Grain boundary role in the electrical properties of La1-xSrxCo0.8Fe0.2O3-δ perovskites

The electrical properties of mixed-conducting perovskite La1-xSrxCo0.8Fe0.2O3-delta samples have been studied as function of composition, temperature and bias conditions. Attention is focused on the investigation of the grain boundary role in the conductivity reduction. Impedance spectroscopy and I-V characteristics are applied to observe the behaviour of the perovskite samples. Sr-substitution leads to an increase of the electronic conductivity of the samples and reduction of the E-a value. It was established that the samples possess a typical semiconductor-like behaviour. The impedance spectra show that the charge carriers can be divided into two different categories: those which are blocked and those which are non-blocked by grain boundary related processes. In an attempt to discuss the formation and effect of depletion zones at grain boundaries, a model of back-to-back double Schottky barriers is suggested. It was shown that the grain boundaries have an influence (in our case a decrease of conductivity) on electrical properties in perovskite electronic ceramics. It was confirmed that the dielectric constant values decrease with increase of the frequency. (C) 1998 Elsevier Science B.V. All rights reserved.