Effect of co-doping Y2O3–La2O3 on microstructure and electrical properties of ZnO-based varistor ceramics prepared from nanosize ZnO powder

ZnO-based varistor ceramics doped with fixed La2O3 and different Y2O3 have been fabricated by the conventional solid-state reaction route. Phase composition, microstructure, and electrical properties were studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and direct current electrical measurement. The Y2O3 phase, Y-rich phase and La-rich phase were found to distribute along the grain boundaries of predominant ZnO grains from XRD and SEM analyses. The average grain size of the primary phases was calculated to be in the range of 3.80 to 4.17 μm. The varistor ceramic doped with 0.1 mol% La2O3 and 0.5 mol% Y2O3 sintered at 1100 °C for 2 h exhibited high comprehensive electrical properties with the breakdown field of 1055 V/mm, the nonlinear coefficient of 65.5 and the leakage current of 0.6 μA. The results illustrated that co-doping La2O3 and Y2O3 and employing the ZnO powder in nanometer size may be a promising route to obtain varistor ceramics with excellent electrical properties.