This study examines high temperature carbon dioxide permeation properties and long-term permeation stability of samarium doped ceria (SDC)-carbonate dual-phase membranes. Hermetic SDC-carbonate membranes were prepared by infiltrating porous SDC ceramic support with Li/K/Na molten carbonate. Carbon permeation experiments on the SDC-carbonate membranes were conducted with either atmospheric or high pressure feed of CO2:N-2 mixture or simulated syngas with composition of 50% CO, 35% CO2,10% H-2, and 5% N-2. The SDC-carbonate membranes exhibit CO2 permeation flux in the range of 02-0.8 mL(STP) cm(-2) min(-1) in 700-950 degrees C with measured CO2 to N-2 separation factor above 1000. The CO2 permeation flux shows power function dependence with CO2 partial pressure and exponential dependence with temperature. The activation energy for CO2 permeation is 63 kJ mol(-1), similar to that for oxygen ionic conduction in SOC. Essentially the same CO2 permeation characteristics are observed for the membranes with CO2:N-2 and simulated syngas feeds. The membranes exhibit stable long-term permeation flux in 700-900 degrees C with either CO2:N-2 or simulated gas feed at atmospheric pressure or high pressure (5 atm) for various periods of testing time (as long as 35 days). The membranes, with remarkable permeation stability in the presence of H-2, show only slight decomposition of the ceramic phase after long-term exposure to feed gas mixtures at high temperature. (C) 2014 Elsevier B.V. All rights reserved.