Effect of inner strain on the performance of dual-phase oxygen permeable membranes

Abstract Inner strain appears in the dual-phase composites due to the different thermal expansion coefficients (TECs). For fluorite and perovskite epitaxial growing films, tensile and compressive strains can promote and inhibit the oxygen ionic transport, respectively. For oxygen permeable membranes, the oxygen ionic transport is closely related to the oxygen permeation flux. Therefore, the inner strain would affect the performance of fluorite-perovskite dual-phase membranes, however, that is still not disclosed. Herein, we found that the fluorite phase with low TECs is slightly stretched and the perovskite phase with high TECs is compressed in dual-phase membranes. The inner strain inhibits chemical expansion of perovskite phase by limiting the redox of B-site cations. Although the perovskite single-phase has the highest oxygen permeation flux, the oxygen permeation flux of dual-phase membranes decreases with increasing the content of perovskite phase. The unusual phenomenon is induced by the compressive strain on perovskite phase limiting the transport of oxygen ions. Therefore, in view of the vital role of inner strain to the chemical expansion and oxygen transport, it cannot be ignored during the design and mechanism discussion of oxygen permeable membranes.