The electrical properties of zinc oxide varistor ceramics and PTC-type barium titanate ceramics were theoretically traced back to potential barriers at the grain boundaries. These barriers were supposed to originate from specific concentration profiles of intrinsic vacancies. Calculations of these profiles were missing up to the present, although this would essentially contribute to a better understanding of the electrical properties of these ceramics. Such numerical calculations were performed and the results were reported. Computations of the profiles in ZnO-ceramics of different compositions yield that the varistor effect could not merely be explained by a tunnelling process as was usually done in the literature. Moreover, it was possible to calculate the potential barrier width in BaTiO3 ceramics in dependence on sintering parameters. The calculated values were in good agreement with experimental results. Existing theories were verified and extended.

Vacancy Diffusion Profiles at the Grain Boundaries of Electronic Ceramics. Köhler, D., Koschek, G., Kubalek, E.: Physica Status Solidi A, 1988, 105[2], 377-85