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.