Ultra-high breakdown field varistors prepared from individually synthesized nanoprecursors

Previously synthesized nanocrystalline ZnO doped with cobalt and manganese, Bi2O3 and Sb2O3 were the precursors for high voltage varistors preparation. Varistor ceramics were sintered at 750 °C, 770 °C or 900 °C for 1 h. An amount of 30 mass% of secondary phases and sintering temperature of 770 °C were found to be optimal for obtaining varistor with prominent properties. Achieved density was 97% of the theoretical value. Post-sintering phase composition included ZnO, γ-Bi2O3 and pyrochlore-type with Zn2Bi3Sb3O14 nominal formula. Fine grained microstructure was accompanied with good phase distribution and excellent electrical characteristics: extraordinary high breakdown field of 3200 V mm−1, high nonlinearity coefficients of 71 and 51 in 0.1-1 and 1-10 mA cm−2 current density ranges, respectively, and low leakage current of 7.7 μA cm−2.