Excellent DC aging behavior of ZnO–Pr 6O11–CoO–Cr2O3–Y2O3 ceramics modified with Tb4O7

The microstructure, electrical properties, and aging behavior of the ZnO–Pr 6O11–CoO–Cr2O3–Y2O3 varistor ceramics modified with Tb4O7 were investigated. The microstructure consisted of ZnO grain and an intergranular layer (Pr-, Y-, and Er-rich phases) as a secondary phase. The increase in the amount of Tb4O7 decreased the average grain size from 8.0 to 4.6 μm and increased the sintered density from 5.72 to 5.82 g/cm3. As the amount of Tb4O7 increased, the breakdown field increased significantly from 2886 to 6902 V/cm and the nonlinear coefficient increased from 32.5 to 40.3 at 0.75 mol%. The varistor ceramics added with 0.5 mol% Tb4O7 exhibited excellent stability by exhibiting −0.1% in the variation rate of the breakdown field and −0.3% in the variation rate of the nonlinear coefficient for aging stress state of 0.95 E1 mA/150 °C/24 h.