Non-ohmic conduction in tin dioxide based ceramics with copper addition

The current-voltage characteristics and temperature dependences of electrical conductivity in SnO2-Co3O4-Nb2O5-Cr2O3-CuO semiconductor ceramics are studied, and possible mechanism of non-ohmic conduction in these materials is discussed. Due to addition of CuO up to 0.5 mol.%, the nonlinearity coefficient is increased up to 75, and the electric field is decreased down to 3900 V.cm(-1) (at 1 mA.cm(-2)). It makes CuO addition useful for the preparation of SnO2-based varistors. It is concluded that the electrical conduction is controlled by grain-boundary barriers. The activation energy of electrical conduction E-sigma (the barrier height phi) is decreased with an increase in the electric field E. The higher slope of the E-sigma(E) dependence at high fields can be related to a participation of minority carriers (holes). The addition of more than 0.5 mol.% CuO leads to degradation of the varistor effect due to percolation via quite conductive CuO-based intergranular phase.