Abstract
The electrical properties and stability of ZPCE varistors consisted of $ZnO-Pr_6O_{11}-CoO-Er_2O_3$ ceramics were investigated. $ZnO-Pr_6O_{11}-CoO-Er_2O_3$ based ceramics were sintered at $1300^{\circ}C$ and $1350^{\circ}C$, respectively, without and with 0.5 mol% $Er_2O_3$. The varistors sintered at $1300^{\circ}C$ exhibited a better nonlinearity than that $1350^{\circ}C$. The varistors with $Er_2O_3$ of 0.5 mol% exhibited a high nonlinear exponent of 52.8. However, they easily degraded due to the low density below 85% of TD. On the other hand, the varistors sintered at $1350^{\circ}C$ without $Er_2O_3$ exhibited an extremely poor nonlinearity, but the varistors with $Er_2O_3$ of 0.5 mol% exhibited a relatively good nonlinearity, which the nonlinear exponent is 34.8 and the leakage current is $7.4\;{\mu}A$ Morever, they exhibited a very high stability, which the variation rate of varistor voltage, nonlinear exponent, and leakage current are -0.9%, -2.9%, and +2.7%, respectively, under the third stress $(0.80 V_{1mA}/90^{\circ}C/12h)$ + $(0.85 V_{1mA}/115^{\circ}C/12h)$ + $(0.90 V_{1mA}/120^{\circ}C/12h)$. Consequently, it was estimated that $ZnO-Pr_6O_{11}-CoO-Er_2O_3$ ceramics will be usefully applied to develop the advanced $Pr_6O_{11}$-based ZnO varistors.