Electrical properties and stability against DC accelerated aging stress of lanthania doped praseodymia-based zinc oxide varistor ceramics

The microstructure, electrical properties, and stability against DC accelerated aging stress of the varistor ceramics, which are composed of ZnO–Pr₆O₁₁–CoO–Cr₂O₃–La₂O₃-based ceramics, were investigated for various La₂O₃ contents. The increase of La₂O₃ content led to more densified ceramics, whereas abruptly decreased the nonlinear properties by incorporating beyond 1.0 mol%. The highest nonlinearity was obtained from 0.5 mol% La₂O₃, in which the nonlinear exponent is 81.6 and the leakage current is 0.1 μA. As the La₂O₃ content increased, the donor concentration increased in from 0.64 × 10¹⁸ to 16.89 × 10¹⁸/cm³ and the barrier height greatly decreased with increasing La₂O₃ content, reaching a maximum (1.47 eV) in 0.5 mol% La₂O₃. The varistors doped with 0.5 mol% La₂O₃ exhibited high stability, in which the variation rates of varistor voltage, nonlinear exponent, and leakage current were −1.14%, −3.7%, and +100%, respectively, for stressing state of 0.95 V _1 mA/150 °C/24 h.