Single-crystalline BiMnO3 studied by temperature-dependent x-ray diffraction and Raman spectroscopy

We report on the temperature dependence of the phonons and crystallographic parameters in BiMnO3 single
crystals grown under high pressure and high temperature. The crystallographic structure of the sample was refined
from room temperature to liquid helium temperature in the centrosymmetric C2/c space group, i.e., a group
which does not allow ferroelectricity. In addition, the lattice dynamics was probed by Raman spectroscopy down
to liquid nitrogen temperature, i.e., below the ferromagnetic transition at TC = 100 ± 2 K. Both crystallographic
and Raman data indicate the absence of a structural phase transition at the ferromagnetic ordering or any other
temperature. The Raman signature around TC shows a significant spin-phonon coupling for the high-frequency
bands.