Influence of spinel phase composition on ZnO varistors properties

The method of directed synthesis of the constituent phases (DSCP) was applied to investigate the influence of spinel phase composition on characteristics of ZnO varistors. Six varistor mixtures differing only in chemical composition of the spinel phase were prepared. The phase ratio as well as the compositions of ZnO and intergranular gamma-Bi2O3 phases were the same in all samples. Characterization of prepared varistors was performed by X-ray diffraction, SEM and electrical measurements. It was shown that it is possible, in certain cases, to estimate additive redistribution taking into account changes in lattice constants of ZnO, spinel phases and varistor composition. Comparison of six different raristor mixtures shows that it is possible to reduce the number of components of the system if all main constituents of the varistor microstructure are still present. Results confirmed advantages of the DSCP method in preparation of varistors of required phase composition and properties.