Compounds with the general formula La0.8Sr0.2Cu1-xMnxOy were prepared by the citrate route for use in solid oxide fuel cells (SOFCs). A solid solution region containing hexagonal perovskite phase was formed when 0.6 <= x <= 1, in which the oxygen content in air changes from oxygen stoichiometry to oxygen excess with Mn doping. The temperature dependence of electrical conductivity changes from metallic-like behavior in La0.8Sr0.2CuO2.49 to semiconducting type in La0.8Sr0.2MnO3.08. Mn doping resulted in a decrease in the conductivity (with the minimum at 40% Mn doping), whereas the thermal expansion coefficient decreased linearly with x. A defect model for the mixed Cu-Mn perovskite is proposed and related to its physical and electrochemical properties. (c) 2007 The Electrochemical Society.