Impedance spectroscopy of Sr0.97Ti1-xFexO3-delta materials with moderate Fe-contents

Complex impedance spectroscopy was used to characterize the electrical beha vior of polycrystalline Sr0.97Ti1-xFexO3-delta materials. The impedance plo ts obtained for samples with x greater than or equal to 0.07 (7%Fe or highe r) did not reveal a resistive grain boundary contribution, thus suggesting a major change in grain boundary dispersion (relative to samples with small Fe contents). The dielectric constant remains nearly independent of the Fe content, and is close to the dielectric constant of strontium titanate sin gle crystals. SEM microstructures reveal a remarkable change in grain growt h behaviour. Ceramic samples with x greater than or equal to 0.07 show aver age grain sizes in the range 0.3-2 mum, which is much smaller than found fo r samples with up to 5% Fe or lower Fe contents. The bulk conductivity incr eases rapidly with the Fe content, mainly due to a decrease in activation e nergy, The bulk conductivity results deviate from a typical Arrhenius law, and suggest a transition towards a variable range hopping mechanism at room temperature or lower. (C) 2001 Elsevier Science B.V, All rights reserved.