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 0.95V 1mA/150 deg. C/24 h