Journal of the American Ceramic Society最新文献

Boron nitride (BN) powders with near-spherical particles of more than 10 µm were synthesized by templated carbothermal reduction and nitridation. The effects of processing factors, such as raw material mixing methods, C/B₂O₃ molar ratios, and carbon templates, were systematically studied, and the reaction mechanism was discussed. The experimental results showed that the integrity and morphology of the carbon templates was usually destroyed during ball milling or grinding, but preserved during magnetic stirring. The morphology of synthesized BN particles depended on the C/B₂O₃ molar ratio in starting reactant mixtures and gradually changed from sheet-like to near-spherical shape with decreasing C/B₂O₃ molar ratio. The morphology and size of synthesized BN particles agreed with that of the carbon templates, which means that the morphology and size of synthesized BN particles can be tailored by controlling that of the carbon template. The BN near-spherical particles synthesized in this work may be used as thermally conductive fillers for electronic packaging.

Gallium oxide (Ga₂O₃) has attracted much attention due to its promising applications in optical and electronic devices, while it is difficult to fabricate high-quality Ga₂O₃ transparent ceramics because of the non-cubic crystal structure. In this work, fully densified undoped and rare earth (RE = Tb, Dy. Er)-doped Ga₂O₃ transparent ceramics were successfully fabricated by using spark plasma sintering (SPS) and co-precipitated ceramic powders. Both the powders and ceramics showed pure monoclinic β- Ga₂O₃ crystal structure and unique orientation. After sintering by SPS for 30 min, all the ceramics reached a relative density higher than 99.21%. The total transmittance of RE-doped Ga₂O₃ transparent ceramics ranges from 60% to 69% originating from the oriented and dense microstructures. The photoluminescence spectra and fluorescence lifetime of RE-doped Ga₂O₃ transparent ceramics confirm characteristics of energy transfers corresponding to Tb³⁺, Dy³⁺, or Er³⁺ ions in the visible and NIR spectral region. This study demonstrates that oriented RE-doped Ga₂O₃ transparent ceramics have great potential to be used in various optical applications.

Calcium zirconate (CaZrO₃)-based fibrous membrane is a promising candidate in high-temperature areas for its high melting point, good phase stability up to 1900°C, low thermal conductivity, and low cost. To further enhance the high temperature flexibility of CaZrO₃-based fibrous membrane without sacrificing stability, modification methods should be conducted. In the present work, a CaZrO₃-BaZrO₃ dual-phasic structure was proposed to modify the high-temperature properties from the standpoint of phase competition. CaZrO₃-BaZrO₃ fibrous membranes were prepared with the combination of the electrospinning method and pyrolysis process. The decomposition process, phase transformation, crystallize size, and microstructure evolution of CaZrO₃-BaZrO₃ precursor fibrous membrane were characterized. The grain size, particle size, NIR reflectivity, high-temperature stability, fire retardancy, and high-temperature flexibility were also characterized and compared with other CaZrO₃-based fibrous membranes. The higher thermal stability and flexibility of the CaZrO₃-BaZrO₃ fibrous membrane at 1200°C would make it a good candidate for high-temperature insulating, high-temperature supporting, and high-temperature filtration.

Topological constraint theory (TCT) and molecular dynamics simulations (MD) are utilized to study the effect of Y₂O₃/SiO₂ substitution on the short- and medium-range structures and properties in aluminosilicate glasses containing Y₂O₃. Experimental methods have been applied to characterize the structures of the as-prepared glasses to verify the accuracy of MD simulations. It was found that the Y–O bond distance is around 2.38 Å and the Y average coordination number is around 5.78. The introduction of Y₂O₃ disrupts the Si–O and Al–O bonds in the network structure and elevates the proportion of non-bridging oxygen. Meanwhile, the calculation results of Si–O and Al–O bond distances show Y shortens the distance between Si, Al cations and oxygen ions, improving the network structure tightness. Furthermore, the glass transition temperature (T_g), Vickers hardness (H_V), and elastic modulus (E) of glass increase with the increase of Y₂O₃ content, while the viscosity decreases. TCT was used to analyze the relationship among glass compositions, structures, and properties, and the properties prediction models for T_g, H_V, and E were established. The effectiveness of TCT prediction models was proved by the comparison between the results predicted by the models and the data reported in the literature.

This study presents the successful synthesis of Sr₂Ta₂O₇ with a pyrochlore crystal structure, which was previously unreported. Traditionally, Sr₂Ta₂O₇ is synthesized in an orthorhombic layered perovskite-type structure using traditional solid-state reaction and batch-type subcritical hydrothermal methods. Here, we utilize a continuous-flow supercritical hydrothermal method, a technique primarily applied for nanoparticle synthesis and minimally explored for the synthesis of metastable crystals. Through detailed evaluations employing X-ray diffraction and scanning electron microscopy, we confirmed the synthesis of the pyrochlore phase, characterized by particles with a diameter of less than 100 nm, synthesized at 633 K. Notably, the synthesized pyrochlore structure demonstrated remarkable stability, even after thermal treatment at 773 K for 1 h. Pyrochlore Sr₂Ta₂O₇ stands out as a rare exception to the traditional tolerance factor approach among 278 known A₂B₂O₇ compositions. Systematic evaluation of formation energies through first-principles calculations revealed that the pyrochlore Sr₂Ta₂O₇ synthesized in this study is located 0.06 eV/atom above the convex hull. This achievement underscores the potential of the continuous-flow supercritical hydrothermal method in automating the exploration and discovery of novel crystal structures, suggesting a systematic pathway for advancing the field of material synthesis.

