X-ray absorption study of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ and Gd/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7/ superconductors

X-ray absorption measurements of the high-T/sub c/ superconductors Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-δ/ and Gd/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-δ/ are essentially identical and show no significant difference in either near-edge or local structure from 4.2K to 688K. The position of the Cu edge suggests that the Cu valence in the superconductors is between that in CuO (formal valence of II) and that in KCuO/sub 2/ (formal valence of III). The authors' EXAFS structural results agree well with the diffraction data. From the atomic vibrations, the authors find that the 2D Cu-O planes and the 1D Cu-O chains form the most rigid parts of the structure, with an Einstein temperature of about 560K, compared with 390K for the Y-O bonds, 320K for Ba-O, and 260K for Cu-Cu and Y-Cu