Solids

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. Full article

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, [Cu_3−x(As_1−ySb_y) (Cu₃P-type; hP24, P6₃cm) and Cu_3−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. Full article

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. Full article

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. Full article

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. Full article

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) ų. 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 ${\displaystyle \genfrac{}{}{0pt}{}{1}{\infty }}[$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. Full article

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. Full article

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. Full article

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. Full article

Poly(vinyl alcohol) (PVA)/montmorillonite (MMT)/Ti₃C₂T_x (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. Full article

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. Full article

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. Full article

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. Full article

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/SnO_x matrix. These findings provide insights into the non-equilibrium oxidation dynamics of tin and the formation of metastable SnO_x phases during pulsed laser deposition. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article