Microstructure and ionic conductivity of strontium-substituted lanthanum cobaltites

La_0.4Sr_0.6CoO_3-δ powders were synthesized by the glycine nitrate process. X-ray powder diffraction and selected area electron diffraction (SAED) in the transmission electron microscope (TEM) were used to determine the basic crystal structure of the perovskite samples. Additionally, energy-filtering transmission electron microscopy (EFTEM) was used to evaluate the homogeneity of the samples at the nanometer level. The ionic conductivity σ_i of La_0.4Sr_0.6CoO_3-δ was obtained from galvanostatic polarization experiments as a function of oxygen non-stoichiometry for 3-δ values between 2.70 and 2.81 (corresponding to p_O2 values between 10^-4 and 10^-1 bar) at 775 and 825 °C. It could be observed that σ_i shows a maximum which shifts towards larger values of the oxygen non-stoichiometry with increasing temperature. The maximum value was observed at 3-δ=2.79 and 2.77 for 775 and 825 °C, respectively. This behavior has been reported to be indicative of the formation of vacancy-ordered structures which are expected to lower the mobility of oxygen vacancies. The TEM investigations revealed a superstructure within microdomains which were crystallographically oriented perpendicular to each other and were found to be around 100 nm in size.