The O flux through dense membranes with the compositions, SrFeO3-δ, SrFe0.67Co0.33O3-δ and Sr0.97Fe0.33Co0.67O3-δ (0, 33% and 67%Co), were measured at 1000C as a function of the membrane thickness; with synthetic air on the primary side and He on the secondary side. The maximum flux rate was found to increase with Co content, with an observed maximum for a membrane with a composition 67%Co and a thickness of 0.5mm, corresponding to 3.8 x 10-6mol/cm2s. Based upon the experimental data, the critical thickness was estimated to decrease from 2.0mm for SrFeO3-δ to 0.7 mm for a compound with 67%Co added. A marked O flux reduction was observed below about 900C for membrane samples with the composition Sr0.97Fe0.33Co0.67O3-δ; corresponding to a transition from a cubic perovskite, with disordered O vacancies, to a rhombohedral brownmillerite structure with ordered O vacancies.

Oxygen Permeation in the System SrFeO3-x–SrCoO3-y. K.Wiik, S.Aasland, H.L.Hansen, I.L.Tangen, R.Ødegård: Solid State Ionics, 2002, 152-153, 675-80