The purpose of this study is to determine the solid state reactions leading to the formation of La0.6Sr0.4Co0.8Fe0.2O3 and La0.6Sr0.4Co0.2Fe0.8O3 which are widely used as cathode material in solid oxide fuel cells (SOFC) from precursor salts. Interactions between the cathode and the electrolyte layers are also investigated while the cathode layer formed upon heating in contact with the surface of cerium -gadolinium oxide (CGO) electrolyte substrates. Almost all combinations of precursor salt mixtures were tested to see if all solid state reactions are completed and what phases eventually formed. Most of the transformation was complete after 1050 degrees C heat treatment to yield different mixed oxides. The cathode layer was usually in porous form but was found to spread well over the substrate. Uneven diffusion of La, Sr, Co or Fe into the substrate influenced the stoichiometry of the resulting cathode layer in varying degrees. Fe was found to diffuse into the substrate. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.