Pressure induced phase transitions in multiferroic BiFeO3

Using synchrotron based angle dispersive x-ray diffraction measurements and first principles calculations we have studied the high pressure behavior of pervoskite BiFeO3. We report two structural phase transitions under pressure viz., at ∼4.1 and ∼6.4 GPa. Our first principles calculations, combined with Rietveld refinement of the diffraction data, suggest that both the high pressure phases are orthorhombic, the first being P2221 and the second phase belonging to the space group Pnma. These results are in contrast to the previous studies such as the observation of monoclinic phase below 10 GPa. Theoretical structural optimization in the present case indicates the utility of incorporating the chemical bonding in Rietveld refinement of complex structures.