The effect of sintering temperature on the microstructure and the electrical response of liquid phase sintered ZnO-V2O5 varistor ceramics were analyzed using A.C impedance spectroscopy on samples prepared via conventional solid route. The impedance spectra were analyzed with the help of the model equivalent circuit at high frequencies and another at low frequencies, involving both resistor and constant phase element (CPE). The results indicate a significant contribution of grain boundary resistance to the non-ohmic characteristic of the studied materials.
The products were characterized regarding phase with X-ray diffraction, microstructures with SEM. Electrical characteristics were studied with impedance analysis and current-voltage characterization. In the present investigations studies, have been made on the effect of sintering temperatures (850°C, 900°C, and 950°C) on the microstructure and electrical properties of MnO and MgO doped ZnO-0.5 mol% V2O5 varistor system. The phase composition of samples consists mainly ZnO grains, while Zn2VO4 is the secondary phases. Better varistor performance has been achieved for the samples sintered at 950°C with nonlinear coefficient α=16, breakdown voltage 2513.3 V/mm and leakage current is JL=7.7 × 10-5 A/cm2. SEM analysis of morphology shows that the grain growth increases with increase in sintering temperature.
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