Influence of CoO on stability of nonlinear electrical properties and dielectric characteristics in Pr6O11-based ZnO varistor ceramics

The nonlinear electrical properties, dielectric characteristics, and stability of the varistor ceramics of Zn–Pr–Co–Cr–Dy oxide system were investigated at various CoO contents. The sintered density of varistor ceramics increased from 5.25 to 5.55 g cm−3 with increasing CoO contents. The varistor voltage decreased from 235.3 to 86.0 V mm−1 with increasing CoO contents. As the CoO content increased, the nonlinear exponent increased up to 1.0 mol.% CoO, whereas further incorporation decreased the nonlinear exponent. Varistor ceramics containing 1.0 mol.% CoO exhibited the highest nonlinearity, in which the nonlinear exponent was 66.6 and the leakage current was 1.2 μA. Furthermore, varistor ceramics containing 1.0 mol.% CoO exhibited the highest stability, where the variation rate of varistor voltage, nonlinear exponent, and leakage current were −1.9%, −10.9%, and +275%, respectively, under DC accelerated aging stress of 0.95V1 mA/150 °C/24 h.