New composite materials with mixed oxygen ionic and electronic conductivity based on perovskite SrTi0.5Fe0.5O3 - delta and fluorite Ce-0.8(Sm0.5Sr0.2)(0.2)O2 - delta were prepared by mixing base components synthesized by the solid state reaction method with following joint calcination at 1573 K and sintering in a gas-tight ceramic at 1623-1823 K. The phase content, microstructure and surface morphology, thermal expansion of sintered samples and their electrical properties were investigated by XRD, scanning electron microscopy, dilatometric method and four-probe dc technique, respectively. It was found that the composite materials are two-phase perovskite-fluorite systems with chemically stable content, characterized by the smallness of grain size relative to Ce-0.8(Sm0.5Sr0.2)(0.2)O2 - delta and considerably higher microhardness in comparison with SrTi0.5Fe0.5O3 - delta. They possess intermediate values of thermal and chemical expansion, and high level of ionic and n-type electronic conductivity, making these composite materials promising candidates as mixed ionic and electronic conducting ceramic membranes for a wide variety of gas separation applications, including oxygen separation, partial oxidation of methane and hydrogen separation and as anodes for solid oxide fuel cells (SOFCs). (C) 2013 Elsevier B.V. All rights reserved.