Structural Properties of Multiferroic BiFeO3 under Hydrostatic Pressure

High-pressure structural properties of multiferroic perovskite-type BiFeO3 have been investigated by high-resolution synchrotron X-ray powder diffraction at room temperature up to 9.7 GPa. BiFeO3 shows rather complicated structural behavior. The ambient-pressure ferroelectric R3c phase transforms to an orthorhombic phase OI at around 4 GPa during compression. The OI phase is characterized by a supestructure root 2a(p) x 3 root 2a(p) x a(p), where a(p) is the parameter of the Cubic perovskite subcell (a = 5.4939(4) angstrom, b = 16.6896(9) angstrom, c = 3.8728(2) angstrom at 4.9 GPa). The OI phase transforms to an orthorhombic phase Oil at around 7 GPa. The Oil phase is characterized. by a superstructure root 2a(p) x 3 root 2a(p) x 2a(p) (a = 5.5021(3) angstrom, b = 16.2439(11) angstrom, c = 7.6960(4) angstrom at 9.7 Gila). During decompression, significant hysteretic behavior was found. The OII phase was stable down to about 3 GPa, The OII phase then transforms to an orthorhombic phase OIII that is characterized by a superstructure root 2a(p) x 2 root 2a(p) x 2a(p) (a = 5.5617(6) angstrom, b = 11.2153(10) angstrom, c = 7.7788(7) angstrom at 2.2 GPa). The R3c phase appeared below about I GPa; however, even at ambient pressure, traces of the OIII phase remained. The OIII phase seems to be isostructural with antiferroelectric PbZrO3 (space group Pbam).