Influence of microstructure on the non-ohmic behavior of zinc oxide varistor ceramics prepared by direct mixing of constituent phases

Abstract

Well ground powders of zinc oxide sample were doped with mixtures of 2% MnO₂, 3% PbO and 3% MnO₂, 2% PbO. These were pressed and sintered at temperatures from 750⁰ C to 850⁰ C from different times from 12 to 42 hours, to diversify the microstructures of the resulting varistors. Grain sizes and distribution of phases were examined by the use of scanning electron microscope (SEM) and x-ray diffraction (XRD) techniques. Nonohmic
properties were obtained from the electrical field – current density characteristics. These were related to the microstructural properties. Experimental findings revealed that smaller grain sizes corresponded to higher non-linearity coefficients and breakdown fields. The barrier formation mechanisms were proposed as responsible for the microstructure-controlled non-ohmic behavior of the varistor samples.

Keywords: ZnO Ceramics, Varistor, Microstructure, Non-ohmic Properties, Electrical Characteristics