Distortions in the local structure of HgBa _2 CuO _4 from XAFS spectra at the Cu and Ba K-edges, and Hg L3-edge.

Session Q09 - HTSC: STRUCTURES AND DEFECTS
Mixed session, Friday morning, March 24, 8:00
Ballroom A5, San Jose Convention Center

[Q09.04] Distortions in the local structure of HgBa _2 CuO _4 from XAFS spectra at the Cu and Ba K-edges, and Hg L3-edge.

Frank Bridges,Corwin H. Booth,Eric Bauer (University of California, Santa Cruz),Tord Claeson (Chalmers University of Technology),C. W. Chu (University of Houston)

We report XAFS results taken at the Cu and Ba K-edges, and the Hg L3-edge for a high- T_c (96 K) and a lower- T_c (45 K) sample of HgBa _2 CuO _4 (Hg1201). The XAFS spectra look very similar for the two samples at each of the edges. Fits to the Hg L3-edge spectra indicate that the near neighbor oxygens are well ordered with respect to the mercury. However, the fit to the Hg-Hg/Hg-Ba peak suggests some distortion of the Hg/Ba environment. Fits to the Ba K-edge data indicate that number of neighbors and average bond lengths agree well with published diffraction studies; however, the Ba-O(2) (axial oxygen) peak is severely broadened, much more so than expected from the diffraction results. The Cu K-edge results are similar to the Ba K-edge fits in that the Cu-O(2) is also very broad. Possible correlated distortions will be discussed and compared with previously proposed distortions obtained from diffraction studies. Work supported by NSF grant DMR-92-05204.

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