricity, metallicity, heterojunction, and room-temperature ferromagnetism, are given particularly close attention. Finally, some significant prospects and further developments in this exciting interdisciplinary field are proposed.

Solids doi: 10.3390/solids6030037

Authors: Tianci Han Yunjie Yin

Polylactic acid (PLA) fabrics exhibit significant sunlight reflectivity and high emissivity within the atmospheric window, making them suitable as the foundational material for this study. This research involves the modification of one side of the fabric with hydrophilic agents and titanium dioxide (TiO2), while the opposite side is treated with MXene and subsequently coated with polydimethylsiloxane (PDMS) to inhibit oxidation of the MXene. Through these surface modifications, a thermal management fabric based on PLA was successfully developed, capable of passively regulating temperature in response to environmental conditions and user requirements. The study discusses the optimal concentrations of TiO2 and MXene for the fabric, and characterizes and evaluates the functional surface of the PLA. Surface morphology analyses and tests indicate that the resulting functional PLA fabrics possess excellent ultraviolet (UV) resistance, favorable air permeability, high sunlight reflectivity on the TiO2-treated side, and superior photothermal conversion capabilities on the MXene-treated side. Furthermore, photothermal effect tests conducted under a light intensity of 1000 W/m2 reveal that the MXene-treated fabric exhibits a heating effect of approximately 25 °C, while the TiO2-treated side demonstrates a cooling effect exceeding 5 °C. This study developed PLA functional fabrics with heating and cooling capabilities.

Solids doi: 10.3390/solids6030036

Authors: Afia Aziz Kona Aaron Lutheran Alireza Tabarraei

This study employs molecular dynamics (MD) simulations to investigate the mechanical response and fracture behavior of penta-graphene, a novel two-dimensional carbon allotrope composed entirely of pentagonal rings with mixed sp2–sp3 hybridization and pronounced mechanical anisotropy. Atomistic simulations are carried out to evaluate the impact of structural defects on mechanical performance and to elucidate crack propagation mechanisms. The results reveal that void defects involving sp3-hybridized carbon atoms cause a more significant degradation in mechanical strength compared to those involving sp2 atoms. During fracture, local atomic rearrangements and bond reconstructions lead to the formation of energetically favorable ring structures—such as hexagons and octagons—at the crack tip, promoting enhanced energy dissipation and fracture resistance. A central focus of this work is the evaluation of the critical stress intensity factor (SIF) under mixed-mode (I/II) loading conditions. The simulations demonstrate that the critical SIF is influenced by the loading phase angle, with pure mode I exhibiting a higher SIF than pure mode II. Notably, penta-graphene shows a critical SIF significantly higher than that of graphene, indicating exceptional fracture toughness that is rare among ultra-thin two-dimensional materials. This enhanced toughness is primarily attributed to penta-graphene’s capacity for substantial out-of-plane deformation prior to failure, which redistributes stress near the crack tip, delays crack initiation, and increases energy absorption. Additionally, the study examines crack growth paths as a function of loading phase angle, revealing that branching and kinking can occur even under pure mode I loading.

Solids doi: 10.3390/solids6030035

Authors: Nosheen Blouch Syed Noman Hussain Kazmi Nijah Akram Muhammad Junaid Saleem Imran Ahmad Khan Kashif Javed Sajjad Ahmad Asfandyar Khan

