Rapidly synthesized dense BaTa(O,N)₃ ceramics with high permittivity

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.