A simple approach to oxide varistor materials

An approach for current-voltage characteristics (CVC) with natural nonlinearity parameter which could reflect the main aspects of the non-ohmic conduction in varistor ceramics was analyzed. Varistor ceramics consist of highly conductive grains with grain-boundary potential barriers formed during sintering. In a grain-boundary controlled non-Ohmic material the current density increment consist of two parts. One is due to the increment of electric field at constant conductivity and other reflects the conductivity increase due to a barrier height lowering. It can be proportional to the current density and to the increment of electric field and the conductivity of low-voltage varistor is increased with electric filed more strongly than the conductivity of high-voltage varistor. It was observed that the increase in low-voltage resistors at low fields is due to a relatively small number of key barriers connected in series along the percolation path.