Microstructure and current–voltage characteristics of ZnO–V 2O 5–MnO 2 varistor system

Abstract

The effects of sintering temperature and time on the microstructure and the electrical properties have been studied in a ZnO–0.5 mol%V 2O 5–2 mol%MnO 2 system. The microstructure of the samples consists mainly of ZnO grains with Zn 3(VO 4) 2 as the minority secondary phase. This minor secondary phase disappears for samples sintered at 1200 °C and above. An increase in sintering temperature also brings about a deleterious effect on the non-linear coefficient and the breakdown electric field. An optimum sintering time of 4 h at 900 °C gives the best electrical properties, with the non-linear coefficient α attaining a highest value of 31.8. Grain growth process is also investigated in terms of the phenomenological kinetic grain growth expression: G n=K o t exp(− Q RT ) . The kinetic grain growth exponent n is observed to be 4, while the apparent activation energy Q is 193±19 kJ/ mol .