Microstructure, electrical properties, and aging behavior of ZnO–Pr6O11–CoO–Cr2O3–Y2O3–Er2O3 varistor ceramics

The microstructure, electrical properties, and aging behavior of the ZnO–Pr6O11–CoO–Cr2O3–Y2O3–Er2O3 varistor ceramics were investigated for different contents of Er2O3. The microstructure consisted of ZnO grain and an intergranular layer (Pr, Y, and Er-rich phases) as a secondary phase. The increase of Er2O3 content decreased the average grain size and increased the sintered density. As the Er2O3 content increased, the breakdown field increased from 4206 V/cm to 5857 V/cm and the nonlinear coefficient increased from 32.6 to 48.6. The varistor ceramics added with 1.0 mol% Er2O3 exhibited excellent stability by exhibiting −0.2% in the variation rate of the breakdown field and −2.7% in the variation rate of the nonlinear coefficient for aging stress of 0.95 E1 mA/150 °C/24 h.