Effect of high pressure on multiferroic BiFeO3

We report experimental evidence for pressure instabilities in the model multiferroic BiFeO₃ and, namely, reveal two structural phase transitions around 3.5 and 10 GPa by using diffraction and far-infrared spectroscopy at a synchrotron source. The intermediate phase crystallizes in a monoclinic space group, with octahedra tilts and small cation displacements. When the pressure is increased further the cation displacements (and thus the polar character) of BiFeO₃ is suppressed above 10 GPa. The nonpolar orthorhombic Pnma structure observed above 10 GPa is in agreement with recent theoretical ab initio prediction, while the intermediate monoclinic phase has not been predicted theoretically.