Journal of the American Ceramic Society最新文献

A new family of rare-earth fluoroborates, Ba₅Ln₃(BO₃)₆F (Ln = Pr, Nd, Sm, Eu, Gd, and Dy), has been synthesised via a conventional solid-state route and systematically investigated as potential luminescent host materials. Structural analyses reveal that the compounds adopt a monoclinic framework structure of isolated BO₃ units, with lattice contraction observed across the lanthanide series. The fluoroborates exhibit wide optical band gaps (3.84–5.62 eV) and excellent thermal stability, making them suitable hosts for rare-earth activation. Among the investigated compositions, Eu³⁺-activated Ba₅Gd_3-xEu_x(BO₃)₆F displays intense red emission under both near-ultraviolet (near-UV) (394 nm) and blue (465 nm) excitation. The dominant ⁵D₀→⁷F₂ transition and resolved Stark splitting indicate that Eu³⁺ occupies a low-symmetry, non-centrosymmetric environment within the fluoroborate lattice. The emission intensity reaches a maximum at x = 0.7, beyond which concentration quenching occurs through multipolar interactions as the quenching pathway. Furthermore, the phosphor exhibits deep-red chromaticity coordinates and a high color purity of approximately 93%. The combination of structural robustness, strong excitation in the near-UV/blue spectral region, and high-quality red emission highlights Ba₅Gd_3-xEu_x(BO₃)₆F as a promising fluoroborate phosphor for solid-state lighting applications.

The current work presents the structural, optoelectronic, hydrogen (H₂) storage, and mechanical features of novel cubic hydrides XCa₃H₉ (X = P, As, Sb). The negative formation energies and AIMD simulations confirm that the studied materials are thermodynamically stable. The materials demonstrate gravimetric storage capacities (C_wt%) of PCa₃H₉ (5.66 wt%), AsCa₃H₉ (4.44 wt%), and SbCa₃H₉ (3.61 wt%), suggesting higher capacity for PCa₃H₉ exceeding DOE's goal of 5.5 wt%. Additionally, PCa₃H₉ demonstrates the highest volumetric capacity of 109.1 g.H₂/L compared to AsCa₃H₉ (106 g.H₂/L) and SbCa₃H₉ (98.4 g.H₂/L). The desorption temperatures are 348.8, 319.1, and 333.9 K for PCa₃H₉, AsCa₃H₉, and SbCa₃H₉, respectively. Mechanical evaluations have been performed to analyze the ductility or brittleness, melting points, Debye temperature, and phase stability under stress. Electronic band structures of XCa₃H₉ (X = P, As, Sb) validate the metallic nature of PCa₃H₉, which varies to semiconductor characteristics for AsCa₃H₉ and SbCa₃H₉, with indirect narrow band gaps of 0.28 and 0.88 eV according to Tran–Blaha-modified Becke–Johnson (TB-mBJ) calculations. The optical characteristics offer insights into absorption, energy dissipation, light transmission, and reflection, suggesting optoelectronic potential. These perovskite hydrides have elevated absorption coefficients (∼10⁵ cm⁻¹), indicating their potential for energy harvesting applications. Collectively, the analyzed results emphasize that PCa₃H₉ is a more beneficial material for applications involving H₂ storage.

Aliovalent Na-substituted calcium ferrite photocathode films with Ca_1-xNa_xFe₂O₄ (x = 0, 0.02, 0.04, 0.06, 0.08) composition were fabricated on fluorine-doped tin oxide (FTO) coated glass substrates via a facile drop-casting method followed by thermal annealing. Powder x-ray diffraction (XRD) combined with Rietveld refinement confirmed the formation of single-phase orthorhombic CaFe₂O₄ with a Pnma space group for all compositions, while systematic lattice expansion suggested the successful incorporation of Na into the CaFe₂O₄ framework. Field-emission scanning electron microscopy (FESEM) revealed that Na substitution promoted grain growth and improved film connectivity compared with pristine CaFe₂O₄. Optical absorption spectra demonstrated a gradual bandgap narrowing from 2.20 to 1.90 eV with increasing Na content, accompanied by enhanced visible-light absorption. Photoelectrochemical measurements revealed cathodic photocurrent responses characteristic of p-type semiconductor behavior. The optimized Ca_0.94Na_0.06Fe₂O₄ photocathode achieved the highest photocurrent density of −192.6 µA cm⁻² at 0.2 V vs. RHE, representing a 3.4-fold enhancement compared with pristine CaFe₂O₄, together with an onset potential of 0.88 V vs. RHE. Mott–Schottky and impedance analyses indicated increased acceptor density and reduced charge-transfer resistance after Na incorporation. These improvements are attributed to Na-induced electronic structure modulation and defect-mediated charge compensation, facilitating carrier transport and interfacial charge-transfer kinetics.

