Mixed conducting La1-xSrxCo1-yFeyO3-delta (LSFC) perovskites are promising materials for oxygen separation membranes at high temperatures. Gaslight 10-20 mu m-thick perovskite layers were produced by vacuum slip-casting and screen printing on different porous substrates, i.e. Ce0.8Gd0.2O1.9 (CGO), LSFC and composites of both. Some of the substrates are doped with cobalt for enhancing the mechanical stability and the shrinkage rate of the substrate. The manufacturing of the substrates and the different perovskitic asymmetric membranes are described in detail. The microstructure, the chemical compatibility between substrate and membrane, and the stability of the sintered layers were analyzed by scanning electron microscopy (SEM, EDX), SIMS and XRD at room temperature. Also the shrinking rates, surface smoothness, porosity and air permeance of the different substrate compositions are characterized. SEM analysis of the sintered top-layers showed a thickness of 10-20 mu m, only closed porosity after sintering at 1200 degrees C and an He-leak rate in the range between 10(-4) to 10(-6) mbar l s(-1) cm(-2). The thermal expansion coefficient and electrical conductivity of the membrane materials and the substrates are measured between 30 and 800 degrees C and oxygen flux measurements were carried out in the range 750-900 degrees C. (c) 2006 Elsevier B.V. All rights reserved.