Correlation between Dielectric Constant Change and Oxidation Behavior of Silicon Nitride Ceramics at Elevating Temperature up to 1,000 °C

Abstract

In this study, the high-temperature dielectric constant of Si<sub>3</sub>N<sub>4</sub> ceramics, a representative non-oxide-based radome material, was evaluated and the cause of the dielectric constant change was analyzed in relation to the oxidation behavior. The dielectric constant of Si<sub>3</sub>N<sub>4</sub> ceramics was 7.79 at room temperature, and it linearly increased as the temperature increased, showing 8.42 at 1,000 °C. As results of analyzing the microstructure and phase for the Si<sub>3</sub>N<sub>4</sub> ceramics before and after heat-treatment, it was confirmed that oxidation did not occur at all or occurred only on the surface at a very insignificant level below 1,000 °C. Based on this, it is concluded that the increase in the dielectric constant according to the temperature increase of Si<sub>3</sub>N<sub>4</sub> ceramics is irrelevant to the oxidation behavior and is only due to the activation of charge polarization.