title: Triclinic crystal structure distortion of multiferroic BiMn7O12.
abstract: The quadruple perovskite BiMn7O12obtained via high-pressure synthesis was investigated by high-resolution synchrotron X-ray powder diffraction over a temperature range of 10 to 295 K. Careful Rietveld analysis reveals triclinic lattice distortion of BiMn7O12at 295 K, which increases upon cooling to 10 K. Also hkl-dependent anisotropic Bragg reflection shape was introduced to give a precise description of the diffracted intensities. Importantly BiMn7O12crystal structure was described in the non-centrosymmetric I1 triclinic space group. We also demonstrate the use of irreducible representations analysis (ISODISTORT program) for crystal structure distortion from Im to I1 space group. The irreducible representation which describes crystal structure distortion points towards possible ferroelectricity. Finally anisotropic thermal lattice expansion was observed.
authors.affiliation: Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, PO Box 1033, N-0315 Oslo, Norway.
authors.forename: Wojciech A
authors.initials: WA
authors.lastname: Sławiński
authors.affiliation: Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, PO Box 1033, N-0315 Oslo, Norway.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Okamoto
authors.affiliation: Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, PO Box 1033, N-0315 Oslo, Norway.
authors.forename: Helmer
authors.initials: H
authors.lastname: Fjellvåg
keywords: ISODISTORT; X-ray diffraction; anisotropic peak shape; multiferroic material; triclinic perovskite