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Session Q09 - HTSC: STRUCTURES AND DEFECTS
Mixed session, Friday morning, March 24, 8:00
Ballroom A5, San Jose Convention Center
We have performed fluorescence XAFS measurements from 20-200K on a 5000 Åc-axis film of YBCO ( T_c =89K) using photons polarized perpendicular to the film. The data have high S/N out to 16 Å The data from 3-16 Åwere transformed into r -space and fit to a sum of theoretical standards out to 3.9 Å Observed trends in the fits are consistent with published diffraction results. In particular, we see no solid evidence of a split axial oxygen position. All the atom-pairs show a smooth change of their correlated broadening factors \sigma ^2 , except for features near T_c in several pairs. For instance, the Cu(1)-Ba bond shows a drop of \sim 35% in \sigma ^2 as the temperature of the sample is decreased through T_c . This feature will be related to other features present in the data and compared to results from other previously published experiments such as ion channeling. Work supported by NSF grant DMR-92-05204.