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

In this study, the high-temperature dielectric constant of Si3N4 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 Si3N4 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 Si3N4 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 Si3N4 ceramics is irrelevant to the oxidation behavior and is only due to the activation of charge polarization.