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

Abstract

The effect of CaO through additions of CaCO$_{3}$ 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 0.1, 0.5 and 1 mol % CaO were sintered at 1450$^{\circ}$C under oxidizing atmosphere and characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Results show that, at low and intermediate CaO levels, density is not significantly influenced, whilst at the highest level, density decreases substantially. The nonlinear coefficient and the breakdown voltage behave similarly in one sense because both present a maximum, and because at the highest CaO level, both response variables show the lowest values. The nonlinear coefficient presents a maximum of 12.9 at 0.1 mol % CaO, while the same maximum for the breakdown voltage occurs at 0.5 mol % CaO. At 1 mol % CaO, the breakdown voltage is 288 Vcm$^{ - 1}$.