Electrical properties of ZnO varistors prepared by microwave and conventional sintering process

Abstract

The Bi2O3-based ZnO varistor materials were prepared by 2.45 GHz microwave, 24 GHz millimeter-wave or conventional-sintering processes. Both millimeter-wave and microwave sintering processes are superior to the conventional sintering process in densifying the Bi2O3-based ZnO materials. Large nonlinear coefficient and low leakage current density were attained by sintering the samples under the 1200°C sintering temperature and 5 min soaking time, A high density as 96.7% T.D. (theoretical density) has been achieved. However, the varistor characteristics, including breakdown voltage (Vbk), nonlinear coefficient (α) and leakage current density (JL), degraded markedly for the samples sintered at too long soaking time (10 min), which was ascribed to the occurrence of abnormal grain growth, in accompany with the loss of Bi2O3 and ZnO species.