High-temperature phases of multiferroic BiFe0.7Mn0.3O3

We report the results of a high-resolution powder neutron-diffraction study of multiferroic BiFe0.7Mn0.3O3. We have confirmed the previous assignment of the ? phase and ? phase as having R3c and Pbnm symmetry, respectively. The ? phase, however, has been shown unequivocally not to be cubic, as previously reported, but rather to retain octahedral tilting distortions leading to a lower symmetry, most likely rhombohedral with space group R3Cc The ? phase of BiFe 0.7Mn0.3O3 is therefore different than that of the parent compound BiFeO3, which retains an orthorhombic structure up to its decomposition temperature. The lattice parameters of the ? phase of BiFe0.7Mn0.3O3 are pseudocubic throughout its entire stability range, despite the fact that there are still significant distortions from the cubic aristotype structure even at the onset of decomposition.