Journal of the American Ceramic Society最新文献

This study pioneers the cross-disciplinary application of garnet-type solid-state electrolyte Li₇La₃Zr₂O₁₂ (LLZO) in microwave dielectric ceramics. LLZO was synthesized via solid-state reaction, achieving optimized microwave dielectric properties at 900°C: ε_r = 8.13, Q × f = 31 735 GHz, τ_f = −44.3 ppm/°C. Direct cofiring experiments with Ag electrodes validated its compatibility with low-temperature cofired ceramic (LTCC). X-ray diffractometer (XRD)/scanning electron microscope (SEM)–energy-dispersive X-ray spectroscopy (EDS) confirmed interfacial stability and chemical inertness, overriding standalone thermal expansion parameter considerations. A Beidou antenna prototype on LLZO substrates demonstrated 59.2 MHz bandwidth at 1.57 GHz with 4.33 dBi gain and >97% radiation efficiency. By synergizing low-loss microwave response with inherent Li⁺ conductivity and thermal robustness, LLZO emerges as a multifunctional platform for integrated energy-communication systems. It enables future designs of LTCC based self-powered modules and real-time structural health monitoring devices. This work bridges solid-state electrolytes and microwave ceramics, offering a paradigm for material innovation in fifth-generation (5G)/sixth-generation (6G) networks and intelligent electronics.

The thermodynamic stability of six distinct compositions within the Zr—Ta—C ternary system is investigated in this study, marking the first report of their synthesis through carbothermic reduction in vacuum. A prolonged annealing process at 2200°C enabled high densification and phase equilibrium. Detailed phase identification and microstructural characterization through microscopy and X-ray diffraction techniques revealed clear compositional trends and stable phase formations. Two compositions ((Ta_0.2Zr_0.8)C_0.6 and (Ta_0.5Zr_0.5)C₁) were selected for ion irradiation experiments using 200 keV Kr⁺ at 600°C—representing the first-ever irradiation study on the Zr—Ta—C system. The findings indicated defect accumulation and nanoscale cavity formation without any evidence of amorphization, highlighting the system's structural stability under irradiation. Together, the synthesis and irradiation results provide a basis for further investigation of the system and suggest its relevance for applications under extreme environments.

Dislocations in oxides with ionic/covalent bonding hold potential for harnessing versatile functionalities. Here, high-density dislocations in a large plastic zone in potassium niobate (KNbO₃) crystals are mechanically introduced by room-temperature cyclic scratching to enhance piezocatalytic hydrogen production. Unlike conventional energy-intensive, time-consuming deformation at high temperature, this approach merits efficient dislocation engineering. These dislocations induce local strain and modify the electronic environment, thereby improving surface reactivity and charge separation, which are critical for piezocatalysis. This proof-of-concept offers a practical and sustainable alternative for functionalizing piezoelectric ceramics. Our findings demonstrate that surface-engineered dislocations can effectively improve the piezocatalysis, paving the way for efficient and scalable piezocatalytic applications.

Multilayer ceramic capacitors (MLCCs) face the threat of failure due to various electrical stresses during long-term use. This study systematically investigates the mechanisms of breakdown failure in MLCCs under impulse voltage, ramped voltage, and endurance voltage, using a combination of experimental characterization and finite element method simulations. The distributions of the electric field, mechanical stress field, and thermal effects within MLCCs were comprehensively analyzed. As the duration of voltage application increases, the breakdown voltage of MLCCs decreases. All electrical stress-induced failures occur at the edge regions with inferior electrode quality, where severe localized electric field concentration is present. The failure mechanism induced by short-duration, high-voltage impulse stress is electromechanical breakdown, which tends to occur at the L-direction edges where mechanical stress is more concentrated. In contrast, the failure mechanisms induced by longer-duration, lower-voltage ramped voltage and endurance voltage are electrothermal breakdown, preferentially initiating at the W-direction edges, where heat accumulation is more pronounced due to poorer thermal dissipation. The findings of this study provide a theoretical reference for a deeper understanding of the failure behavior of MLCCs under electrical stress and for improving their electrical reliability.

