Grain size dependent electrical conductivity, chemical surface exchange and bulk diffusion coefficient of La0.5Sr0.5Al0.2Fe0.8O3-δ

Abstract Electrical conductivity, chemical bulk diffusion coefficient (Dchem), and surface exchange coefficient (Kchem) of La0.5Sr0.5Al0.2Fe0.8O3-δ (LSAF) perovskite were investigated as a function of grain size. The grain size of the sintered LSAF samples was varied in the range 0.65–6.12 μm on tailoring the sintering profile in the temperature range 1150–1450 °C for a duration of 2–8 h. The sample showed metallic conductivity in the high-temperature region and also exhibited conductivity hysteresis while measured on heating and cooling. The electrical conductivity of the sample measured at 850 °C exhibited a nonlinear dependence with grain size wherein conductivity increases initially with the grain size and then decreased. It was found to vary in the range 91.85–163.28 S cm−1 measured at 850 °C depending on the grain size. Electrical conductivity relaxation (ECR) spectra do not trace back on oxidizing and reducing conditions. The values of Kchem and Dchem calculated from ECR spectra were found to vary between 1.34 × 10−3 cm s−1 to 2.39 × 10−3 cm s−1 and 1.99 × 10−5 cm2 s−1 to 3.42 × 10−5 cm2 s−1 respectively in the studied temperature zone and grain size. The observed experimental data were correlated with the microstructure and defect chemistry of the sample.