International Journal of Applied Ceramic Technology最新文献

The mechanism of the reliability improvement by alloying Ni internal electrodes of BaTiO₃-based multilayer ceramic capacitors (MLCCs) was studied from two perspectives: electric barrier formation at the electrode-dielectric interface and diffusion of alloying elements into the bulk dielectric layer. In the case of Ni-Sn alloy electrodes, the reliability improvement is due to the formation of a Sn segregation layer at the interface between the internal electrode and the dielectric layer, and the associated formation of a Schottky barrier, which is an electron barrier layer. Therefore, when the dielectric layer is sufficiently thin, this electron barrier layer functions critically, but as the dielectric film thickness increases, the effect of this barrier layer gradually decreases because of an increased number of grain boundaries and the grains in the dielectric layer, which are other factors that determine the insulation. On the other hand, in the case of Ni-In alloy electrodes, In diffuses not only at the interface between the internal electrode and the dielectric, but also into the shell part of the “core-shell” structure of the BaTiO₃ grains in the dielectric layer along with the grain boundaries. Therefore, it was revealed that the reliability improvement continues even if the dielectric thickness increases to a certain extent. The outstanding improvement in the reliability of the Ni–In MLCC could be derived from not only the formation of an electrical barrier at the interface between the internal electrode and the dielectric layer, but also enhanced resistivity provided by a grain boundary barrier layer and an intragranular acceptor region at the shell region of the core-shell structure by the In diffusion.

Regulatory agencies and key stakeholders are increasingly promoting the use of probabilistic approaches in design processes for large corporations. This shift is particularly emphasized in analyzing mechanical properties, such as fatigue and failure prediction. Additionally, the use of probabilistic artificial intelligence represents a transformative advancement in material science that leads to enhanced predictive accuracy and robust decision-making capabilities. These artificial intelligence methods enable more informed decision-making in the design and evaluation of advanced materials by quantifying uncertainty and offering probabilistic assessments, particularly for applications involving extreme environments. High-temperature materials, such as carbon/carbon (C/C) composites, are essential for modern technological applications. However, their vulnerability to oxidation poses a significant barrier, indicating the necessity for effective protective coatings. The application of these coatings to C/C composites is complex and has hindered their widespread use in high-temperature settings. In this study, we utilize finite element analysis (FEA) and machine learning (ML) combined with Bayesian probability to examine the behavior of silicon carbide ceramic-coated cubic C/C composites. The investigation focuses on how stress and strain evolve under varying thermal conditions and cyclic thermal loading from a probabilistic perspective. This work integrates FEA and Bayesian probabilistic-based ML to enhance the predictive power for evaluating ultra-high-temperature materials.

Lithium lanthanum titanate (Li_0.33La_0.56TiO₃, LLTO) solid electrolyte exhibits excellent Li⁺ ionic conductivity with high conductivity at room temperature. However, its relatively high grain boundary resistance results in a lower overall ionic conductivity in practical applications (10⁻⁵–10⁻⁶ S·cm⁻¹). To improve the total ionic conductivity, the LLTO solid electrolyte was synthesized by introducing Sb³⁺ with a large ionic radius to dope Ti⁴⁺ by the solid phase method, and the effects of different doping amounts on the structure and properties of the LLTO solid electrolyte were studied. It was found that when the doping content was low, Sb³⁺ could promote the growth of grains and increase the density, which was conducive to the conduction of Li⁺ ions. However, excessive doping will change the morphology of the grains, resulting in a decrease in density, which is not conducive to the improvement of ionic conductivity. The total ionic conductivity of the undoped samples in this study is 0.82 × 10⁻⁵ S·cm⁻¹. When the doping content is 0.03 mol, the activation energy decreases to 0.243 eV, the maximum bulk density reaches 5.557 g/cm³, and the optimal ionic conductivity increases significantly to 4.55×10⁻⁵ S·cm⁻¹, showing a substantial improvement compared with the undoped sample.

