X-ray absorption fine structure of systems in the anharmonic limit

Jose Mustre de Leon; Steven D. Conradson; I. Batistic; Alan R. Bishop; Ian D. Raistrick; W. E. Jackson; George S. Brown

doi:10.1117/12.49470

1 November 1991 X-ray absorption fine structure of systems in the anharmonic limit

Jose Mustre de Leon, Steven D. Conradson, I. Batistic, Alan R. Bishop, Ian D. Raistrick, W. E. Jackson, George S. Brown

Proceedings Volume 1550, X Rays in Materials Analysis II: Novel Applications and Recent Developments; (1991) https://doi.org/10.1117/12.49470
Event: San Diego, '91, 1991, San Diego, CA, United States

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.

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Jose Mustre de Leon, Steven D. Conradson, I. Batistic, Alan R. Bishop, Ian D. Raistrick, W. E. Jackson, and George S. Brown "X-ray absorption fine structure of systems in the anharmonic limit", Proc. SPIE 1550, X Rays in Materials Analysis II: Novel Applications and Recent Developments, (1 November 1991); https://doi.org/10.1117/12.49470

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KEYWORDS

Copper

Oxygen

Chemical species

Iron

Superconductors

Materials analysis

Ions

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