Crystal phase analysis of SnO2-based varistor ceramic using the Rietveld method

A second addition of l mol% of CoO to a pre calcined SnO2-based ceramic doped with 1.0 mol% of CoO, 0.05 mol% of Nb2O5 and 0.05 mol% of Cr2O3 promotes the appearance of a secondary phase, Co2SnO4, besides the SnO2 cassiterite phase, when the ceramic was sintered at 1350 °C/2 h. This was observed using X-ray powder diffraction, scanning electron microscopy and energy dispersive X-ray techniques. Rietveld refinement was carried out to quantify the phases present in the ceramic system. The results of the quantitative analysis were 97 wt.% SnO2 and 3 wt.% Co2SnO4. The microstructural analysis showed that a certain amount of cobalt ion remains into cassiterite grains.