Influence of SiO2 on electrical properties of the highly nonlinear ZnO-Bi2O3-MnO2 varistors

The ZnO-Bi2O3-MnO2-xSiO2 (ZBMS) varistor was prepared at a low sintering temperature of 880 °C via the conventional solid state method. The phase transformation, microstructure, and electrical properties of the ZBMS varistor were studied as a function of doping amount of SiO2. It is showed that the growth of ZnO grain is restrained by the introducing of SiO2; and the grain size decreases from 4.68 μm to 2.98 μm. The breakdown voltage E1mA exhibits a simultaneous variation from 608.11 V/mm to 1232.88 V/mm. It is also revealed that SiO2 has a significant effect on the Schottky barrier structure. As a result, the highest barrier height φb of 5.34 eV is attained at a composition of x = 2.0 wt%, which contributes to the highest nonlinear coefficient α of 73.68. Moreover, all the samples show low leakage current of IL < 0.1 μA.