Triclinic crystal structure distortion of multiferroic BiMn7O12

Abstract

The quadruple perovskite BiMn7O12obtainedviahigh-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. Alsohkl-dependent anisotropic Bragg reflection shape was introduced to give a precise description of the diffracted intensities. Importantly BiMn7O12crystal structure was described in the non-centrosymmetricI1 triclinic space group. We also demonstrate the use of irreducible representations analysis (ISODISTORTprogram) for crystal structure distortion fromImtoI1 space group. The irreducible representation which describes crystal structure distortion points towards possible ferroelectricity. Finally anisotropic thermal lattice expansion was observed.