The Random Barrier Model and the Resistance Anomalies in Ferroelectric Ceramics

The theory of the low-and high field conductivity of ferroelectric ceramics in the region of the positive temperature coefficient of the resistivity (PTCR) is reformulated on the basis of the random barrier model. For the low-field conductivity the model gives the temperature dependence of the conductivity essentially similar to that which follows from the Heywang equivalent-barrier model. The fluctuation of the barrier heights plays an important role for high fields where the shape of the current-voltage characteristic appears to be quite different from that given by the equivalent-barrier model. The experimental data on the high-field conductivity of (BaCe)TiO 3 -ceramics are in agreement with the predictions of the random barrier model.