The reaction between lanthanum oxide and strontium carbonate was studied non-isothermally between 350 and 1150 degrees C at different heating rates, intermediates and the final solid product were characterized by X-ray diffractometry (XRD). The reaction proceeds through formation of lanthanum oxycarbonate La2O(CO3)(2), lanthanum dioxycarbonate La2O2CO3, and non-stoichiometric strontium lanthanum oxide La2SrOx (x = 4 + delta). La4SrO7 was found to be the final product which begins to form at similar to 700 degrees C. Li+ doping enhances the formation of the final product as well as commencement of the reactions at lower temperatures. (c) 2006 Elsevier B.V. All rights reserved.