Peculiar High-Pressure Behavior of BiMnO3

High-pressure structural properties of perovskite-type BiMnO3 have been investigated by synchrotron X-ray powder diffraction at room temperature. A new monoclinic phase having P2(1)/c symmetry was found between about 1.5 and 5.5 GPa. Above 8 GPa, the orthorhombic GdFeO3-type phase (space group Pnma) is stable. The crystal structure of BiMnO3 at 8.6 GPa and room temperature was investigated (a=5.5132(3) angstrom, b=7.5752(3) angstrom, c=5.4535(3) angstrom). The orthorhombic phase of BiMnO3 has an orbital order similar to LaMnO3 but with a different arrangement of orbitals in the ac plane. High-pressure room-temperature behavior of BiMnO3 differs from high-temperature behavior at ambient pressure in comparison with BiCrO3 and BiScO3. These findings may open new directions in investigation of BiMnO3.