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Proceedings Paper

X-ray absorption fine structure of systems in the anharmonic limit
Author(s): Jose Mustre de Leon; Steven D. Conradson; I. Batistic; Alan R. Bishop; Ian D. Raistrick; W. E. Jackson; George S. Brown
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Paper Abstract

A new approach to the analysis of x-ray absorption fine structure (XAFS) data is presented. It is based on the use of radial distribution functions directly calculated from a single-particle ion hamiltonian containing model potentials. The starting point of this approach is the statistical average of the XAFS for an atomic pair. This average can be computed using a radial distribution function (RDF), which can be expressed in terms of the eigenvalues and wavefunctions associated with the model potential. The pair potential describing the ionic motion is then expressed in terms of parameters that are determined by fitting this statistical average to the experimental XAFS spectrum. This approach allows the use of XAFS as a tool for mapping near-neighbor interatomic potentials, and allows the treatment of systems which exhibit strongly anharmonic potentials which can not be treated by perturbative methods. Using this method we have analyzed the high temperature behavior of the oxygen contributions to the Fe K-edge XAFS in the ferrosilicate minerals andradite (Ca3Fe2Si3O12) and magnesiowustite (Mg0.9Fe0.1O). Using a temperature dependent anharmonic correction derived from these model compounds, we have found evidence for a local structural change in the Fe-O coordination environment upon melting of the geologically important mineral fayalite (Fe2SiO4). We have also employed this method to the study of the axial oxygen contributions to the polarized Cu K-edge XAFS on orientated samples of YBa2Cu3O7 and related compounds. From this study we find evidence for an axial oxygen-centered lattice distortion accompanying the superconducting phase transition and a correlation between this distortion and Tc. The relation of the observed lattice distortion to mechanisms of superconductivity is discussed.

Paper Details

Date Published: 1 November 1991
PDF: 12 pages
Proc. SPIE 1550, X Rays in Materials Analysis II: Novel Applications and Recent Developments, (1 November 1991); doi: 10.1117/12.49470
Show Author Affiliations
Jose Mustre de Leon, Los Alamos National Lab. (United States)
Steven D. Conradson, Los Alamos National Lab. (United States)
I. Batistic, Los Alamos National Lab. (United States)
Alan R. Bishop, Los Alamos National Lab. (United States)
Ian D. Raistrick, Los Alamos National Lab. (United States)
W. E. Jackson, Stanford Univ. (United States)
George S. Brown, Stanford Univ. (United States)


Published in SPIE Proceedings Vol. 1550:
X Rays in Materials Analysis II: Novel Applications and Recent Developments
Dennis M. Mills, Editor(s)

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