Microstructures and electrical properties of V2O5-based multicomponent ZnO varistors prepared by microwave sintering process

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 degrees C (10 min) but the grain growth was initiated only when sintered at a higher temperature than 1000 degrees C (10 min). The varistor characteristics, including breakdown voltage (V-bk), nonlinear coefficient (alpha) and leakage current density (J(L)), degraded markedly for the samples sintered at too high temperature (i.e., T greater than or equal to 1000 degrees C) and for too long period (i.e., t greater than or equal to 10 min) that was ascribed to the occurrence of abnormal grain growth. Contrarily, the intrinsic characteristics, including potential barrier height (phi(b)) and donor density (N-d), varied only moderately with these sintering conditions. The V2O5-based ZnO materials sintered at 1000 degrees C (5 min) possessed good varistor characteristics as V-bk = 248 V/mm, alpha = 31 and J(L) = 4.6 x 10(-5) A/cm(2). The corresponding intrinsic parameters are phi(b) = 0.63 eV and N-d = 2.37 x 10(24) m(-3).