Relaxation peaks of ZnO varistors and their correlations with electrical properties

Abstract

Many dielectrics exhibit a (polarization) relaxation response when a time-varying electric field is applied. In some frequency bands, the amplitude of the polarization changes rapidly, with a significant dielectric loss; the maxima in the change rate are referred to as relaxation peaks. ZnO varistors exhibit a dielectric response with several relaxation peaks, but the relationship between the relaxation peaks and electrical properties has not been established. To understand this relationship, dielectric spectroscopy measurements of ZnO varistors were conducted in the temperature range of −110 °C to 200 °C in the frequency range of 10−1–106 Hz. By changing two important dopants of Bi2O3 and Sb2O3, four relaxation peaks, named Peak A, Peak B, Peak C, and Peak D, were detected. It was found that peaks A, B, and D are indispensable for higher nonlinearity and lower leakage current density. The detection of all four peaks implies that ZnO varistors possess excellent electrical properties, that is, a high breakdown field (235.2 V mm−1), nonlinear coefficient (76.2), and low leakage current density (0.065 μA cm−2).