Applicability of the brick layer model to describe the grain boundary properties of strontium titanate ceramics

Impedance spectroscopy was used to evaluate the bulk and grain boundary resistances (RB and Rgb) of undoped strontium titanate ceramics in air and in N2. The high frequency contribution of the spectra does not depend significantly on the average grain size or grain size distributions, and was thus ascribed to the bulk behaviour. The grain boundary results obtained for several samples vary with the average grain size, and these effects nearly agree with predictions by a simple brick layer model. The deviations from this model may increase with decreasing temperature, and are somewhat greater in N2 than in air.