Voltage Enhancement of ZnO Oxide Varistors for Various Y2O3Doping Compositions

The microstructure and the electrical properties of a ZnO varistor, which was composed of a ZnO- $Bi_2O_3$ - $Sb_2O_3$ -CoO- $MnO_2$ -NiO- $Nd_2O_3$ system, were investigated at various $Y_2O_3$ addition concentrations. $Y_2O_3$ played a role in the inhibition of the grain growth. As the $Y_2O_3$ content increased, the average grain size decreased from $6.8{\mu}m$ to $4{\mu}m$ , and the varistor voltage( $V_{1mA}$ ) greatly increased from 275 to 400 V/mm. The nonlinearity coefficient ( $\alpha$ ) decreased from 72 to 65 with increasing $Y_2O_3$ amount. On the other hand, the leakage current ( $I_L$ ) increased from 0.2 to 0.9 ${\mu}A$ . These results confirmed that doping the varistors with $Y_2O_3$ is a promising production route for production of a higher fine-grained varistor voltage ( $V_{1mA}$ ) which can dramatically reduce the size of the varistors.