In recent years, the digital light processing (DLP) technology has demonstrated tremendous potential in the field of silica glass manufacturing. However, the size of glass components produced is usually only a few millimeters due to the fact that large-sized glass components are prone to cracking during the manufacturing process, especially induced by the thermal degradation of cured resin during the debinding process. This study elaborates in detail on the effect of polymerization degree on debinding induced cracking in 3D printed silica glasses. Specifically, green parts cured by a DLP 3D printer with photosensitive resin containing silica nanoparticles were manufactured under different silica particle loadings, light intensities, and exposure time. The results indicate that the polymerization degree decreases with increasing silica loading, while increases with increasing light intensities and exposure times. The higher polymerization degrees led to serious cracking. These findings are crucial for optimizing the quality and structural integrity of 3D printed silica glass components.

In this study, a series of (1-x)Sr_0.5Zr₂(PO₄)₃-x(Ce_1-2yNd_ySm_y)PO₄ (abbreviated as SrZP-(Ce, Nd, Sm)PO₄, x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1; y = 0, 1/12, 2/12, 3/12, 4/12, 5/12, 6/12) dual-phase ceramic waste forms were fabricated through a one-step microwave sintering technique. The phase evolution, micromorphology, and densification behavior of these ceramics were systematically investigated using XRD, Raman spectroscopy, SEM-EDS, and density measurement. The results confirmed that the dual-phase ceramics exclusively consisted of SrZP and (Ce, Nd, Sm)PO₄ phases, which coexisted stably and independently, enabling simultaneously effective immobilization of simulated fission products (Sr²⁺) and actinides radionuclides (Ce³⁺, Nd³⁺, and Sm³⁺). The ceramics exhibited a homogeneous distribution of both phases, a compact micromorphology, and relative densities achieving a maximum of 98.9%. It was demonstrated that alterations in the phase content (x value) induced only negligible variations in the lattice parameters of both crystalline phases, indicating minimal structural perturbations. Rietveld refinement analysis revealed a gradual reduction in the lattice parameters of the (Ce, Nd, Sm)PO₄ phase with increasing y value, consistent with the anticipated immobilization of the simulated actinide radionuclides. In addition, by integrating XRD and Raman analyses, the temperature-induced phase evolution of the representative sample SrZP-Ce_1/3Nd_1/3Sm_1/3PO₄ was comprehensively characterized. The results indicated that the Ce_1/3Nd_1/3Sm_1/3PO₄ phase preferentially formed over the SrZP phase during the dual-phase ceramic preparation. Furthermore, the Kissinger model based on TG-DSC results at various heating rates (β_T = 10, 15, 20, and 25 K/min) provided additional thermodynamic evidence, in which the Ce_1/3Nd_1/3Sm_1/3PO₄ phase possessed a lower apparent activation energy (353.35 kJ/mol) than the SrZP phase (501.33 kJ/mol). Besides, the SrZP-Ce_1/3Nd_1/3Sm_1/3PO₄ dual-phase ceramic waste form demonstrated high chemical stability, with normalized leaching rates of all elements remaining relatively low (LR_Sr∼10⁻⁴ g·m⁻²·d⁻¹, LR_Ce∼10⁻⁷ g·m⁻²·d⁻¹, LR_Nd∼10⁻⁷ g·m⁻²·d⁻¹, and LR_Sm∼10⁻⁶ g·m⁻²·d⁻¹).

