A model of non-Ohmic conduction in ZnO varistors

A simple phenomenological approach to non-Ohmic conduction in zinc oxide based varistors is suggested. The decrease of the barrier height on voltage is considered as a reason of varistor effect. This model gives the relationship between the current density j and the average electric field E in the form j = sigma E-o exp(alpha E), where the nonlinearity factor a is proportional to the rate of change of the barrier height on voltage alpha proportional to (-d phi/dU). The nonlinearity factor alpha or the normalized nonlinearity coefficient beta(E) = beta/E-1 congruent to alpha (E-1 is the electric field at fixed current density) can be used instead of the traditional but empirical nonlinearity coefficient beta = (E/j)(dj/dE). Fairly reasonable agreement between suggested model and experimental results is found.