Topological short-range disorder in Au1−xNix solid solutions: An extended x-ray-absorption fine-structure spectroscopy and computer-simulation study

Abstract

The present extended x-ray-absorption fine-structure (EXAFS) investigation aims at determining the atom-pair displacements on a local scale in the ${\mathrm{Au}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Ni}}_{\mathrm{x}}$ system, for the three types of pairs Au-Au, Au-Ni, and Ni-Ni. X-ray-absorption spectra have been obtained above both edges (Au $L_3$ and Ni K), over the whole composition range. For the purpose of the separation of the Au and Ni scattering contributions, a detailed analysis of EXAFS over a wide photoelectron wave-vector range beginning close to the edge has been performed. The amplitude and phase functions for unlike-neighbor pairs have been obtained in two ways: first by using empirically refined theoretical partial phase shifts, which enabled us to calculate the total phase functions, and secondly by making use of fluorescence recorded spectra of dilute alloys from which appropriate amplitude functions have been extracted. Many low-k amplitude effects such as the photoelectron wave curvature, the experimental energy resolution, the limited core-hole lifetime, and the many-electron excitation factors have been analyzed, and taken into account, as well as the difference between p- and d-symmetry photoelectron scattering.