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

The past twenty years have witnessed the high demands for novel functional material family to be used in high-capacity dielectrics. Perovskite-type oxynitrides which are derived from the introduction of nitrogen atoms into their corresponding oxides, possess a diversity 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 lots of impurities, leading to poor dielectric property. In this study, we adopted a two-step sintering method, i.e., rapid spark plasma sintering at a lower temperature followed by post annealing 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 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 level at 200−250 ℃. The mechanism can be attributed to defect-mediated polarization, including anion-ordering-induced permanent dipoles and oxygen vacancies, and thermally activated reconfigurable polar nanoregions that is verified by calculation and in situ TEM analysis. These findings establish a general pathway to fabricate dense oxynitride ceramic bulks with high purity and colossal permittivity for the prospective applications on high-performance dielectric devices.