Structural Stability and oxygen permeation properties of Sr3-xLaxFe2-yCoyO7-δ (0 ≤ x ≤ 0.3 and 0 ≤ y ≤ 1.0)

The structural stability and oxygen permeation properties of Sr3-xLaxFe2-yCoyO7-delta with 0 less than or equal to x less than or equal to 0.3 and 0 less than or equal to y less than or equal to 1.0 have been studied at high temperature (800 less than or equal to T less than or equal to 900 degreesC) and in the oxygen partial pressure range 10(-5) less than or equal to pO(2) less than or equal to 0.21 atm. These phases have a perovskite-related intergrowth structure with tetragonal symmetry, which does not change with temperature up to 1000 degreesC in the range 10(-5) less than or equal to pO(2) less than or equal to 0.21 atm. The oxygen permeation flux of Sr3-xLaxFe2-yCoyO7-delta membranes increases with increasing Co content, decreases with increasing lanthanum content, and does not change with time. Measurements of oxygen permeation flux as a function of membrane thickness for Sr2.7La0.3Fe1.4Co0.6O7-delta at 900 degreesC indicates the oxygen transport is bulk limited for this composition. Assuming that this observation is also valid for other compositions, the ionic conductivity, sigma (1), and the vacancy diffusion coefficient D-v have been estimated. The structural stability and permeation properties of Sr3-xLaxFe2-yCoyO7-delta are compared with those of the perovskite phases SrFe0.2Co0.8O3-delta and Sr0.6La0.4Fe0.2Co0.8O3-delta. (C) 2001 The Electrochemical Society.