Lattice dynamics of manganites RMnO3 (R = Sm, Eu or Gd): Instabilities and coexistence of orthorhombic and hexagonal phases

Abstract

The lattice dynamical and allied properties of the multiferroic manganites SmMnO3, EuMnO3 and GdMnO3 were investigated in this work by means of a shell model with transferable pairwise interionic interaction potential. This shell-model potential is able to reproduce the available crystal structure and phonon frequencies. A zone center imaginary Au mode is observed in these lattice dynamics calculations that indicates metastability of the perovskite phase. Comparison of the Gibbs free energies in the orthorhombic and hexagonal phases points to the possible coexistence of the two phases of these manganites under ambient conditions. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.