Separated anomalous scattering amplitudes for the inequivalent Cu sites in YBa2Cu3O7-delta using DAFS

The separate complex resonant scattering amplitudes for the two inequivalent Cu sites in YBa2Cu3O7-delta have been determined using diffraction anomalous fine structure (DAFS). The combined amplitudes Delta f(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 Delta f(Q,E) at each value of energy. For comparison, a second set of coefficients was obtained by simultaneously fitting the DAFS fine structure functions chi(Q, k) using the computer program FEFFIT under a set of constraints. The chi(Q, k) were modeled as linear combinations of the two Cu site chi(k) functions using a kinematic structure factor model with Q as the independent variable and theoretical chi(k) from FEFF7.