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

The V 2 O 5 -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 V 2 O 5 -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/cm 2 . The corresponding intrinsic parameters are φ b =0.63 eV and N d =2.37×10 24 m -3 .