Effect of Ca, Sr and Ba on the structure, morphology and electrical properties of (Co,Sb)-doped SnO2 varistors

In this work, the effect of calcium (Ca), barium (Ba) and strontium (Sr) additions on the microstructure and electrical properties of SnO2-Co3O4-Sb2O5 ceramic varistors was investigated. It was found that the calcium addition promotes densification and grain growth. Ceramics with calcium addition exhibit the lowest electric field at a fixed current density (10−3 A cm−2). The addition of strontium shows a similar effect on microstructure and current-voltage characteristics. However, barium addition causes porosity increase, grain size reduction, changes in the grain morphology (from approximately equiaxed to elongated grains) and the electric field at a fixed current density showed almost no change. Consequently, Ba-containing SnO2-based ceramics cannot be considered as attractive candidates for low-voltage varistors.