Structure of feromagnetic BiMnO3 synthesized at high pressure has been determined by electron diffraction and neutron powder diffraction. This structure is related to a heavily distorted perovskite structure, having monoclinic symmetry, space group C2, with a = 9.5323(6) Å, b = 5.6064(3) Å, C = 9.8535(7) Å, and β = 110.667(5)°. The distortion is caused by a polarized Bi 6s2 lone pair. Every trivalent manganese cation reveals the Jahn-Teller distortion and ordering of a vacant dx2-y2 orbital is suggested to play an important role for the ferromagnetism.
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