Microstructures and Electrical Properties of V2O5-based Multicomponent ZnO Varistors Prepared by Microwave Sintering Process

Abstract

The V2O5-based ZnO varistor materials were successfully densified using microwave sintering process. The materials can reach a high density as 94.6% T.D. (theoretical density) when sintered at 800 °C (10 min) but the grain growth was initiated only when sintered at a higher temperature than 1000 °C (10 min). The varistor characteristics, including breakdown voltage (V bk), nonlinear coefficient (α) and leakage current density (J L), degraded markedly for the samples sintered at too high temperature (i.e., T≥1000 °C) and for too long period (i.e., t≥10 min) that was ascribed to the occurrence of abnormal grain growth. Contrarily, the intrinsic characteristics, including potential barrier height (φ b) and donor density (N d), varied only moderately with these sintering conditions. The V2O5-based ZnO materials sintered at 1000 °C (5 min) possessed good varistor characteristics as V bk=248 V/mm, α=31 and J L=4.6×10-5 A/cm2. The corresponding intrinsic parameters are φ b=0.63 eV and N d=2.37×1024 m-3.