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 res istances (R-B and R-gb) Of undoped strontium titanate ceramics in air and i n N-2. The high frequency contribution of the spectra does not depend signi ficantly on the average grain size or grain size distributions, and was thu s ascribed to the bulk behaviour. The grain boundary results obtained for s everal samples vary with the average grain size, and these effects nearly a gree with predictions by a simple brick layer model. The deviations from th is model may increase with decreasing temperature, and are somewhat greater in N-2 than in air. (C) 2000 Elsevier Science Ltd. All rights reserved.