DEPENDENCE OF THE GRAIN-BOUNDARY POTENTIAL BARRIER HEIGHT OF BATIO3 CERAMICS ON DONOR DOPANT CONCENTRATION

Barium titanate ceramics exhibiting the positive temperature coefficient of resistance (PTCR) effect were prepared with donor concentrations ranging from 0.05-1.8 at.%. The resistance of the various samples (normalised to give the specific resistance of a unit area of grain boundary rho Lin order to eliminate the effect of the observed reduction in grain size with increased donor concentration) was measured in the vicinity of the ferroelectric transition temperature Tc. Arrhenius plots of rho Lagainst (T- theta)/T, where T is the absolute temperature and theta is the Curie point, were then obtained for T<Tc. The plots were found to be linear up to a few degrees below the temperature corresponding to the maximum value of rho L, in agreement with the well known Heywang model. The potential barrier heights, calculated from the slopes of the Arrhenius plots, were found to be similar for samples containing 0.1-1.4 at.% (approximately 0.2 eV at 150 degrees C) and greater in more heavily doped specimens (0.4 eV at the same temperature). However, the Arrhenius plots belonging to samples containing 0.05 at.% were linear for a small temperature range since the PTCR jump was very small and consequently it was not possible to calculate the potential barrier height with any accuracy. © 1990 IOP Publishing Ltd.