Effect of Er2O3 addition on the microstructure, electrical properties, and stability of Pr6O11-based ZnO ceramic varistors

The microstructure, electrical properties, and stability of Pr6O11-based ZnO varistors, which are composed of ZnO-Pr6O11-CoO-Er2O3 systems, were investigated with Er2O3 additive content. The density of ceramics was in the range of 84-88% of TD at 1300 C and 93-98% of TD at 1350°C, and greatly affected the stability. Most of the added-Er2O3 were segregated at nodal points. The varistors with 0.5 mol% Er2O3 sintered at 1300 °C exhibited the best nonlinear current-voltage characteristics, which the nonlinear exponent is 52.8 and the leakage current is 9.8 μA. All the varistors sintered at 1300 °C, even under relatively weak stress, exhibited the thermal runaway within short time in order of high leakage current. On the contrary, the stability of varistors sintered at 1350 °C exhibited far higher stability than that at 1300 °C. Particularly, the varistors with 0.5 mol% Er2O3 exhibited not only relatively good nonlinear current-voltage characteristics, which the nonlinear exponent is 34.8 and the leakage current is 7.4 μA, but also excellent stability, which the variation rates of varistor voltage, nonlinear exponent, and leakage current are below 1%, 3%, and 3%, respectively, even under more severe stress such as (0.80 V1 mA/90 °C/12 h) + (0.85 V1 mA/ 115 °C/12 h) + (0.90 V1mA/120°C/12 h).