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Contribution of powder diffraction for structure refinements of aperiodic misfit cobalt oxides
Author(s) -
Grebille Dominique,
Lambert Sébastien,
Bourée Françoise,
Petříček Václav
Publication year - 2004
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889804018096
Subject(s) - crystallography , superspace , aperiodic graph , powder diffraction , triclinic crystal system , crystal structure , superstructure , neutron diffraction , cobalt , diffraction , chemistry , synchrotron , materials science , physics , inorganic chemistry , mathematics , optics , thermodynamics , combinatorics , supersymmetry , mathematical physics
Two families of misfit cobalt oxides have been reinvestigated using neutron and synchrotron powder diffraction data and Rietveld structure refinements in the four‐dimensional formalism for aperiodic structures. In the first system [Ca 2 CoO 3 ][CoO 2 ] 1.62 , the structure‐specific features of two complex polytypic phases previously described from single‐crystal diffraction data have been confirmed for the main term of the series and are described with the C 2/ m (1,δ,0) s 0 superspace symmetry ( R p = 0.026, R wp = 0.031, R B = 0.014). The high‐resolution synchrotron diffraction experiments have been interpreted with a triclinic distortion of the structure, probably related to an intrinsic modulation of the [Ca 2 CoO 3 ] sublattice in relation with Co and O split atomic sites. In the second system Ca 0.82 (Cu 0.65 Co 0.35 O 2 ), a new occupation modulation of the metallic site is shown with the Fmmm (α11)0 ss superspace symmetry ( R p = 0.031, R wp = 0.039, R B = 0.027) and is interpreted in relation with the modulated interatomic distances of the square coordination of the cationic site. In both cases, recently developed tools for structure refinements of aperiodic systems using powder diffraction data (in the JANA2000 package) have proved their efficiency, in particular as specific complements to previous single‐crystal structure refinements.