For application in solid oxide fuel cells La0.8Sr0.2CuO2.4+delta was synthesized and the phase evolution-was characterized after quenching from different temperatures and after slow cooling. A single phase perovskite was found after quenching from 950 degrees C. The electrical conductivity of the La0.8Sr0.2CuO2.4+delta perovskite exhibited metallic behavior reaching values of about 270 S/cm at 800 degrees C in air. The thermal expansion between 30 and 800 degrees C gave a thermal expansion coefficient of 11.1 x 10(-6) K-1. At higher temperatures, the perovskite was transformed to the K2NiF4-type structure via an intermediate stage that can be best described as a LaSrCuO4 phase with preferential growing of {020} lattice planes. After sintering at 1100 degrees C and slow cooling in the furnace a phase mixture of (La,Sr)CuO4+delta and (La,Sr)CuO2.4+delta perovskite was obtained. This phase mixture showed higher electrical conductivity (400 S/cm at 800 degrees C) and smaller thermal expansion coefficient (9.6 x 10(-6) K-1) than the single phase La0.8Sr0.2CuO2.4+delta perovskite. (c) 2006 Elsevier B.V. All rights reserved.