Jo. Cross et al., SEPARATED ANOMALOUS SCATTERING-AMPLITUDES FOR THE INEQUIVALENT CU SITES IN YBA2CU3O7-DELTA USING DAFS, Journal de physique. IV, 7(C2), 1997, pp. 745-747
The separate complex resonant scattering amplitudes for the two inequi
valent Cu sites in YBa2Cu3O7-delta have been determined using diffract
ion anomalous fine structure (DAFS). The combined amplitudes Delta f(Q
,E) for eight specular (00l) reflections were isolated from the measur
ed intensity using the iterative dispersion algorithm of Pickering, et
al., modified to accommodate contributions to the imaginary part of t
he scattering amplitude from the heavy Ba and Y atoms. The individual
site response functions f ''(E) were solved by singular value decompos
ition 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 line
ar combinations of the two Cu site chi(k) functions using a kinematic
structure factor model with Q as the independent variable and theoreti
cal chi(k) from FEFF7.