The relation between residual voltage ratio and microstructural parameters of ZnO varistors

The effect of the sample thickness d on the residual voltage ratio Kr indicates the existence of the dimensional effect in the commercial ZnO varistors. The empirical relations derived are based on experimental findings for Kr and breakdown electric field strength E1 mA cm−2 and the microstructural parameter average grain size μ. It is observed that Kr decreases with increasing E1 mA cm−2, while it increases with increasing μ. An integrated hybrid parameter σ2μ, obtained as the product of average grain size μ and grain size variance σ2, is found to be a representative relation between electrical properties and microstructure of the ZnO varistors. A microstructural model is used for computer simulation that also verified the dimensional effect in these varistors. The simulated results are consistent with the experimental results.