J. Phys. IV France 7 (1997) C2-745-C2-747
Separated Anomalous Scattering Amplitudes for the Inequivalent Cu Sites in YBa2Cu3O7-δ using DAFSJ.O. Cross1, M. Newville2, L.B. Sorensen3, H.J. Stragier3, C.E. Bouldin4 and J.C. Woicik4
1 Naval Research Laboratory, Washington DC 20375, U.S.A.
2 Lawrence Livermore National Laboratory, Livermore CA 94550, U.S.A.
3 Department of Physics, Box 351560, University of Washington, Seattle, WA 98195, U.S.A.
4 National Institute of Standards and Technology, Gaithersburg, Maryland, U.S.A.
The separate complex resonant scattering amplitudes for the two inequivalent Cu sites in YBa2Cu3O7-δ have been determined using diffraction anomalous fine structure (DAFS). The combined amplitudes Δf(Q,E) for eight specular (00l) reflections were isolated from the measured intensity using the iterative dispersion algorithm of Pickering, et al., modified to accommodate contributions to the imaginary part of the scattering amplitude from the heavy Ba and Y atoms. The individual site response functions f''(E) were solved by singular value decomposition of the matrix of crystallographic coefficients and applying the inverse matrix to Δf(Q,E) at each value of energy. For comparison, a second set of coefficients was obtained by simultaneously fitting the DAFS fine structure functions X(Q,E) using the computer program FEFFIT under a set of constraints. The X(Q,E) were modeled as linear combinations of the two Cu site X(Q,E) functions using a kinematic structure factor model with Q as the independent variable and theoretical X(Q) from FEFF7.
© EDP Sciences 1997