Degradation of ZnO varistor and its dielectric relaxation

Abstract

Dielectric relaxation spectra are used to study the degradation of a ZnO varistor under 8/20/spl mu/s impulse current. The relationship between dielectric relaxation spectra and the distribution of migration ions is investigated. Dielectric-relaxation measurement is shown to be a reliable method for studying the degradation of non-Ohmic ZnO ceramics. The frequency spectra of dielectric loss are shifted to low-frequency regions after stressing by impulse current. The shift is attributed to the formation of equivalent dipoles in the grain boundary by the migration of interstitials.<>