Pressure-induced bond buckling in YBa2Cu3O7-δ

Cu K-edge extended x-ray-absorption fine-structure (EXAFS) measurements of YBa2Cu3O7-δ ampersand hthinsp;(δ=0.05) at atmospheric pressure and at 3.4, 11.4, 31.8, and 65 kbar are presented. The experiments were performed isothermally at 80 K. In the EXAFS region, the Cu(1)-O(4)-Cu(2) path is enhanced by focused multiple scattering. Analysis indicates a buckling of this path due to out-of-line movement of the O(4) atom. The forward scattering angle β shows a rapid increase at low pressures and then saturates at 65 kbar to an angle (as large as) 12 degree depending upon the buckling model used in the EXAFS analysis. Analysis of x-ray-absorption near-edge structure data taken for the δ=0.9 and δ=0.05 compounds shows a decrease in the amplitude of the spectral feature associated with the Cu(1) atom in the δ=0.9 compound indicating that the amount of pressure-induced charge transfer from Cu(1) to Cu(2) is of the order of 0.0007 holes/kbar copyright 1999 The American Physical Society