Journal of the American Ceramic Society最新文献

Hydroxyapatite (HA) ceramics are one of the most widely used biomaterials due to their high biocompatibility and bioactivity. However, the inherent brittleness limits their biomedical applications as load-bearing components for hard tissue repair. Herein, we reported a 127% enhancement in fracture toughness (K_IC increased from 0.62 to 1.41 MPa·m^1/2) of defective Al-doped HA (D-Al-HA) ceramics through defect-engineering mechanism. The theoretical and experimental studies indicated that Al substitution induced lattice distortion and defects such as generation of Ca vacancy, rotation of PO₄³⁻ group, dislocation of Ca ions and disorder of OH⁻ chains. These defects acted as potent Zener pinning sites, suppressing grain boundary mobility during sintering and yielding a refined microstructure. The average grain size decreased from 2.2 µm for HA to 1.3 µm for D-Al-HA ceramics. This grain refinement caused a remarkable increase in fracture toughness of D-Al-HA ceramics through crack deflection, branching, and bridging mechanism. Concurrently, the compressive strength and flexural strength increased by 43% and 21%, achieving 363 ± 86 MPa and 77.4 ± 14.0 MPa, respectively, through Hall‒Petch mechanism. This study not only provided the first insights into the effects of Al-induced defects on the enhanced mechanical performances of HA and the positive role of Al element for HA materials, but also offered a promising pathway for developing stronger and tougher bioceramics for demanding hard tissue implants.

Rare-earth element (REE)-based luminescent materials are widely used in laser and lighting applications, but their sustainability is limited by intensive mining, complex processing, and limited recyclability. Addressing this challenge, we report (for the first time) strong red photoluminescence from highly dense (∼97 ± 1%), phase-pure inverse spinel Mg₂TiO₄ ceramics processed via conventional pressureless sintering. Intense red emissions, mainly originating from self-trapped excitons, were noted in the range of 658–673 nm, indicating strong electron-phonon coupling. The excitation spectra revealed a peak at 485 nm with an optical band gap of 2.56 eV. A variety of sample geometries and sizes consistently exhibited robust and stable red luminescence, without the need for external dopants or rare-earth elements. Photoluminescence and fluorescence lifetime measurements conducted over 25–325 K determined an average lifetime of 0.39 µs at room temperature. Electron paramagnetic resonance spectroscopy analysis further confirmed oxygen vacancy-related defect states, with indications of additional defect centers. Overall, these findings portray Mg₂TiO₄ ceramic as a sustainable and high-performance alternative to REE-based phosphors for red-emitting laser applications.

In this study, density-controlled (DC) alumina components with tailored density gradients were fabricated via direct ink writing (DIW) using bimodal powder mixtures composed of fine and coarse alumina powders. The slurry compositions were systematically adjusted to achieve target density distributions, and the resulting print quality and mechanical performance—particularly bending strength—were thoroughly evaluated. Distortion at the interfaces between regions of different densities was observed, primarily due to slurry inflow into gaps between previously deposited filaments and the substrate. DC alumina specimens with a significant internal density contrast exhibited edge-initiated interfacial cracking, attributed to tensile stresses induced by differential shrinkage. The magnitude of these internal stresses exceeded the calculated material strength by a factor of 1.89, leading to failure. Finite element analysis was employed to investigate the stress distribution and to assess the impact of shrinkage mismatch on structural integrity. Notably, certain density configurations yielded higher bending strength than their uniformly dense counterparts, while others showed comparable performance. These results demonstrate both the potential of controlling internal density to tailor mechanical properties and the key challenges associated with multimaterial DIW of ceramics, particularly in managing interfacial stress concentrations and shrinkage-induced defects.

