Low-residual-voltage ZnO varistor ceramics improved by multiple doping with gallium and indium

In this work, we studied multiple doping of ZnO varistors with Ga2O3 and In2O3 and determined its effect on electrical properties, characterized by using scanning electron microscopy, current-voltage testing, capacitance-voltage testing, and X-ray diffraction. At a given gallium concentration, the residual voltage ratio of the sintered varistors decreased clearly with the indium dopant concentration increased. Additionally, with increasing indium dopant concentration, the average grain size decreased slightly, and the voltage gradient was improved. The varistors containing 0.045 mol% indium and 0.4 mol% gallium showed optimal performance, exhibiting a residual voltage ratio of 1.54, as well as a voltage gradient of 462.5 V/mm, a leakage current of 1.30 µA/cm2, and nonlinear coefficient of 72.3. Such co-doped ZnO varistors can provide better protection when used in surge protectors.