La0.4Sr0.6CoO3-delta 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 sigma(1) of La0.4Sr0.6CoO3 -sigma was obtained from galvanostatic polarization experiments as a function of oxygen non-stoichiometry for 3 - sigma values between 2.70 and 2.81 (corresponding to p(O2) values between 10(-4) and 10(-1) bar) at 775 and 825 degreesC. It could be observed that sigma(i) shows a maximum which shifts towards larger values of the oxygen non-stoichiometry with increasing temperature. The maximum value was observed at 3 - sigma = 2,79 and 2.77 for 775 and 825 degreesC, 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.