The cements industry is increasingly under pressure to reduce carbon emissions while maintaining performance standards. Limestone calcined clay cement (LC3) presents a promising low-carbon alternative; however, its performance depends significantly on the type and reactivity of clay used. This study investigates the effect of three common low-grade clay minerals—kaolinite, montmorillonite, and illite—on the behavior of LC3 blends. The clays were thermally activated and characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray fluorescence spectroscopy (XRF), and Blaine air permeability testing to evaluate their mineralogical composition, thermal behavior, chemical content, and fineness. Pozzolanic reactivity was assessed using the modified Chapelle test. Microstructural development was examined through scanning electron microscopy (SEM) of the hydrated specimens at 28 days. The results confirmed a strong correlation between clay reactivity and hydration performance. Kaolinite showed the highest reactivity and fineness, contributing to a dense microstructure with reduced portlandite and enhanced formation of calcium silicate hydrate. Montmorillonite demonstrated comparable strength and favorable hydration characteristics, while illite, though less reactive initially, showed acceptable long-term behavior. Although kaolinite delivered the best overall performance, its limited availability and higher cost suggest that montmorillonite and illite represent viable and cost-effective alternatives, particularly in regions where kaolinite is scarce. This study highlights the suitability of regionally available, low-grade clays for use in LC3 systems, supporting sustainable and economically viable cement production.

Solids doi: 10.3390/solids6030034

Authors: Tianlong He Qiuchun Lu Xidi Sun

Perovskite bionic eyes have emerged as highly promising candidates for photodetection applications to their wide-angle imaging capabilities, high external quantum efficiency(EQE), and low-cost fabrication and integration. Since their initial exploration in 2015, significant advancements have been achieved in this field, with their EQE reaching 27%. Nevertheless, intrinsic challenges such as the oxidation susceptibility of perovskites and difficulties in curved surface growth hinder their further development. Addressing these issues necessitates a comprehensive and systematic understanding of the preparation mechanisms for hemispherical perovskite, as well as the development of effective mitigation strategies. In this review, a review published provides a detailed overview of the research progress in hemispherical perovskite photodetectors, with a particular focus on the fundamental properties and fabrication pathways of hemispherical perovskites. Furthermore, various strategies to enhance the performance of hemispherical perovskite and overcome preparation challenges are thoroughly discussed. Finally, existing challenges and perspectives are presented to further advance the development of eco-friendly hemispherical perovskite.

Solids doi: 10.3390/solids6030033

Authors: Chu-Hsuan Lin Li-Cyuan Huang

With a low surface recombination velocity, it is possible to increase the efficiency of solar cells as the thickness is decreased. A maximum appearing in the efficiency versus thickness curve is mostly due to the same trend in the short-circuit current versus thickness curve. The trend of the short-circuit current versus thickness curve will be clearly discussed based on the view of competition between generation and recombination rates near the rear surface. If surface passivation can be well introduced, the win-win situation for the material cost and efficiency can be achieved based on our results.

Solids doi: 10.3390/solids6030032

Authors: Md Tohidul Islam Catalina Victoria Ruiz Claudia Loyola Joaquin Peralta Scott R. Broderick

Understanding how crystal structure influences electronic properties is crucial for discovering new functional materials. In this study, we utilized Kernel Principal Component Analysis (KPCA) to classify and analyze the Density of States (DOS) of transition metal sulfide (TMS) compounds, particularly copper-based sulfides. By mapping high-dimensional DOS data into a lower-dimensional space, we identify clusters corresponding to different crystal systems and detect outliers with significant deviations from their expected groups. These outliers exhibit unusual electronic configurations, suggesting potential applications in semiconductors, thermoelectric devices, and optoelectronic devices. Projected Density of States (PDOS) analysis further reveals how orbital hybridization governs the electronic structure of these materials, highlighting key differences between structurally similar compounds. Additionally, we analyze phase stability through inter-cluster distance measurements, identifying potential phase transformations between closely related structures. The implications for this work in terms of modifying chemistries and generalized DOS predictions are discussed.

