Effects of aluminum doping on the microstructure and electrical properties of ZnO-Pr6O11-Co3O4-MnCO3-Y2O3 varistor ceramics

The effect of Al2O3 doping on the microstructure and electrical properties of the ZnO-Pr6O11-Co3O4-MnCO3-Y2O3 system was investigated in the range of 0.0–0.1mol%. The results reveal that Al2O3 doping has slight influence on the densification process. The microstructure of the ceramics comprises of ZnO phase, ZnAl2O4 spine phase and Pr-rich phases. The addition of Al2O3 greatly affects the electrical properties. The varistor voltage (E1mA/cm2) of ZPCMYAl samples decreases over a wide range from 5 530 V/cm to 1 844 V/cm with the increasing Al2O3 content. The nonlinear exponent(α) increases with the increasing Al2O3 content to 0.01mol%, whereas it is decreased by the further doping. The ZPCMYAl-based varistor ceramics with 0.01mol% Al2O3 exhibit the best electrical properties, with the nonlinear exponent (α) attaining the highest value of 33.4 and the lowest leakage current of 2.7 μA. The capacitance-voltage (C-V) measurement shows that the donor density (Nd) at the grain boundaries increase from 1.58×1018 to 3.15×1018 cm−3, the barrier height (φb) increases from 1.60 to 2.36 eV, and the depletion layer width (t) decreases from 24.9 to 21.6 nm.