Role of perovskite phase on the oxygen permeation properties of the Sr4Fe6-xCoxO13+delta system

Oxygen permeation measurements of the Sr4Fe6-xCoxO13+delta system with 0 le ss than or equal to x less than or equal to 2.0 an presented. Sr4Fe6-xCOxO1 3+delta samples prepared by solid-state method consist of single-phase Sr4F e6-xCoxO13+delta for 0 less than or equal to x < 1.5 and a three-phase mixt ure composed of the intergrowth phase Sr4Fe6-xCoxO13+delta with x < 1.5, th e perovskite phase SrFe1-xCoxO3-delta, and the spinel phase Co3-xFexO4 for 1.5 less than or equal to x less than or equal to 2.0. On the other hand, S r4Fe6-xCoxO13+delta samples prepared by a sol-gel method consist of single- phase Sr4Fe6-xCoxO13+delta for the entire 0 less than or equal to x less th an or equal to 2.0. The Sr4Fe4Co2O13+delta composition consisting of the th ree-phase mixture exhibits oxygen permeation fluxes one order of magnitude higher than the single-phase Sr4Fe4Co2O13+delta. The higher oxygen permeati on rate of the sample consisting of three phases is due to the perovskite p hase since single-phase perovskite SrFe0.75Co0.25O3-delta permeates oxygen two orders of magnitude higher than the single-phase Sr4Fe4CO2O13+delta. Wh ile the single-phase Sr4Fe6-xCoxO13+delta samples shaw stable oxygen permea tion rates as a function of rime, the Sr4Fe6-xCoxO13+delta samples consisti ng of the three-phase mixture show a decrease in oxygen permeation with lim e. (C) 2000 The Electrochemical Society. S0013-4651(99)09-055-2. All rights reserved.