Characterisation of SnO2–CoO–MnO–Nb2O5 ceramics

Varistors based on SnO2 have attracted increasing interest in recent years. However, the combined effect of CoO–MnO on SnO2 ceramics is still unclear. In this study, the non-Ohmic behaviour of the 98.95 mol%SnO2–0.5 mol%CoO–0.5 mol%MnO–0.05 mol%Nb2O5 system, the microstructures and the influence of sintering temperature were investigated. The samples were prepared by the mixed oxide route, and were sintered at temperatures in the range 1250–1450 °C. SEM observation and EDS analysis revealed that the ceramics have a two-phase microstructure comprising SnO2 primary grains and a Mn, Co rich secondary phase of small particles. The sintered density of the samples increased with the increase in sintering temperature. The maximum non-linear coefficient (α = 10) was obtained at a sintering temperature of 1350 °C.