Surface layer and its effect on dielectric properties of SiC ceramics

The dielectric properties of SiC ceramics were investigated in the temperature range from room temperature to 873 K and frequency range from 102 to 106 Hz. Giant dielectric behavior was observed in SiC ceramics in the temperature range above 600 K. This behavior strongly depends on sample thickness. Our results revealed that the surface of the sintered SiC sample was covered by a SiO2 layer. Oxygen vacancies in the surface layer diffuse into the inner part giving rise to two thermally activated dielectric relaxations. The low-temperature relaxation was argued to be a polaron relaxation caused by the hopping motions of oxygen vacancies, whereas the high-temperature one is a Maxwell-Wagner relaxation mainly caused by the surface layer.