High-strength α-Al₂O₃ porous ceramics are highly valuable for applications in aerospace, chemical catalysis, and related fields due to their exceptional mechanical properties and chemical stability. However, their development has been hindered by performance degradation and high energy consumption associated with traditional high-temperature sintering methods. While the cold sintering process (CSP) can effectively address these challenges, research on fabricating phase-pure α-Al₂O₃ via CSP remains limited. In this work, α-Al₂O₃ porous ceramics were prepared from hydratable alumina by CSP without sintering aids and post-processing. The hydration characteristics of ρ-Al₂O₃ were exploited to optimize the distribution of the transient liquid phase within the system, and the existence of vapor pressure was detected. The influence of CSP parameters on the phase composition, microstructure, and mechanical properties of the samples were systematically investigated. The obtained porous ceramics exhibited a porosity of 42.3%‒34.4%, an average pore size of 463.6 nm, a compressive strength of 89.4‒140.2 MPa, a thermal conductivity ranging from 12.7 to 2.2 W/(m·K) from room temperature to 1200°C, and withstood sintering temperatures up to 1300°C. The study elucidated the nucleation of boehmite and its phase transformation to α-Al₂O₃ within the hydrothermal framework, a mechanism supported by direct experimental evidence of the vapor pressure generated in situ. This finding offers significant scientific implications for advancing CSP in the fabrication of α-Al₂O₃ porous ceramics.

This study aims to reveal the immobilization mechanism of Nd(III) during the in situ formation of C–S–H. The experimental results indicate that during the formation of C–S–H, Nd was incorporated into its dreierketten silicate chain as Nd tetrahedra via substituting Si tetrahedra at the Q^2b site, which exhibited the lowest defect formation energy according to simulation, resulting in the formation of calcium neodymate silicate hydrates (C–Nd–S–H). These results are highly comparable to density functional theory calculations. The incorporation of Nd into C–Nd–S–H resulted in the elongation of silicate chains, an increase in the inter-layer space and Q² proportion, and local enrichment of Nd without altering the tobermorite-like structure. The immobilization efficiency of C–S–H for Nd reached 99.99% during synthesis.

The disposal of high-level waste, particularly the management of long-lived actinides after immobilization, requires a thorough assessment of the long-term stability of nuclear waste forms in underground repositories. In this work, the garnet Ca_1.5Nd_1.5Zr_1.5Fe_3.5O₁₂ was successfully synthesized via high-temperature solid-phase sintering at 1300°C, exhibiting excellent phase purity and microstructural integrity. The chemical stability of the garnet waste form was evaluated under various conditions, including acidic, alkaline, saline, oxidizing environments, and deionized water. Both static and semi-dynamic leaching methods were employed to investigate the leaching mechanisms in different solutions. In acidic leachate, the normalized leaching rate initially increased before decreasing, as the dominant leaching mechanism shifted from slow dissolution and surface reactions to long-term diffusion. In the other four conditions, surface dissolution and internal diffusion processes primarily controlled the leaching mechanism. Ca_1.5Nd_1.5Zr_1.5Fe_3.5O₁₂ demonstrated outstanding thermal stability and corrosion resistance, positioning it as a promising candidate for the immobilization of actinide nuclear waste.

A series of (Y, Yb, Zr, Hf, Sn, W)O_2−δ high-entropy ceramics with varying mole fraction of main elements were synthesized for the first time through the solid-state reaction synthesis method. The microstructure, phase composition, and properties of the prepared materials were thoroughly analyzed and tested. The results indicate that the phase composition transformed from a single-phase fluorite structure to a single-phase C-type rare earth sesquioxide structure as the mole fraction of +3 cations increases. The thermal conductivity of the prepared high-entropy ceramics with porosity of 49.8%–50.1% is very low ranging from 0.33 to 0.37 W·m⁻¹·K⁻¹. Among them, the single-phase C-type rare earth sesquioxide with a higher oxygen vacancy concentration was employed as a catalyst in the CO₂ hydrogenation reaction, attaining a high CO₂ conversion rate of 82.0%. The obtained results have deepened understanding of the role of oxygen vacancies and have important guiding significance for the study of high-entropy oxides with fluorite derived structures.