Structural Stability and Oxygen Permeation Properties of Sr[sub 3−x]La[sub x]Fe[sub 2−y]Co[sub y]O[sub 7−δ] (0≤x≤0.3 and 0≤y≤1.0)

The structural stability and oxygen permeation properties of Sr 3 − x La x Fe 2 − y Co y O 7 − δ with 0 ⩽ x ⩽ 0.3 and 0 ⩽ y ⩽ 1.0 have been studied at high temperature ( 800 ⩽ T ⩽ 900 ° C ) and in the oxygen partial pressure range 10 − 5 ⩽ p O 2 ⩽ 0.21 atm. These phases have a perovskite-related intergrowth structure with tetragonal symmetry, which does not change with temperature up to 1000°C in the range 10 − 5 ⩽ p O 2 ⩽ 0.21 atm. The oxygen permeation flux of Sr 3 − x La x Fe 2 − y Co y O 7 − δ 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 Sr 2.7 La 0.3 Fe 1.4 Co 0.6 O 7 − δ at 900°C indicates the oxygen transport is bulk limited for this composition. Assuming that this observation is also valid for other compositions, the ionic conductivity, σ i , and the vacancy diffusion coefficient D v have been estimated. The structural stability and permeation properties of Sr 3 − x La x Fe 2 − y Co y O 7 − δ are compared with those of the perovskite phases SrFe 0.2 Co 0.8 O 3 − δ and Sr 0.6 La 0.4 Fe 0.2 Co 0.8 O 3 − δ .