Synthesis and properties of oxygen non-stoichiometric BiMnO3

We have investigated oxygen non-stoichiometric BiMnO3 +/-delta samples. It was found that the oxygen deficient samples could not be prepared by the direct high-pressure high-temperature method and other methods should be developed for the preparation of BiMnO3-delta. It was confirmed that stoichiometric BiMnO3 adopts the monoclinic phase I structure (space group C2/c) in agreement with previous reports, and BiMnO3 is a ferromagnet with T-C 100 K. Single-phase BiMnO3.04, BiMnO3.08, and BiMnO3.12 samples were prepared with the monoclinic phase II structure and ferromagnetic transitions at TC 85, 80, and 72 K, respectively. However, in the case of BiMnO3.08 and BiMnO3.12, very weak reflections breaking the symmetry of the C-centered monoclinic cell were observed. BiMnO3.16 crystallizes in an orthorhombic system with lattice parameters (a = 5.5143(1) angstrom, b = 7.8106(2) angstrom, and c = 5.5614(1) angstrom in space group Pnma) close to those of LaMnO3.11. BiMnO3.16 shows a spin-glass transition at 30 K.