Abstract

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Zinc oxide ceramic varistors were realized by doping ZnO with small quantities of MnO2 and PbO. The preparation technique of Direct Mixing of Constituent Phases (DMCP) was used. The samples were pelletized at a pressure of 1.24 X 103 N/cm2 and sintered in ambient atmosphere at a temperature of 850°C for a period of 36hours. They were characterized by measuring the current-voltage response to evaluate the non-ohmic behaviour. Breakdown threshold voltages of 2.02 X 103 V/m and 4.80 X 103 V/cm were recorded at currents 1.05 A/cm2 and 1.20A/cm2 respectively. Microstructural analyses were carried out using x-ray diffraction and scanning electron microscopy techniques. The XRD spectra re vealed the formation of structures and polymorphs of the additives in the sample while the SEM mi crographs revealed the sizes, types and distribution of grains in the matrix. The grain sizes for the re spective sample types were obtained as 1.621 µm and 1.020 µm. The microstructural analysis gave good correlation with the electrical response of the varistor samples.

Keywords: Ceramic varistors, electrical characteristics, threshold voltage, SEM micrographs, x-ray diffraction spectra.