Pressure-induced bond buckling in YBa2Cu3O7-δ

Cu K-edge extended x-ray-absorption fine-structure (EXAFS) measurements of YBa₂Cu₃O_7-δ (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° 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