Effect of sintering temperature on the electric properties and microstructure of SnO2-Co3O4-Sb2O5-Cr2O3 varistor ceramic

SnO2 varistors doped with Co3O4, Cr2O3, and Sb2O5 were prepared by a high-energy milling planetary method. The sintering temperature of the varistors was optimized to improve the electrical properties, nonlinearity coefficient and breakdown electric field. The best results were achieved at a sintering temperature of 1350 degrees C, obtaining a nonlinear coefficient of 33 and a breakdown electric field of 2620 V cm(-1). The samples obtained at all sintering temperatures showed not only high density values, reaching 90.5% of the theoretical density, but also the resulting microstructure was optimized in such a way that the varistors compete with those obtained by chemical methods, with the advantage that the milling planetary method is cheaper, faster and easier than chemical routes. Based on substitution equations using the Kroger-Vink standard notation, an attempt is made elucidate the role of each of the dopants. A processing-microstructure-property correlation is also reasonably established. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.