The combination of silicon carbide (SiC) and silicon dioxide (SiO₂) holds significant potential for advancing modern technologies, particularly the development of microwave-absorbing materials (MAMs) due to their unique dielectric properties. In this study, a simple and cost-effective method has been used to synthesize SiC–SiO₂ nanocomposites from silicon and graphite powders using high-energy milling at room temperature in air atmosphere, without any heat treatment. X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and high-magnification transmission electron microscopy characterizations confirmed the formation of pure SiC–SiO₂ nanocomposites after milling for 20 h, with particle sizes reduced to sub-100 nm. Vector network analyzer measurement revealed the composites’ enhancement in microwave absorption performance at a thickness of only 1.50 mm from a minimum reflection loss (RL) of ‒4.00 dB at 10.88 GHz (∼60% absorption) before milling to ‒12.15 dB at 11.50 GHz (∼93% absorption) after 20 h of milling, with further improvement to ‒13.80 dB at 11.50 GHz (∼96% absorption) after 40 h. The effective absorption bandwidth is also enhanced from 0.84 to 1.54 GHz after 20 and 40 h of milling, respectively. The enhanced microwave absorption is attributed to the nano-size effect, interfacial polarization, and multiple internal reflection. These findings may pave the way for realizing the industrial-scale production of SiC-based MAMs.

Photocatalysis presents a promising solution for environmental remediation, though conventional photocatalysts remain constrained to the ultraviolet and partially visible regions of the solar spectrum. To address this limitation, we developed a NaYF₄:Yb,Er/BiOBr (N/B) composite photocatalyst, leveraging upconversion luminescence to convert near-infrared photons into visible light while utilizing BiOBr's narrow bandgap for enhanced visible-light absorption. The composite photocatalyst was fabricated via a two-step solvothermal approach and evaluated for the degradation of methyl orange (MO). Remarkably, the N/B-120°C sample demonstrated superior photocatalytic activity, achieving degradation rates 2.4- and 5.4-fold higher than those of pristine BiOBr and commercial TiO₂ (P25), respectively. This enhanced performance is attributed to synergistic effects including an increased specific surface area (23.96 m²/g for N/B-120°C vs. 16.28 m²/g for BiOBr), reduced charge transfer resistance (as evidenced by electrochemical impedance spectroscopy (EIS) Nyquist plots), elevated oxygen vacancy concentration (as verified by x-ray photoelectron spectroscopy [XPS]), and extended solar spectral utilization range (400–980 nm). This work presents a viable strategy to improve the efficiency of photocatalysis.

The deposition of a 2.0 µm SiO₂ film on the alumina surface in Kovar^TM/94% alumina joints enables the formation of a silicide reaction layer on the alumina during brazing with 97Ag2Zr1Cu. Additionally, the average and standard deviation of joint thickness decrease from 50 to 15 and 29 to 4 µm, respectively compared to joints without added SiO₂. Finally, the average failure stress of these braze joints was 45 MPa, while that of similar joints without added SiO₂ was 90 MPa. Sessile drop experiments of 98Ag2Zr on SiO₂ and 99.6% Al₂O₃ substrates show that the braze wets and spreads to 3x its original area on SiO₂ with a wetting angle near 0°, but remains the same area on 99.6% Al₂O₃ with a wetting angle of 106.6°. Focused-ion-beam scanning electron microscopy analysis of a cross-section of the 98Ag2Zr sessile drop on the SiO₂ substrate has shown that Zr reacts with SiO₂ to form Zr oxide and silicide layers. Scanning transmission electron microscopy diffraction and energy dispersive X-ray spectroscopy analysis indicate this silicide layer contains tetragonal Zr₅Si₄. Analysis shows the silicide layer enhances wetting and joint uniformity while unreacted SiO₂ embrittles the joint and degrades strength.

