Determination of dopant site occupancies in Cu-substituted YBa2Cu3O7−δ by differential anomalous x-ray scattering

Abstract

Dopant site occupancies in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_{3\mathrm{-}\mathrm{x}}$ ${\mathrm{M}}_{\mathrm{x}}$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, with M=Fe (x=0.3 and x=0.5), Co (x=0.2 and x=0.5), Ni (x=0.3), and Zn (x=0.3) have been found using differential anomalous x-ray scattering. The Ni and Zn atoms were found to occupy the Cu(1) (‘‘chains’’) site and the Cu(2) (‘‘planes’’) site in a nearly random distribution. The Fe and Co atoms were found to occupy the Cu(1) site predominantly at low x, with an increasing fraction on the Cu(2) sites as the total amount of dopant increases. In all cases, our results appear to have high statistical significance, with very little sensitivity to expected uncertainties in oxygen content, total dopant content, anomalous corrections to the atomic scattering factor of the dopant, and to relative atomic coordinates assumed in the modeling. We have also discussed the results in the context of existing extended x-ray-absorption fine-structure and neutron-diffraction results, thermogravimetric analysis, and Mössbauer spectra, and $T_c$ and Hall-effect studies.