X-Ray Absorption Study of Y1Ba2Cu3O7 and Gd1Ba2Cu3O7 Superconductors

X-ray absorption measurements of the high-Tc superconductors Y1Ba2Cu3O7-δ and Gd1Ba2Cu3O7-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 KCuO2 (formal valence of III). Our EXAFS structural results agree well with the diffraction data. From the atomic vibrations, we find that the 2D Cu-O planes and the ID 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.