Effects of Sb and Nb dopants on electrical and microstructural properties of low-voltage varistor ceramics based on SnO2

It is shown that an addition of Sb2O5 or Nb2O5 (0.05-0.15 mol%) to the system SnO2-CoO-Cr2O3-Bi2O3 leads to the enhancement of grain growth. This effect is associated with the presence of the liquid Bi-phase in ceramics during sintering. The obtained ceramics possess non-linear current-voltage characteristics and can be used for preparing low voltage varistors. The non-linearity coefficient α reaches 22 and the characteristic electric field 692 V/cm for Nb-doped materials and 11 and 421 V/cm respectively for Sb-doped ceramics materials. The results of dc and ac electrical measurements, as well as scanning electron microscopy are presented and discussed in terms of the known barrier model for varistors.