Effect of Cr$_{2}$O$_{3}$ on the microstructure and non-ohmic properties of (Co, Sb)-doped SnO$_{2}$ varistors

Abstract

The effect of Cr$_{2}$O$_{3}$ addition on the physical characteristics, microstructure, and current-voltage properties of (Co-Sb)-doped SnO$_{2}$ varistors was investigated. SnO$_{2}$-Co$_{3}$O$_{4}$-Sb$_{2}$O$_{5}$ ceramics with additions of 0.0, 0.03, 0.05 and 0.07 mol % Cr$_{2}$O$_{3}$ were sintered at 1350 $^{o}$C under ambient atmosphere and characterized microstructurally and electrically. The characterization by XRD and SEM show that the microstructure remains as a single phase material with multimodal size distribution of SnO$_{2 }$grains. The greatest effect of Cr$_{2}$O$_{3 }$additions is manifested in the electric breakdown field. Additions of high levels (0.07 and 0.05 %) of this oxide promote an increase of approximately 55% in this parameter compared to the Cr$_{2}$O$_{3}$-free sample. Another physical property is affected: the measured density values decreases as the Cr$_{2}$O$_{3}$ content increases. A change in the nonlinearity coefficient value is produced only at the highest Cr$_{2}$O$_{3}$ content while at intermediate levels there is not change at all. Consequently, when seeking high nonlinearity coefficients, intermediate levels of Cr$_{2}$O$_{3}$ are not recommended.