Microstructure and Electrical Properties of ZPCCYT Varistor Ceramics

The Microstructure and nonlinear electrical properties of the ZPCCYT (ZnO- $Pr_6O_{11}$ -CoO- $Cr_2O_3$ - $Y_2O_3$ - $Tb_4O_7$ ) varistors were investigated for different amounts of $Tb_4O_7$ . The addition of $Tb_4O_7$ has a significant effect on microstructure and electrical properties. Analysis of the microstructure indicated that the ceramics consisted of ZnO grain as a main phase and a few secondary phases as a mix of $Pr_6O_{11}$ , $Y_2O_3$ , and $Tb_4O_7$ . As the amount of $Tb_4O_7$ increased, the sintered densities of pellets increased from $\rho$ = 5.70 to $5.78g/cm^3$ and the average grain size decreased from d = 4.8 to $3.6{\mu}m$ . The increase in the amount of $Tb_4O_7$ increased from $E_B$ = 7,473 to 10,035 V/cm and from ${\alpha}$ = 39.7 to 52.2. In particular, it was found that the ceramics modified with 1.0 mol% in the amount of $Tb_4O_7$ are suited for the varistors for high voltage in the light of a high sintered density and a high voltage gradient.