Electrical properties of ZnO varistor ceramics modified by rare earth-yttrium and gallium dopants

Scanning electron microscopy, electric field-current density measurements, capacitance-voltage testing, X-ray diffraction analysis, and energy dispersive X-ray spectroscopy were performed to study the effects of rare earth-yttrium and gallium doping on the microstructure and electrical properties of ZnO varistors. Our results indicated that the introduction of gallium and yttrium strengthened the barrier height of grain boundaries and led to a decrease in the grain resistance. Both the voltage gradient and nonlinear coefficient of the samples increased and then decreased as the gallium doping level was increased at a given rare earth-yttrium. The residual voltage ratio and the leakage current varied with the opposite relationship. The findings of this study could help to improve the protective effects of surge protection devices assembled from ZnO ceramic varistors and enhance the stability of power systems. (C) 2018 Elsevier B.V. All rights reserved.