Dependence of the nonlinear electrical behavior of SnO2-based varistors on Cr2O3 addition

Tin dioxide varistors doped with CoO, ZnO, Ta2O5 and Cr2O3 were prepared by the mixed oxide method. Temperature dependent impedance spectroscopy revealed two different activation energies, one at low frequencies and the other at high frequencies. These activation energies were associated with the adsorption and reaction of O2 species at the grain boundary interface. We show that Cr2O3 improves the varistor properties, generating sites for the adsorption of O′ and O″ at the grain boundary region. The O′ and O″ defects are truly responsible for the barrier formation at the grain boundary interface.