Dual-phase membranes made of fluorite-type ionic conductors and perovskite-type mixed ionic-electronic conductors (MIEC) have attracted wide attentions in recent years. Here, we report dual-phase membranes, which are made of a ceria-based oxygen ionic conducting oxide (Ce0.8Sm0.2O1.9) and Ca-doped MIEC perovskite oxides (Sm0.6Ca0.4CoO3 (delta) and Sm0.6Ca0.4FeO3 (delta)), and show high structural stability and permeation fluxes. The cobalt- and iron-containing dual-phase membranes were comparatively investigated to find the dependence of the dual-phase membrane properties, such as membrane microstructure, conductivity, oxygen flux as well as stability under a CO2 environment, on B-site elements (Co and Fe) of perovskite phase. It is found that the weight ratio of Sm0.6Ca0.4CoO3-delta, phase should be no less than 33 wt%; otherwise, the electronic conductivity of the corresponding dual-phase membranes is insufficient for oxygen permeation. However, a lower weight ratio (25 wt%) of Sm0.6Ca0.4FeO3-delta phase offers sufficient electronic conductivities for oxygen permeation through the dual-phase membranes. The significant difference in the minimum weight ratio of the two perovskite phases in dual-phase membranes results from the different microstructures developed during the high-temperature sintering process. All the dual-phase membranes are stable under CO2 sweep and show high oxygen permeation flux up to 0.55 mL cm(-2) min(-1) at 950 degrees C through 0.5 mm thick membranes. (C) 2014 Elsevier B.V. All rights reserved.