Solids doi: 10.3390/solids6030031

Authors: Chih-Hsi Peng Yi-Cheng Lin

This study presents the first comprehensive theoretical investigation utilizing SCAPS-1D simulation to systematically evaluate eight hole transport materials for CsPbI2Br perovskite solar cells under authentic indoor LED conditions (560 lux, 5700 K color temperature). Unlike previous studies employing simplified illumination assumptions, our work establishes fundamental design principles for indoor photovoltaics through rigorous material property correlations. The investigation explores the influence of layer thickness and defect concentration on performance to identify optimal parameters. Through detailed energy band alignment analysis, we demonstrate that CuI achieves superior performance (PCE: 23.66%) over materials with significantly higher mobility, revealing that optimal band alignment supersedes carrier mobility under low-light conditions. Analysis of HTL and absorber layer thickness, bulk defect concentration, interface defect density, and an HTL-free scenario showed that interface defect concentration and absorber layer parameters have greater influence than HTL thickness. Remarkably, ultra-thin HTL layers (0.04 μm) maintain >99% efficiency, offering substantial cost reduction potential for large-scale manufacturing. Under optimized conditions of a 0.87 μm absorber layer thickness, defect concentration of 1015 cm−3, interface defect concentration of 109 cm−3, and CuI doping concentration of 1017 cm−3, PCE reached 28.57%, while the HTL-free structure achieved 17.6%. This study establishes new theoretical foundations for indoor photovoltaics, demonstrating that material selection criteria differ fundamentally from outdoor applications.

Solids doi: 10.3390/solids6020030

Authors: Baoyun Liang Ang Li Ziming Kuang Yating Qu Hao Xu Tianyi Tang Tingting Shi Weiguang Xie

In the quest for stable, lead-reduced perovskites, this study unravels the structural and electronic evolution of CsZnI3 across its α, β, and γ phases. DFT calculations spotlight the tetrahedral γ phase—with elongated Zn–I bonds (3.17 Å)—as the most stable, sidestepping the octahedral distortions of its metallic α and β counterparts. Pb2+ doping (>50%) drives a transformation to mixed octahedral–tetrahedral coordination, slashing the wide 3.15 eV bandgap to a solar-optimal 2.20 eV via lattice shrinkage. Above 50% doping, an optimum emerges—balancing structural integrity with efficient light absorption. These findings elevate Zn-doped or Zn-Pb-based compounds as promising and tunable perovskites for next-gen photovoltaics.

Solids doi: 10.3390/solids6020029

Authors: Alejandro Garrote-Márquez Norge Cruz Hernández Eduardo Menéndez-Proupin

This study investigates the potential correlation between C—H···Br and N—H···Br hydrogen bonds in CH3NH3PbBr3 over a broad temperature range (50–350 K), using a statistical analysis of molecular dynamics simulations. The analysis focused on quantifying the relationship between both hydrogen bond types via Pearson and Spearman correlation coefficients, derived from extensive datasets obtained from simulation trajectories. The results revealed a notable discrepancy between the two coefficients at low temperatures (T ≤ 125 K): While Spearman’s values suggested a strong monotonic correlation, Pearson’s values indicated a lack of linear association. Further analysis through data segmentation and block averaging demonstrated that the high Spearman coefficients at low temperatures were not statistically robust. At higher temperatures (T > 125 K), both correlation coefficients consistently exhibited low values, confirming the absence of meaningful correlation. These findings suggest that the formation of C–H···Br and N–H···Br hydrogen bonds occurs independently, with no evidence of cooperative behavior.

Solids doi: 10.3390/solids6020028

Authors: Lucas Henrique Pereira Silva Jacqueline Roberta Tamashiro Fabio Friol Guedes de Paiva João Henrique da Silva Rego Miguel Angel de la Rubia Angela Kinoshita Amparo Moragues Terrades

