title: Origin of the monoclinic-to-monoclinic phase transition and evidence for the centrosymmetric crystal structure of BiMnO3.
abstract: Structural properties of polycrystalline single-phased BiMnO3 samples prepared at 6 GPa and 1383 K have been studied by selected area electron diffraction (SAED), convergent beam electron diffraction (CBED), and the Rietveld method using neutron diffraction data measured at 300 and 550 K. The SAED and CBED data showed that BiMnO3 crystallizes in the centrosymmetric space group C2/c at 300 K. The crystallographic data are a = 9.5415(2) A, b = 5.61263(8) A, c = 9.8632(2) A, beta = 110.6584(12) degrees at 300 K and a = 9.5866(3) A, b = 5.59903(15) A, c = 9.7427(3) A, beta = 108.601(2) degrees at 550 K, Z = 8, space group C2/c. The analysis of Mn-O bond lengths suggested that the orbital order present in BiMnO3 at 300 K melts above TOO = 474 K. The phase transition at 474 K is of the first order and accompanied by a jump of magnetization and small changes of the effective magnetic moment and Weiss temperature, mueff = 4.69 microB and theta = 138.0 K at 300-450 K and mueff = 4.79 microB and theta = 132.6 K at 480-600 K.
authors.affiliation: Advanced Nano Materials Laboratory (ANML) and High Voltage Electron Microscopy Station (HVEMS), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Alexei A
authors.initials: AA
authors.lastname: Belik
authors.forename: Satoshi
authors.initials: S
authors.lastname: Iikubo
authors.forename: Tadahiro
authors.initials: T
authors.lastname: Yokosawa
authors.forename: Katsuaki
authors.initials: K
authors.lastname: Kodama
authors.forename: Naoki
authors.initials: N
authors.lastname: Igawa
authors.forename: Shinichi
authors.initials: S
authors.lastname: Shamoto
authors.forename: Masaki
authors.initials: M
authors.lastname: Azuma
authors.forename: Mikio
authors.initials: M
authors.lastname: Takano
authors.forename: Koji
authors.initials: K
authors.lastname: Kimoto
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Matsui
authors.forename: Eiji
authors.initials: E
authors.lastname: Takayama-Muromachi