Over the past twenty years, there has been high demand for novel functional materials for use in high-capacity dielectrics. Perovskite-type oxynitrides, which are derived from the introduction of nitrogen atoms into their corresponding oxides, possess a variety of improved chemical and physical properties. The dielectric performance of BaTa(O,N)₃ is highly dependent on its purity, density, and microstructure. However, conventional sintering methods often result in low-density samples (< 90% theoretical density) with many impurities, leading to poor dielectric properties. In this study, we adopted a two-step sintering method, i.e., rapid spark plasma sintering at a lower temperature followed by postannealing in flowing ammonia at a higher temperature, to obtain BaTa(O,N)₃ ceramic bulks with both high density and purity (up to 96.7% theoretical density and 97.94 wt% oxynitride phase content). The average particle size is 281.1 nm, with a uniform distribution of all the elements. The measured dielectric constant is as high as 2.1×10⁵ at 100 Hz (room temperature), which surpasses the values reported for other oxynitride dielectrics. A notable and unusual dielectric enhancement was observed at elevated temperatures, with the value reaching ~10⁷ at 200−250 °C. This mechanism can be attributed to defect-mediated polarization, including anion-ordering-induced permanent dipoles and oxygen vacancies, and thermally activated reconfigurable polar nanoregions that are verified by calculation and in situ transmission electron microscopy (TEM) analysis. These findings establish a general pathway to fabricate dense oxynitride ceramic bulks with high purity and collective permittivity for prospective applications in high-performance dielectric devices.

Silicon nitride foams with a hierarchical porous structure was formed by the combination of protein-based gelcasting, chemical vapor infiltration, and in-situ growth of silicon nitride nanowires. The porosity of the foams can be controlled at 76.3-83.8 vol% with an open porosity of 70.2-82.8 vol%. The pore size distribution was presented in three levels: < 2 μm (voids among grains and cross overlapping of silicon nitride nanowires (SNNWs)), 10-50 μm (cell windows), and >100 μm (cells). The resulted compressive strength of the porous bodies at room temperature can achieve up to 18.0±1.0 MPa (porosity = 76.3 vol%) while the corresponding retention rate at 800 ℃ was 58.3%. Gas permeability value was measured to be 5.16 (cm³·cm)/(cm²·s·kPa). The good strength, high permeability together with the pore structure in multiple scales enabled the foam materials for microparticle infiltration applications.