Global cement manufacturing generated 1.6 billion metric tons of CO2 in 2022 and relies heavily on non-renewable raw materials. Utilizing agro-industrial waste as supplementary cementitious material (SCM) can help mitigate the demand for these resources. SCMs have been integrated into cement production to deliver both technical and environmental benefits to mortars and concrete. This study examines mortar blends containing blast furnace slag (BFS), Brazilian calcined clay (BCC), and bamboo leaf ash (BLA). While BFS and BCC are already established in the cement industry, recent research has highlighted BLA as a promising pozzolanic material. The SCMs were characterized, and mortars were produced to assess their flexural and compressive strength, as well as durability indicators such as electrical resistivity, chloride diffusion, migration coefficient, and carbonation resistance. The findings reveal significant performance enhancements. Partial cement replacement (20% and 40%) maintained the strength of both binary and ternary mortars, demonstrating statistical equivalence to the reference mortar (p > 0.05). It also contributed to an improved pore structure, reducing the migration coefficient by up to four times in the 20BLA20BCC mix (which replaces 20% of cement with BLA and 20% with BCC) compared to the reference mix. Chemically, the SCMs enhanced the chloride-binding capacity of the cementitious matrix by up to seven times in the case of the 20BCC mortar, thereby improving its durability. Therefore, all tested compositions—binary and ternary—showed mechanical and durability advantages over the reference while also contributing to the reduction in environmental impacts associated with the cement industry.

Solids doi: 10.3390/solids6020027

Authors: Qian Guo Jie Wang Yanchun Li Ramón Artiaga

Many factors and their mutual interaction between catalysts and AP/HTPB composite solid propellant induce the complexity in the combustion. Among them, we prepared two Fe-based MOFs as catalysts and investigated their catalytic effects and mechanism on the decomposition AP, HTPB and AP/HTPB complex by TG-DSC and TG-IR. The results show that both Fe-based MOFs exhibit catalytic effects on the decomposition of all samples. Specifically, in the AP/HTPB/MOFs composite system, a synergistic effect between MOFs and HTPB is observed, substantially accelerating the decomposition of both AP and HTPB, which makes the HTD temperature of AP advance approximately 100 °C, beyond what would be expected from each component acting independently. Mechanistic studies demonstrate that Fe2O3@C produced by the decomposition of Fe-based MOF uses the decomposition products of HTPB as a bridge to accelerate the overflow of NH3 on the surface of AP, thereby allowing AP to decompose rapidly at a lower temperature and also accelerating the decomposition of HTPB. Moreover, its influence on the combustion performance of AP-based composite propellants was studied and the combustion rate increased by 20%. This research provides the new directions for designing and applying of Fe-based MOFs materials in HTPB-based solid propellent.

Solids doi: 10.3390/solids6020026

Authors: Anna Michaely Elias C. J. Gießelmann Guido Kickelbick

Partial reduction of transition metal oxides via defect engineering is a promising strategy to enhance their electronic and photocatalytic properties. In this study, we systematically explored the mechanochemical reduction of Nb2O5 using LiBH4 and NaBH4 as reducing agents. Electron paramagnetic resonance (EPR) spectroscopy confirmed a successful partial reduction of the oxide, as seen by the presence of unpaired electrons. Interestingly, larger hydride concentrations did not necessarily enable a higher degree of reduction as large amounts of boron hydrides acted as a buffer material and thus hindered the effective transfer of mechanical energy. Powder X-ray diffraction (PXRD) and 7Li solid-state NMR spectroscopy indicated the intercalation of Li+ into the Nb2O5 lattice. Raman spectroscopy further revealed the increased structural disorder, while optical measurements showed a decreased band gap compared with pristine Nb2O5. The partially reduced samples showed significantly enhanced photocatalytic performance for methylene blue degradation relative to the unmodified oxides.

Solids doi: 10.3390/solids6020025

Authors: Ana-Maria Florea (Raduta) Stefan Caramizoiu Ana-Maria Iordache Stefan-Marian Iordache Bogdan Bita

Opto-spintronics is an emerging field that focuses on harnessing light to manipulate and analyze electron spins to develop next-generation electronic devices. This paper explores recent progress and the role of solid-state materials in opto-spintronics by focusing on key classes of materials, such as ferromagnetic semiconductors, two-dimensional (2D) transition metal dichalcogenides (TMDCs), and topological insulators. It examines the unique properties of ferromagnetic and antiferromagnetic materials and their ability to interact with light to affect spin dynamics, offering potential for improved sensing and quantum computing. By combining opto-spintronics with solid-state systems, spintronic devices could become faster and more efficient, leading to new technological advancements and scalable technologies.

