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 dimensional effect of K-r also exists. The relations are experimentally investigated between residual voltage ratio K-r and breakdown strength E-1mA, & K-r and microstructural parameters. It is obtained that K-r decreases with E-1mA, increases with average grain size mu. An integrated parameter-the product of average grain size mu and grain size variance sigma(2) 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 mu & K-r and the product sigma(2)mu. The simulated results are consistent with experimental ones.