Nonlinearity Characteristics of Low-Voltage Barium Titanate Based Zinc Oxide Varistor Ceramics Modified by Cobalt Dopants

Abstract

Application of ZnO varistor at low voltage has increased significantly due to the high demands of low-voltage electronics with high nonlinearity characteristics and low leakage current. The varistor ceramics were developed via solid-state reaction method and the resultant sample was analyzed by means of SEM, EDS and XRD. The nonlinearity characteristics of ZnO varistor ceramics for different contents of cobalt oxide (Co₃O₄) at a given barium titanate (BaTiO₃) amount were analyzed based on the J-E characteristics measurement. The increased value of nonlinear coefficient (α) equal to 4.8 was exhibited by the sample made with 12 wt.% BaTiO₃ additive. As the concentration of dopant (Co₃O₄) incorporated was increased from 0.5 to 1.5 wt.%, the varistor voltage limit decreased from 8.9 V/mm to 7.0 V/mm, respectively. Additionally, the barrier height increased from 0.88 to 0.98 eV for 0.0 wt.% to 1.0 wt.% of Co₃O₄ concentration, respectively. The highest α of 7.2 was obtained at 0.5 wt.% Co₃O₄ and decreased with further doping content due to to the reduction of barrier height caused by the variation of electronic state at the grain boundaries.