The complex perovskite-related superstructure Ba₂Fe₂O₅ solved by HREM and CIP

Barium ferrite Ba₂Fe₂O₅ is a complex perovskite-related structure. The crystal is monoclinic P2₁/c, with a = 6.969 (1), b = 11.724 (1), c = 23.431 (5) Å, β = 98.74 (1)°. The composition of one unit cell is Ba₂₈Fe₂₈O₇₀. The structure was solved using a combination of high-resolution electron microscopy (HREM), crystallographic image processing (CIP) and electron diffraction. The structure can be described as a perovskite with 14 oxygen positions unoccupied with respect to the ABO₃ stoichiometry in the monoclinic unit cell. These positions can be identified from the potential map obtained by HREM and CIP. They form two linear groups. Seven of them lie on a line along [476]_m (corresponding to [110]_c of perovskite), while the seven other symmetry-related positions lie along [46]_m (corresponding to [101]_c of perovskite).

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