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

Abstract

We report the results of a high-resolution powder neutron-diffraction study of multiferroic BiFe${}_{0.7}$Mn${}_{0.3}$O${}_{3}$. We have confirmed the previous assignment of the $\ensuremath{\alpha}$ phase and $\ensuremath{\beta}$ phase as having $R3c$ and $Pbnm$ symmetry, respectively. The $\ensuremath{\gamma}$ 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 $R\overline{3}c$. The $\ensuremath{\gamma}$ phase of BiFe${}_{0.7}$Mn${}_{0.3}$O${}_{3}$ is therefore different than that of the parent compound BiFeO${}_{3}$, which retains an orthorhombic structure up to its decomposition temperature. The lattice parameters of the $\ensuremath{\gamma}$ phase of BiFe${}_{0.7}$Mn${}_{0.3}$O${}_{3}$ 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.