Antipolar phase in multiferroic BiFeO3 at high pressure

The crystal and magnetic structures of BiFeO3 have been studied at high pressures up to 8.6 GPa by means of neutron powder diffraction at ambient temperature. Upon compression, a reduction of the spontaneous ferroelectric polarization is evidenced from the analysis of atomic displacements in the rhombohedral phase. A structural phase transition from the polar rhombohedral R3c phase to the antipolar orthorhombic Pbam phase with antiferroelectic character of atomic displacements was revealed at P = 3 GPa. The lattice parameters of the Pbam phase at P = 4.1 GPa are a = 5.5177(4), b = 11.159(1) and c = 7.7550(6) angstrom. The variation of the structural parameters of both phases as a function of pressure was determined. The initially incommensurate G-type antiferromagnetic structure of BiFeO3 becomes commensurate due to the structural phase transition.