Peculiar high-pressure behavior of BiMnO3.

High-pressure structural properties of perovskite-type BiMnO(3) 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 GdFeO(3)-type phase (space group Pnma) is stable. The crystal structure of BiMnO(3) at 8.6 GPa and room temperature was investigated (a = 5.5132(3) A, b = 7.5752(3) A, c = 5.4535(3) A). The orthorhombic phase of BiMnO(3) has an orbital order similar to LaMnO(3) but with a different arrangement of orbitals in the ac plane. High-pressure room-temperature behavior of BiMnO(3) differs from high-temperature behavior at ambient pressure in comparison with BiCrO(3) and BiScO(3). These findings may open new directions in investigation of BiMnO(3).