Structure change of Mn2O3 under high pressure and pressure-induced transition

Abstract

Abstract Bixbyite (Mn,Fe)2O3 has a C-type rare-earth oxide structure with space group of Ia-3 and different from corundum structure R-3c. Single-crystal structure analyses and powder diffraction experiments were carried out using synchrotron radiation under high pressures up to 41.21 GPa. Lattice constants and bond distances were elucidated as a function of pressure. Single crystal structure analyses under high pressures up to 9.64 GPa have been executed using DAC. There are two octahedral Mn3+ sites: M1 (-3) and M2 (-2.). M1O6 and M2O6 octahedral volumes and void space of vacant sites show different compression curves. M1O6 octahedron is less compressive than M2O6 octahedron. The former is a little deformed from an ideal octahedron with m-3m of MnO6 but the latter is a largely distorted octahedron. The quadratic elongation is applied in order to comprehend the polyhedral distortion and finite homogeneous strain. Both octahedra do not show a noticeable Jahn-Teller distortion induced from Mn3+. Six bond lengths of M1O6 are equivalent but the octahedron more elongates along the direction of -3 axis with increasing pressure and is more deformed from the regular octahedron. The M2O6 octahedron has two long bond distances among six bonds, which are most compressive. The octahedral deformations seem to reduce the Jahn-Teller effect due to the compression. The bulk modulus: Ko = 169.1(4.9) GPa and Ko′ = 7.35(0.99), was observed from the volume change with pressure. Pressure-induced phase transition was confirmed at about 21 GPa with a large hysteresis. The transition is reversible and non-quenchable. Powder indexing of the high-pressure phase was carried out using diffraction pattern taken at 35.06 GPa. It has a monoclinic symmetry and is not a corundum, Rh2O3(II) or perovskite structure.