Characteristics of SnO2-doped ZnO-based varistor ceramics

The Sb2O3 in a ZnO-based varistor composition was systematically substituted with SnO2 in the range from 0 to 100%. The microstructural characteristics, average grain size and the general phase composition of the samples were not influenced by the substitutions. In all the samples we observed ZnO, Bi2O3-rich and spinel phase, where the composition of the spinel depends on the Sb2O3 to SnO2 ratio in the starting composition. The non-linear coefficient α of the samples was not influenced by the SnO2 substitution, while the threshold voltage decreases and the leakage current increased with larger additions of SnO2. The capacitance–voltage measurements indicated strong increase in the donor density and the density of interface states at the grain boundaries while the depletion-layer width decreased and the barrier height was comparable in all the investigated samples. According to the electrical properties, SnO2 had a strong donor effect in the ZnO varistor ceramics.