High-entropy carbides (HECs) are promising ultra-high-temperature ceramics but suffer from poor sinterability, residual stress, and grain boundary defects. Conventional hot pressing (HP) cannot simultaneously achieve full densification and homogeneous lattice strain. We report a strain-engineering strategy using oscillatory pressure sintering (OPS) at 1800°C to prepare (Zr,Mo,Ti,Nb,Ta)C with low-strain grain boundaries. OPS yields near-full densification (99.64%), uniform elemental distribution, and a strain range of −1.5% to +1.5%, narrower than HP (−9% to +15%), eliminating stress concentration. The microstructure exhibits hardness of 25.18±0.38 GPa and toughness of 3.54±0.23 MPa·m^1/2. OPS homogenizes lattice strain, stabilizes grain boundaries, and enhances properties, offering a route to high-performance HECs.

Controlling the surface pyrolysis of ceramic powders during high-temperature plasma spraying is a critical challenge for producing phase-pure and structurally integral coatings. Here we show that adding He to the conventional Ar+H₂ plasma working gas effectively suppresses the in-flight surface pyrolysis of ZrSiO₄ particles while maintaining adequate melting for deposition. By combining CFD simulations, optical emission spectroscopy (OES), and coating microstructure analysis, we demonstrate that He addition induces a synergistic “mild cooling and velocity enhancement” effect. As the He volume fraction increases from 0 to 30 vol.%, the electron excitation temperature decreases linearly from 14 202 to 12 412 K, while the maximum jet velocity rises from 940 to 1271 m/s. This shortens the residence time of particles in the high-temperature zone and reduces the surface pyrolysis conversion rate from 42.5% to only 12.3% at the optimal He content of 10 vol.%. Excessive He addition (≥30 vol.%) leads to incomplete melting and formation of monoclinic ZrO₂, degrading coating integrity. This work establishes a quantitative relationship among gas composition, particle in-flight behavior, and coating phase composition and microstructure, providing a surface-engineering strategy for plasma processing of high-temperature ceramic powders.

The incorporation of TiB₂ into B₄C ceramics is considered an effective route to enhance the toughness and strength, yet the effect in rate dependence across a wide range of strain rates remains unclear. This study investigates the mechanical behavior of B₄C and TiB₂–B₄C (TBC) under quasi-static, dynamic, and high-velocity impact. The results indicated that TBC exhibited a steeper compressive stress–strain-rate response at $�\dot{\epsilon }$ = 650–1350 s⁻¹ and a higher tensile strain-rate sensitivity coefficient (1.99) at $�\stackrel{.}{\epsilon }$ = 0–155 s⁻¹. Voronoi simulations revealed that the TiB₂/B₄C interface provided additional potential crack initiation sites, resulting in the average number of cracks increasing by 33.1%. Under high-velocity impact, a high-density damage zone formed by the refinement of TBC fragments caused lateral deflection of the projectile. The impact performance advantage of TBC stemmed from high thickness utilization efficiency (+17.3%). Furthermore, the comprehensive impact resistance index was 7.26% higher than that of B₄C.

The development of leakage-free and thermally reliable phase change materials (PCMs) is crucial for efficient thermal energy storage applications. In this study, a form-stable PCM composite was engineered using a hybrid porous matrix composed of montmorillonite-rich bentonite, kaolin, and perlite in an optimized 1:1:2 ratio, combined with a small amount (2 wt%) of expanded graphite to enhance thermal conductivity. Capric acid (CA) was incorporated via melt infiltration, and PCM loadings from 20 to 50 wt% were investigated. Although the 50 wt% composite exhibited a high latent heat of approximately 77 J g⁻¹, quantitative leakage testing revealed measurable PCM migration at this loading. In contrast, the optimized 35 wt% composite showed no detectable leakage under the applied test conditions, together with a latent heat of approximately 53 J g⁻¹ and superior mechanical integrity. Structural and physicochemical analyses confirm physical confinement of CA within the hierarchical pore network without chemical interaction. These results demonstrate that synergistic integration of multi-clay porous matrices with a minimal conductive additive provides a simple and potentially scalable approach for developing form-stable PCM composites for thermal energy storage applications.