In this study we aims to examine the effects of Co3O4 and NiO doping on the defects and electrical properties in ZnO-Bi2O3-Sb2O3 (Sb/Bi=0.5) varistors. It seemed to form □(0.20 eV) and □(0.33 eV) as dominant defects in Co and Ni co-doped ZBS system, however only □appeared in Co- or Ni-doped ZBS. Even though the same defects it was different in capacitance (1.5∼4.5 nF) and resistance (0.3∼9.5 kΩ). The varistor characteristics were improved with Co and Co+Ni doping (non-linear coefficient, α= 36 and 29, relatively) in ZBS. The various parameters (Nd= 1.43∼2.33×1017 cm-3, Nt=1.40∼ 2.28×1012 cm-2, Φb= 1.76∼2.37 V, W= 98∼118 nm) calculated from the C-V characteristics in our systems did not depend greatly on the type of dopant, which were in the range of a typical ZnO varistors. It should be derived a improved C-V equation carefully for more reliable parameters because the variation of the varistor capacitance as a function of the applied dc voltage is depend on the defect, frequency, and temperature.
