Antipolar phase in multiferroic BiFeO_3 at high pressure

摘要

The crystal and magnetic structures of BiFeO_3 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) A. The variation of the structural parameters of both phases as a function of pressure was determined. The initially incommensurate G-type antiferromagnetic structure of BiFeO_3 becomes commensurate due to the structural phase transition.