Synthesis and properties of oxygen non-stoichiometric BiMnO3

Abstract

We have investigated oxygen non-stoichiometric BiMnO_3±δ 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 BiMnO_3−δ. It was confirmed that stoichiometric BiMnO₃ adopts the monoclinic phase I structure (space groupC2/c) in agreement with previous reports, and BiMnO₃ is a ferromagnet with T_C = 100 K. Single-phase BiMnO_3.04, BiMnO_3.08, and BiMnO_3.12 samples were prepared with the monoclinic phase II structure and ferromagnetic transitions at T_C = 85, 80, and 72 K, respectively. However, in the case of BiMnO_3.08 and BiMnO_3.12, very weak reflections breaking the symmetry of the C-centered monoclinic cell were observed. BiMnO_3.16 crystallizes in an orthorhombic system with lattice parameters (a = 5.5143(1) Å, b = 7.8106(2) Å, and c = 5.5614(1) Å in space groupPnma) close to those of LaMnO_3.11. BiMnO_3.16 shows a spin-glass transition at 30 K.