Local structure of disordered Au-Cu and Au-Ag alloys

Abstract

X-ray-absorption fine structure (XAFS) and x-ray-diffraction (XRD) measurements of disordered alloys ${\mathrm{Au}}_{x}{\mathrm{Cu}}_{1\ensuremath{-}x}$ and ${\mathrm{Au}}_{0.5}{\mathrm{Ag}}_{0.5}$ prepared by melt spinning were performed. In the ${\mathrm{Au}}_{0.5}{\mathrm{Ag}}_{0.5}$ alloy, no significant local deviations of the atoms from the average fcc lattice were detected while in ${\mathrm{Au}}_{x}{\mathrm{Cu}}_{1\ensuremath{-}x}$ alloys, significant deviations of atoms from the average fcc lattice were found. Mean-square vibrations of the Cu-Cu distances revealed by the XAFS in ${\mathrm{Au}}_{x}{\mathrm{Cu}}_{1\ensuremath{-}x}$ alloys indicate the weakening of contact between Cu atoms in the dilute limit. Our computer simulation for ${\mathrm{Au}}_{x}{\mathrm{Cu}}_{1\ensuremath{-}x}$ clusters of ${10}^{5}$ atoms reproduces the main features of both the XAFS and XRD data.