Hafnia has become a promising thermal protective material due to its low thermal conductivity and high mechanical strength. However, it is difficult to balance the densification and grain growth of the material with the traditional sintering technology. In this study, HfO₂ ceramics with high-density (97.4%), ultra-fine grain size (149 nm), enhanced mechanical properties of hardness (12.23 GPa), and fracture toughness (3.00 MPa m^1/2), low thermal conductivity (3.75 W m⁻¹ K⁻¹) and excellent ablation-resistant properties were prepared under a high pressure (200 MPa) and a low temperature (1350°C) by spark plasma sintering (SPS) from nanocrystalline raw power (77.4 nm). According to calculation, the relative density could reach up to78.9% after the contribution of plastic deformation under high pressure of 200 MPa at 1350°C without thermal diffusion. The high pressure induced high-density lattice distortions such as lamination faults and twins in HfO₂ ceramics. These lattice distortions contributed to high mechanical strength and low thermal conductivity.

Agglomerations of carbon-based inclusions and the low adhesion of inclusion-matrix interfaces are commonly viewed as detrimental to the strength and fracture toughness of ceramic composites. While large, high-power agglomerations indeed promote microcracking, our computations show that moderate agglomeration levels can enhance energy dissipation through Y-junctions in inclusion networks.

Focusing on high-temperature Zr-based reduced graphene oxide/ceramic nanocomposites, we use a polytopal cell complex (PCC) framework to analyze macrocrack bridging for 12 graphene precursor powders with distinct log-normal size distributions. The simulations quantify how inclusion fraction, strip-length statistics, and agglomeration power jointly determine the topology of percolation networks and their contribution to fracture resistance.

The results rationalize experimental observations that uniform-size precursor powders reduce harmful clustering while maximizing bridging. Dislocation-based estimates indicate that, even under ideal architectures, crack-bridging toughening is theoretically limited to a factor of 2–3, exceeding but consistent with the 30%–50% improvements typically reported.

Phase equilibria in the Li₂O‒MnO_x system was experimentally investigated under air condition and inert atmosphere (Ar). The experimental investigations for selected compositions of isothermally heat-treated samples were performed using X-ray diffraction and scanning electron microscopy/energy dispersive X-ray spectroscopy. Differential thermal analysis was used to determine the temperature of phase transformations. The thermodynamic parameters were optimized using the CALPHAD approach. Homogeneity ranges for cubic and tetragonal phases were reproduced and modeled in the framework of the compound energy formalism, while LiMnO₂ and Li₂MnO₃ phases were treated as stoichiometric. Two-sublattice partially ionic liquid model was employed to describe the liquid. Available thermodynamic properties were accounted during the optimization and the results reproduce them well. The calculated phase diagram agrees with the experimental data and it reproduces the equilibria within uncertainties.

Texture engineering stands as a pivotal strategy for enhancing the performance of lead-free piezoelectric ceramics. The degree of texture (F₀₀₁), a paramount parameter governing electromechanical properties, is critically dependent on the concentration of anisotropic templates. This study presents a systematic investigation into the influence of BaTiO₃ (BT) template content on the microstructure evolution and functional properties of [0 0 1]_c-textured (Ba_0.99Ca_0.01)(Ti_0.98Zr_0.02)O₃ (BCTZ) ceramics fabricated via templated grain growth (TGG). Our findings reveal a non-monotonic relationship: at lower concentrations, BT templates facilitate epitaxial growth, leading to a concomitant increase in F₀₀₁, piezoelectric coefficient (d₃₃), and electromechanical coupling factor (k_p). However, beyond an optimal threshold, excessive templates induce stoichiometric deviations, microstructural heterogeneity, and performance degradation. The optimal composition, BCZT with 3 mol% BT templates, achieves an exceptional texture degree of 97% and a superior d₃₃ of 591 pC/N, significantly outperforming its randomly oriented counterpart. Furthermore, synergized with phase boundary engineering, this composition exhibits remarkable thermal stability (<18% strain variation over 20–100°C) and a high output power density of 7.8 µW/mm³ under an acceleration of 10 m/s². These outstanding properties underscore the great potential of textured BCZT ceramics for high-stability piezoelectric applications.

