Internal Activation Strain and Oxygen Mobility in a Thermally Stable Layered Fe3+ Oxide

The behavior of the layered Fe3+ perovskite superstructure with composition Ba1.7Ca2.4Y0.9Fe5O13 (BCYF) as an intermediate temperature solid oxide fuel cell (IT-SOFC) cathode is investigated by an integrated modeling, secondary ion mass spectroscopy (SIMS), processing, and electrochemistry approach. Electronic structure calculations identify the defect chemistry and energetics of the multiple diffusion pathways possible in the superstructure. This reveals a wide distribution of activation energies with the favorable pathways corresponding to transport along the layers. In contrast, interlayer oxygen transport paths require higher activation barriers, whose limiting step corresponds to incorporation of oxide ion vacancies in the Ca2Fe2O5 sub-block of the structure with tetrahedrally coordinated Fe3+ ions, with a calculated activation barrier of 1.46 eV. The latter is similar to the diffusion barrier of 1.41 eV evaluated by direct SIMS measurement on polycrystalline BCYF samples. The experimentally determin...