Defect profile and microstructural development in SnO2-based varistors

The microstructural development and the stabilised valence of the ions added to SnO2 were analysed. Aiming at a better interpretation of the involved phenomena, the effects on grain growth, secondary phase formation and structure of adding Co3O4, ZnO, MnO2, Sb2O3, or Nb2O5 have been studied. We found that cobalt, zinc and manganese stabilise as Co+2, Zn+2 and Mn+2 in the lattice, favouring the oxygen vacancy apparition and then, the grain growth and the potential barrier formation. Sb2O3 or Nb2O5 reduces the total oxygen vacancy concentration and the grain growth. Sb2O3 addition favours the CoSnO3 particle formation and Nb2O5 favours the formation of particles with an intermediate composition between CoSnO3 and Co2SnO4 in systems with Co3O4. These particles could also control the sintering and grain growth rates.