Electrical properties of ZnO varistors prepared by direct mixing of constituent phases

Abstract

Varistor samples containing different amounts of constituent phases were prepared by direct mixing of constituent phases. Detailed electrical characterization was performed to explain the influence of minor phases (spinel and intergranular phases) on overall properties. Characterization included investigation of the non-linear coefficients (alpha), breakdown electric field (E-B), leakage currents (J(L)), grain boundary barrier hight (Phi(B)) and constant beta from current-voltage characteristics, as well as calculation of activation energies for conduction (E-A) from ac impedance spectroscopy in the temperature interval 30-410 degrees C. Varistors sintered at 1100 degrees C for 1 h showed pronounced differences in electrical properties depending on relative molar ratios of the phases. Results were discussed in the sense of possible reduction of the content of minor phases in ZnO varistors.