THE COMPLEX PEROVSKITE-RELATED SUPERSTRUCTURE BA2FE2O5 SOLVED BY HREM AND CIP

Barium ferrite Ba2Fe2O5 is a complex perovskite-related structure. The crystal is monoclinic P2(1)/c, with a = 6.969(l), b = 11.724(1), c = 23.431(5) angstrom, beta = 98.74(l)-degrees. 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 [476BAR]m (corresponding to [101]c of perovskite).