The temperature dependence of the grain-boundary potential barrier height, and of the conductivity across the grain-boundary space-charge depletion layer in acceptor-doped ceramics, was investigated by using a numerical simulation technique. The underlying model was that of a back-to-back double Schottky barrier at the grain boundary. An interpretation was offered in the form of a defect chemistry model for the bulk, and for the space-charge depletion layer which surrounded the grain-boundary core on both sides. The temperature behavior of the potential barrier at the grain boundary could be divided into 3 different regimes. These were a linear regime, followed by saturation and decreasing regimes. Two different spatial conductivity profiles at the grain boundaries were identified with 2 different characteristic thermal activation energies for the effective grain-boundary conductivity. The barrier height itself was not equal to the thermal activation energy of the effective grain-boundary conductivity. The electrical characteristics of the grain boundaries could be deliberately influenced by decorating the boundaries with suitable dopants.

R.Hagenbeck, R.Waser: Journal of Applied Physics, 1998, 83[4], 2083-92