Microstructure and electrical properties in SnO2 ceramics with sequential addition of Co, Sb and Ca

The effect of sequential additions of Co3O4, Sb2O5 and CaCO3 on the microstructure and electrical behaviour of SnO2-based ceramics was investigated. Although without conferring varistor properties, Co3O4 additions promote densification in the material. Successive addition of Sb2O5 provides the sample varistor properties but with low nonlinearity coefficient (alpha = 5.7) and high electric field (E-1 = 2022 V cm(-1)) at current density 10(-3) Acm(-3). Moreover, antimony oxide addition degrades the microstructure condition by inducing porosity. Subsequent addition of CaCO3 promotes densification and grain growth. However, it does not lead to the increase in the nonlinearity coefficient. It only lowers the electric field, thus making the material suitable for lower voltage applications. Observed significant increase in the relative dielectric permittivity up to a factor of about 60 and 200 in the cases of antimony or antimony and calcium addition to SnO2-Co3O4 (accompanied by the appearance of varistor effect) is due to the formation of barrier depletion layers at grain boundaries.