Structural instabilities in Aurivillius compound Bi4Mn3O12 from First Principles

TINTE, SILVIA; STACHIOTTI, MARCELO; WEHT, RUBEN

Encuentro; American Physical Society, APS March Meeting 2010, March 15-19,2010; 2010

Layered perovskite oxide materials are good candidates for the potential synthesis of natural multiferroic materials. One approach is to choose a ferroelectric host and to incorporate a magnetically active species. The Aurivillius layered perovskites are chosen because most are ferroelectric. Described by the formula [Bi2O2][An-1BnO3n+1], they are formed by stacking Bi2O2 slabs with n perovkitelike blocks. A ferroelectric prototype compound is Bi4Ti3O12 (BIT), where bismuth also occupies the A sites. Using first-principles calculations, we investigate here the three-layer Aurivillius Bi4Mn3O12 (BIM) that results of substituting all Ti^4+ B-site cations in the BIT lattice by Mn^4+ cations. We report the structural instabilities in the high-symmetry tetragonal structure (space group symmetry I4/mmm). We find an unstable Eu phonon mode, which mainly involves movements of the Bi ions in the perovskite A sites with respect to the TiO6 octahedra. This instability, also observed in non-magnetic BIT and associated to the in-plane electronic polarization, suggests the presence of ferroelectricity in BIM. We also explore different collinear spin orderings of the magnetic Mn atoms and its effect on the structural instabilities.