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A series of novel dense mixed conducting ceramic membranes based on K2NiF4-type (La1-xCax)2 (Ni0.75Cu0.25)O4+δ was successfully prepared through a sol-gel route.Their chemical compatibility,oxygen permeability,CO and CO2 tolerance,and long-term CO2 resistance regarding phase composition and crystal structure at different atmospheres were studied.The results show that higher Ca contents in the material lead to the formation of CaCO3.A constant oxygen permeation flux of about 0.63 mL.min-1·cm-2 at 1173 K through a 0.65 mm thick membrane was measured for (La0.9Ca0.1)2 (Ni0.75Cu0.25)O4+δ,using either helium or pure CO2 as sweep gas.Steady oxygen fluxes with no sign of deterioration of this membrane were observed with increasing CO2 concentration.The membrane showed excellent chemical stability towards CO2 for more than 1360 h and phase stability in presence of CO for 4 h at high temperature.In addition,this membrane did not deteriorate in a high-energy CO2 plasma.The present work demonstrates that this (La0.9Ca0.1)2(Ni0.75Cu0.25)O4+δ membrane is a promising chemically robust candidate for oxygen separation applications.