Solids doi: 10.3390/solids6020024

Authors: Mattia Cattelan

The generation of solvated electrons (SEs) from solid-state sources represents a transformative approach to driving challenging reduction reactions under ambient conditions. Diamond, with its almost unique negative electron affinity (NEA) and tunable electronic properties, is emerging as a promising candidate for SE generation in aqueous media. This perspective article reviews the current state of diamond-based SE generators and discusses their potential to catalyze sustainable nitrogen reduction (NRR) to ammonia, carbon dioxide reduction (CO2RR), and the degradation of persistent environmental pollutants. Emphasis is placed on the fundamental processes enabling SE photoinjection from diamond to water, recent experimental breakthroughs, and the prospects for scalable, green applications.

Solids doi: 10.3390/solids6020023

Authors: Sergei A. Kurnosenko Anastasiya I. Ustinova Iana A. Minich Vladimir V. Voytovich Oleg I. Silyukov Dmitrii V. Pankin Olga V. Volina Alina V. Kulagina Irina A. Zvereva

The search for effective and reliable methods of photosensitization of oxide-based semiconductor materials is of great significance for their use in photocatalytic reactions of hydrogen production and environmental remediation under natural sunlight. The present study is focused on partial substitution of titanium with manganese in the structure of layered perovskite-like titanate Na2La2Ti3O10, which was employed to yield a series of photocatalytically active materials, Na2La2MnxTi3−xO10 (x = 0.002–1.0), as well as their protonated forms H2La2MnxTi3−xO10 and nanosheets. It was established that the manganese cations Mn4+ are embedded in the middle sublayer of oxygen octahedra in the perovskite slabs La2MnxTi3−xO102− and that the maximum achievable manganese content x in the products is ≈0.9. The partial cationic substitution in the perovskite sublattice led to a pronounced contraction of the optical band gap from 3.20 to 1.35 eV (depending on x) and, therefore, allowed the corresponding photocatalysts to utilize not only ultraviolet, but also visible and near-infrared light with wavelengths up to ≈920 nm. The materials obtained were tested as photocatalysts of hydrogen evolution from aqueous methanol, and the greatest activity in this reaction was demonstrated by the samples with low manganese contents (x = 0.002–0.01). However, the materials with greater substitution degrees may be of high interest for use in other photocatalytic processes and, especially, in thermophotocatalysis due to their improved ability to absorb the near-infrared part of solar radiation.

Solids doi: 10.3390/solids6020022

Authors: Viktor Markov Talib Farziev Nikita Dybin

This article discusses the superionic glassy GeS2-Sb2S3-AgI system with mobile silver ions as a material for creating new energy-efficient solid-state ion emitters. The effect of replacing silver iodide with germanium sulfide on the structure of the electrolyte, activation energy of diffusion, and specific ionic conductivity was studied. Electrolytes (2.5 + x)GeS2-27.5Sb2S3-(70 − x)AgI, x = 0, 5, 10, 15 were synthesized using the melt-quenching technique in evacuated quartz ampoules. The temperature dependence of conductivity and glass stability parameters (Hruby’s, Weinberg’s and Lu–Liu’s) were determined for them, and the mechanism for increasing glass-forming ability was clarified. It was shown that the presence of iodine in a germanium structural unit is more preferable than in an antimony structural unit; germanium structural units compete for iodine, reducing the number of SbI3 crystallization centers and chain terminations, resulting in additional structural connectivity and stability. It was shown that when silver iodide was replaced by germanium sulfide, the decrease in conductivity due to the reduction in charge carriers was less than expected due to the expansion of the conduction channels.