The ceramic tile industry is energy intensive, characterized by long firing times and high temperatures. Therefore, flash sintering (FS), which greatly conserves energy by completing sintering in a few seconds at low temperature, is of interest to this industry. In this study, FS was applied for the first time to ceramic wall tile bodies. The experiments were carried out at a furnace temperature of 900°C, under an applied field of 100 V/cm, and current densities of 50, 100, 150, and 200 mA/mm². The influence of process parameters on phase and microstructure development, and water absorption and hardness properties were investigated. These results are compared to the traditional industrial/conventional process (CP). It was observed that the reactions among the raw materials were completed in a few seconds during flash. The microstructure was similar to the CP specimens. Water absorption (9.55%–10.32%), porosity (19.06%–23.92%), and bulk density (1.94–2 g/cm³) values were also found to be comparable. The bulk density increased and porosity decreased with higher current density. Besides quartz and anorthite, gehlenite phase was also detected in FS samples, which was absent in CP specimens. The hardness of the FS samples was approximately 25% lower than CP samples.

Creep rates of polycrystalline yttrium–aluminum garnet (Y₃Al₅O₁₂, YAG) and lutetium–aluminum garnet (Lu₃Al₅O₁₂, LuAG) under 50 to 200 MPa compressive stress were measured at 1300°C in air and in steam. Measurements for 2% Er and 2% Yb doped YAG were also done at 1300°C, and for YAG at 1400°C. The effect of 0.3 to 8 µm grain size variation on creep rate was determined. Flow stress exponents for all materials were determined, and the creep rate activation energy for YAG was determined. Creep rates in steam were slightly faster than those in air. Er and Yb dopants in YAG had little discernible effect on creep rates. LuAG creep rates, adjusted for grain size, were consistently higher than those for YAG. The Nabarro–Herring mechanism best describes the creep of polycrystalline doped and undoped YAG in air and steam for all samples except those with a grain size less than 0.5 µm. The creep mechanism for polycrystalline LuAG was not determined and may be a complex combination of mechanisms. Creep mechanisms for polycrystalline garnets are compared and discussed.

One-step synthesis of high-entropy diboride (HEB) samples from oxide-based precursors is reported in this study. HEB samples (Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)B₂ are prepared from metal oxide starting powders using reactive spark plasma sintering (R-SPS) to conduct borocarbothermal reduction (BCTR) and sample densification in an individual high-temperature processing unit. Excess precursor C black is added to the HEB precursor powders to aid in reducing residual oxygen in the final samples. The effect of precursor C black concentration on the phase state and microstructure of HEB samples is characterized. This study demonstrates that the conversion from metal oxide powder to the HEB through BCTR depends on the precursor C black concentration, which influences the secondary phase formation and microstructural features. The results reveal that 3.9 wt.% C black provides the optimal balance of oxide-to-HEB conversion, a more homogeneous microstructure, and intermediate grain sizes than HEB samples with both lower and higher amounts of precursor C black (0, 1.8, and 7.5 wt.%). We demonstrate the production of HEB samples from inexpensive oxide-based precursor powders through BCTR and sample densification using an individual high-temperature processing unit via R-SPS.

Reactive direct current (DC) magnetron sputtering (rDCMS) and reactive high target utilization sputtering (rHiTUS) of compositionally complex TiZrHfVNbTa–N coatings were systematically investigated with varying nitrogen flow. The study combined experimental measurements of total and partial nitrogen pressures with simulations based on Berg's model. Both deposition systems exhibited hysteresis-free behavior, characterized by two distinct nitrogen consumption regimes: (1) a nearly linear increase up to a critical nitrogen flow (≈4 sccm in rDCMS and ≈6 sccm in rHiTUS), and (2) a saturation regime. Simulations reproduced these trends and confirmed that hysteresis suppression originates from high pumping speeds (pumping speed/volume ratio > > 4 s⁻¹). The applicability of Berg's model to rHiTUS was validated by the strong agreement between experiments and modeling, supporting the assumption that the fundamental processes of reactive sputtering—target sputtering, poisoning, and nitride formation—are identical in DCMS and HiTUS. The main technological benefit of operating in a hysteresis-free regime is that coating composition and properties can be controlled solely through nitrogen flow adjustment.