This study presents the first systematic experimental determination of phase equilibria in the Er₂O₃–Al₂O₃–SiO₂ system at 1600°C in air, employing the high-temperature isothermal equilibration method followed by rapid drop-quenching to preserve high-temperature phase assemblages. The mineralogy and chemical compositions of the equilibrated samples were analyzed by x-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe x-ray microanalysis (EPMA). One single liquid equilibria, five two-phase equilibria (liquid–SiO₂, liquid–Er₂Si₂O₇, liquid–Er₃Al₅O₁₂, liquid–Al₂O₃, and liquid–mullite) and seven three-phase equilibria (liquid–SiO₂–Er₂Si₂O₇, liquid–Er₂Si₂O₇–Er₂SiO₅, liquid–Er₂SiO₅–Er₃Al₅O₁₂, liquid–Er₃Al₅O₁₂–Al₂O₃, liquid–Al₂O₃–mullite, Er₂O₃–Er₂SiO₅–Er₄Al₂O₉, Er₃Al₅O₁₂–Er₂SiO₅–Er₄Al₂O₉) were observed in the equilibrium ternary system. The 1600°C isothermal section of the Er₂O₃–Al₂O₃–SiO₂ phase diagram in air (pO₂ = 0.21 atm) was constructed based on the present experimentally determined equilibrium phase compositions. The liquid area and the primary fields of SiO₂, Er₂Si₂O₇, Er₃Al₅O₁₂, Al₂O₃, and mullite were constructed. The comparison of the present experimental results deviate significantly from the modelling by FactSage (version 8.3) using its “FactPS” and “FToxid” databases, suggesting that FactSage underestimated the stability of the liquid phase under the present experimental conductions.

Brittle oxides, such as α-Al₂O₃, i.e., sapphire, are traditionally unsuitable for ductile applications, yet exhibit enhanced plasticity at nanoscale. This study explores the mechanical behavior of c-plane-oriented, dislocation-free monocrystalline α-Al₂O₃ via molecular dynamics (MD) simulations and experiments, including nanoindentation and post-indentation TEM analysis. The results demonstrate high strength with homogeneous, extensive deformation without failure. Plasticity is dominated by basal (0001) dislocations and rhombohedral [10$�\overline{1}$2] twins, which nucleate at deformation onset, as confirmed by MD and TEM. Generalized stacking fault energy (GSFE) and twinning fault energy (TFE) calculations elucidate mechanisms that mitigate crack initiation and propagation on the c-plane, aligning simulations with observations. These insights advance the understanding of nanoscale ductility in oxides, broadening the utility of sapphire in load-bearing micro/nano devices.

This study presents a novel process for the synthesis of MoO₂ and Mo₂C particles. It consisted of waste polyethylene (PE) pyrolysis and MoO₃ reaction with pyrolytic gas in a furnace with two-independently controlled zones. The gaseous species such as H₂ and CH₄ were in situ generated from the waste during heating to the temperatures ranging from 670 to 800 K. The resultant pyrolytic gas was carried to the MoO₃ powder bed by Ar flow to obtain MoO₂ at 900 K. Mo₂C was synthesized in the temperature range 1000–1300 K by the reaction of pre-reduced MoO₂ with the pyrolytic gas. Mo₄O₁₁, MoO₂, and Mo₂C phases sequentially formed during the reduction and carburization of the MoO₃ powder. Mo₄O₁₁ phase played an intermediate role in the reduction, as predicted by the thermodynamics. MoO₂ and Mo₂C phases were obtained at PE/oxide reactant ratios higher than those predicted. The discrepancy was discussed in terms of essential characteristics of the thermodynamics and the experiments. Mo₂C powders consisted of fine platelet-shaped crystals similar to those of MoO₂. Mo₂C crystallite size decreased, whereas microstrain increased as the carburization temperature decreased. This study demonstrates that waste PE can be recycled as alternative H₂ and C resources in reduction/carburization processes.