In this paper the results of thermal expansion coefficient measurements of different singly and doubly doped ceria electrolytes, together with results for selected cathode materials from (La,Sr)(Co,Fe,Ni)O-3 system are given. A high temperature chemical stability of the cathode-electrolyte interface was measured on 1:1 wt. mixtures of previously characterized ceria and perovskite powders. The samples were heated at 800, 1000 or at 1200 degrees C in air for 6 or 100h. Chemical reactivity investigations were conducted using XRD with Rietveld analysis. For all heated samples the crystal structure of both components were preserved. However, their lattice parameters evolved to a different extent, suggesting the existence of cation exchange. A formation of the solid state solution between Ce1-xRExO2-x/2 and La(Co,Fe,Ni)O3-delta was found, with mobile La cation. On the basis of the obtained results a qualitative mechanism of the observed reaction was proposed. (c) 2007 Elsevier B.V. All rights reserved.