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Author Booth, C. H. ♦ Bridges, F. ♦ Boyce, J. B. ♦ Claeson, T. ♦ Lairson, B. M. ♦ Liang, R. ♦ Bonn, D. A.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword MATERIALS SCIENCE ♦ PHYSICS ♦ HIGH-TC SUPERCONDUCTORS ♦ BOND LENGTHS ♦ YTTERBIUM OXIDES ♦ BARIUM OXIDES ♦ COPPER OXIDES ♦ QUATERNARY COMPOUNDS ♦ MONOCRYSTALS ♦ FILMS ♦ X-RAY SPECTRA ♦ ABSORPTION SPECTRA ♦ FINE STRUCTURE ♦ TEMPERATURE RANGE 0013-0065 K ♦ TEMPERATURE RANGE 0065-0273 K
Abstract We have performed fluorescence x-ray-absorption fine-structure (XAFS) measurements from 20{endash}200 K on a 5000-A {ital c}-axis film of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} (YBCO) on MgO ({ital T}{sub {ital c}}=89 K) using photons polarized perpendicular to the film. The quality of the data is high out to 16 A{sup {minus}1}. The data from 3{endash}15.5 A{sup {minus}1} were transformed into {ital r} space and fit to a sum of theoretical standards out to 4.0 A. These data are compared to YBCO data from a single crystal and from a film on LaAlO{sub 3} with the same {ital T}{sub {ital c}}. The main difference between the single crystal and the film data is that while the single-crystal data are well described by a two-site axial oxygen [O(4)] distribution, we see no evidence for such a distribution in either thin-film sample. We place an upper limit on the size of the axial oxygen distribution splitting for the film on MgO at {Delta}{sub {ital r}}{approx_lt}0.09 A. Therefore, the magnitude of any possible splitting is not directly related to {ital T}{sub {ital c}}. Fits to the temperature-dependent data from the YBCO film on MgO indicate that all bonds show a smooth change of their broadening factor {sigma}, except the Cu-O(4) bonds, which show an increase in {sigma} in the vicinity of {ital T}{sub {ital c}}, followed by a decrease of the same magnitude. Such a feature does not occur in diffraction measurements. Since XAFS measurements of {sigma} include any correlation between the atoms in a given bond, we conclude that the O(4) position becomes less correlated with the Cu positions near {ital T}{sub {ital c}}. Correlation measurements of these and several further near neighbors are also reported. {copyright} {ital 1996 The American Physical Society.}
ISSN 01631829
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-10-01
Publisher Place United States
Journal Physical Review, B: Condensed Matter
Volume Number 54
Issue Number 13


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