Dense ceramic mixed ionic and electronic conducting membranes have been deposited by atmospheric spray-pyrolysis technique onto porous ceramic substrates. Perovskite oxide layers, i.e. manganites La1-xSrxMnPO3 ferrites La1-xSrxFe1-y(Co,Ni)(y)O-3, gallates La1-xSrxGa1-y (Co,Ni,Fe)(y)O-3, cobaltites La1-xSrxCoO3 and related perovskites such as lanthanum nickelate La2NiO4 layers have been prepared. The structure, morphology and composition of the layers were characterised by XRD, SEM and WDS, respectively. Density and gas tightness of the layers were studied as a function of deposition process parameters, film thickness (from similar to0.5 to similar to3 mum) and preparation procedure. The presence of cracks and defects due to thermo-mechanical stresses applied during or after the preparation process were correlated with the membrane composition and the corresponding thermal expansion coefficient differences between substrates and membranes. (C) 2004 Elsevier B.V. All rights reserved.