A novel CO2-tolerant alkaline-earth metal-free single phase membrane based on (Nd0.9La0.1)(2)Ni0.74Cu0.21Ga0.05O4+delta (NLNCG) was successfully prepared though a sol gel route. The oxygen permeation and the stability of the NLNCG under CO2 are investigated in detail At 975 degrees C, when helium is used as the sweep gas, the oxygen permeation flux of 0.53 ml/min cm(2) (STP) is obtained. When the sweep gas is changed from helium to CO2, the oxygen permeation flux is reduced to OAR ml/min cm(2) (STP). Only a slight decrease of the oxygen permeation flux through the NLNCG membrane is observed. During the 420 h operation with CO2 as the sweep gas at 975 degrees C, a steady oxygen permeation flux through the NLNCG membrane of 0.53 ml/(min cm(2)) is obtained. From XRD and SEM characterizations, it is found that the spent membrane still maintains the perfect K2NiF4-type phase structure and intact microstructure without any carbonate indicating that the NLNCG membrane shows an excellent stability under CO2 atmosphere. (C) 2013 Elsevier Ltd. All rights reserved.