Grain refinement and non-ohmic properties in (Co, Ta)-doped SnO 2 ceramics by Cr 2 O 3 additions and the in situ formation of CoCr 2 O 4

In this investigation, the microstructure and current–voltage properties of (Co, Ta)-doped SnO2 ceramics were found to depend on Cr2O3 additions. SnO2–Co3O4–Ta2O5 ceramics with additions of 0, 0.05, 0.1, 1 and 2 mol% Cr2O3 were sintered at 1350 °C under an oxidizing atmosphere and characterized microstructurally and electrically. Characterization by XRD and SEM shows that for samples with 0–1.0 mol% Cr2O3, the microstructure consists of single-phase SnO2 grains, while for the sample with the highest Cr2O3 content, the CoCr2O4 spinel phase is present in SnO2 microstructure. Moreover, reduced grain size distribution breadth and average grain size are observed in the SnO2 microstructure with 2 mol% Cr2O3. Results suggest that nonlinearity coefficient (α) is not as sensitive as electric field at fixed current density (EB) to Cr2O3 concentration changes.