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

The effect of the sample thickness d on the residual voltage ratio K, indicates the existence of the dimensional effect in the commercial ZnO varistors. The empirical relations derived are based on experimental findings for K-r and breakdown electric field strength E1 mA cm-2 and the microstructural parameter average grain size mu. It is observed that K-r decreases with increasing E1 mA cm-2, while it increases with increasing mu. An integrated hybrid parameter sigma(2)mu, obtained as the product of average grain size mu and grain size variance sigma(2), 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. (C) 2004 Elsevier B.V. All rights reserved.