Crystal structure of the monoclinic and cubic polymorphs of BiMn{sub 7}O{sub 12}

Journal Article · Fri Jan 15 00:00:00 EST 2010 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.10.013· OSTI ID:21372466

Okamoto, H ^[1]; Imamura, N ^[2]; Karppinen, M; Yamauchi, H ^[2]; Fjellvag, H ^[1]

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1. Centre for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, P.O. Box 1033 Blindern, NO-0315 Oslo (Norway)
2. Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan)

The complex perovskite BiMn{sub 7}O{sub 12} occurs with two polymorphic structures, cubic and monoclinic. Currently their crystal structures are investigated with high-resolution synchrotron powder X-ray diffraction at room temperature. Rietveld analysis reveals unusual behavior for, respectively, the oxygen and bismuth atoms in the monoclinic and cubic phases. Bond valence calculations indicate that all the Mn atoms in both the phases are in trivalent state. Possible roles of the 6s{sup 2} lone-pair electrons of Bi{sup 3+} in BiMn{sub 7}O{sub 12} are discussed in comparison with the LaMn{sub 7}O{sub 12} phase that is isomorphic to monoclinic BiMn{sub 7}O{sub 12}. Multiple roles of the lone-pair electrons are revealed, causing (i) A-site cation deficiency, (ii) octahedral tilting, (iii) A-site cation displacement, and (iv) Mn{sup 3+} Jahn-Teller (JT) distortion. Relationships between the monoclinic and cubic phases are discussed with emphasis on the MnO{sub 2} and MnO{sub 6} local structural aspects. All Mn atoms in the monoclinic polymorph have distorted coordination consistent with JT-active Mn(III) high spin, whereas for the cubic polymorph, the B-site Mn atoms show regular octahedral coordination. - Graphical abstract: The complex perovskite BiMn{sub 7}O{sub 12} occurs with polymorphic structures, cubic and monoclinic. Structural analysis reveals unusual behavior for oxygen and bismuth in the monoclinic and cubic phases, respectively. Unusually large (and anisiotropic) displacement parameters for some of the oxygen ions in the monoclinic phase indicated competition between non-equivalent Mn-O bonds for the corner-sharing d-type JT Mn{sub B}O{sub 6} and square-planar Mn{sub A''}O{sub 4} polyhedra.

• OSTI ID: 21372466
• Journal Information: Journal of Solid State Chemistry, Vol. 183, Issue 1; Other Information: DOI: 10.1016/j.jssc.2009.10.013; PII: S0022-4596(09)00497-6; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BISMUTH COMPOUNDS
BISMUTH IONS
CUBIC LATTICES
JAHN-TELLER EFFECT
MANGANESE IONS
MANGANESE OXIDES
MONOCLINIC LATTICES
PEROVSKITE
TEMPERATURE RANGE 0273-0400 K
X-RAY DIFFRACTION
CHALCOGENIDES
CHARGED PARTICLES
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIFFRACTION
IONS
MANGANESE COMPOUNDS
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PEROVSKITES
SCATTERING
TEMPERATURE RANGE
TRANSITION ELEMENT COMPOUNDS