Relation between residual voltage ratio and microstructural parameters of ZnO varistors

The effect of thickness on residual voltage ratio K_r of ZnO varistors is experimentally studied, which shows that a dimensional effect of K_r also exists. The relations are experimentally investigated between residual voltage ratio K_r and breakdown strength E_1mA, and K_r and microstructural parameters. It is shown that K_r decreases with E_1mA, and increases with average grain size μ. An integrated parameter the product of average grain size μ and grain size variance σ² is found to be a better parameter to show the relation between electrical properties and microstructure of ZnO varistors. A microstructural model for simulation is proposed. By using computer, the relations are simulated between K_r and thickness, K_r and average grain size μ & K_r and the product σ²μ. The simulated results are consistent with experimental ones