Grainboundary electronic structure of ZnO-Bi₂O₃ based varistor ceramics

Dielectric frequency spectra of ZnO-Bi₂O₃ based varistor ceramics were measured in the frequency range of 10^-2Hz-10⁶Hz from -100°C to 20°C by Novocontrol broadband dielectric spectrometer. The intrinsic defect structure of ZnO was calculated according to the theory which assumes that characteristics dielectric loss peaks of ZnO varistor ceramics origin from electronic relaxation process of intrinsic defects in depletion layer. At the same time the micro-electric parameters of grainboundary and the single grainboundary breakdown voltage V_b were obtained. The accordance of theory with experiment in V_b value indicates that the method to calculate grainboundary electronic structure by dielectric spectroscopy proposed in this paper is reasonable.