Variations in microstructural development and in the electrical properties of SnO2-based varistors were considered on the basis of the O vacancies created or annihilated by the presence of different additives. Electron paramagnetic resonance analysis of sintered samples revealed a substantial increase in the paramagnetic O vacancy concentration when Nb2O5 was added to the SnO2▪Co3O4 system. On the other hand, an observed diminution in the concentration of such species after adding Fe2O3 indicated solid solution formation. The quantification of paramagnetic O vacancies confirmed that substitutions took place in the lattice during sintering. These findings were supported by scanning electron microscopy, by density measurements and by current density versus electric field curves.

The Role of Oxygen Vacancies on the Microstructure Development and on the Electrical Properties of SnO2-Based Varistors. R.Parra, C.M.Aldao, J.A.Varela, M.S.Castro: Journal of Electroceramics, 2005, 14[2], 149-56