Phosphate invert glasses (PIGs) exhibit excellent biocompatibility because of their high chemical durability and controlled ion releasability. PIGs are composed of short phosphate units such as ortho- and pyrophosphate. This structure makes it difficult to obtain clear glass using the melt-quenching method. Our previous work reported that intermediate oxides (such as TiO₂ and Nb₂O₅)-containing PIGs exhibit good glass-forming ability and ion dissolution controllability. This work used a liquid-phase method to prepare PIGs at room temperature and pressure. Furthermore, TiO₂ was used to control ion releasability for biomedical applications. Titanium-containing PIGs were successfully prepared using a liquid-phase method. Pyrophosphate and titania formed P-O-Ti bonds with an increasing TiO₂ content in the glass, forming chain-like structural units such as (-O-P-O-P-O-Ti-O-)_n. The number of chain-like structures increased with an increasing TiO₂ content in the glass, improving the chemical durability. Hence, the ion releasability of titanium-containing PIGs prepared using the liquid-phase method can be controlled by the glass structure. Additionally, the PIGs exhibited good cell viability. Therefore, the PIGs are candidates for carriers of therapeutic inorganic ions for biomedical applications.

In recent years, transparent terbium gallium garnet (TGG) ceramics have garnered significant interest for their application in high-power Faraday isolators. However, challenges in achieving high transparency have led researchers to explore the addition of various sintering aids as a key strategy to enhance the optical quality of TGG ceramics. Through this work, the effect of germanium (Ge) addition on the microstructure and optical transparency of TGG magneto-optical ceramics was investigated. TGG powders were synthesized by the co-precipitation method, and the source Ge was Ge ethoxide added through a ball-milling step. Transparent TGG ceramics were prepared by air pre-sintering combined with hot isostatic pressing post-treatment and subsequent annealing. The ceramics containing 200 ppm Ge exhibit optimal transmittance of 81.3% at 1064 nm (a value of theoretical transmittance), the Verdet constant was −133.0 rad·T⁻¹·m⁻¹ at 633 nm. When the addition of Ge reaches 600 ppm, a secondary phase can be observed on the surface of ceramic. Subsequently, TGG ceramics prepared from 1425°C to 1500°C with 200 ppm of Ge were analyzed, which revealed that the optimal pre-sintering temperature is 1450°C.

This study investigated the synthesis mechanism of tantalum boride (TaB₂) powder via the boron/carbothermal reduction method, based on thermodynamic calculations and experimental results. The insufficient presence of the intermediate product B₂O₃ leads to the emergence of TaC and Ta₃B₄, while in the presence of a sufficient boron source in the reaction system, the primary products formed include TaB₂, TaC, and B₂O₃, with TaC subsequently reacting with B₂O₃ and carbon to yield TaB₂. TaB₂ powder was successfully synthesized at 1500°C with the addition of an excess of 20 wt% B₄C. The particle size of the powder was approximately 298 nm, and the oxygen content and carbon content in the powder were 0.6 and 0.1 wt.%, respectively.

Ionizing events having a wide variety of radiation-induced effects can radically affect the kinetics of defect production or structural transformation in the pyrochlore structured oxides (A₂B₂O₇). Therefore, a thorough understanding of the kinetics associated with cation ordering and disordering is required for various technological applications. The structural responses of Gd₂Ti_2-yZr_yO₇ (y = 0.4, 1.2, 1.6) pyrochlore series irradiated by 120 MeV Au⁹⁺ ions were investigated using in situ synchrotron x-ray diffraction (SR-XRD), micro-Raman spectroscopy, and scanning electron microscopy (SEM). Each pyrochlore composition irradiated at the highest fluence, where structural modifications occur, was subsequently isochronally annealed from room temperature to 1000°C. The SR-XRD results indicate that Ti-rich composition (y = 0.4) retains its pre-irradiated pyrochlore structure (Fd$�\overline{3}$m) at 1000°C. In contrast, Zr-rich compositions exhibit recrystallization to an intermediate defect-fluorite phase (Fm$�\overline{3}$m) above 500°C, and the pre-irradiated pyrochlore superstructure does not recover even on annealing at 1000°C. These results reveal that recrystallization temperature strongly depends on the accumulated radiation damage, generally described with the cationic radius ratio (r_A/r_B). Thus, investigation of the thermal annealing behavior of irradiated pyrochlores helps better understanding the general mechanisms of radiation damage and recovery of pyrochlores, which is important for their use in nuclear applications.