Study of the Cu-Au and Ag-Au Alloy Systems as a Function of Composition and Order through the Use of the Mössbauer Effect forAu197

Mössbauer spectra for ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ and the alloy electrical resistivities have been measured for ordered and disordered phases of Cu-Au and Ag-Au alloys. The alloy compositions span the complete range (∼ 0-100)% Au. The change of isomer shift with pressure between ∼ 0 and 65 kbar has also been measured for ordered ${\mathrm{Cu}}_3$Au. A theoretical model is given which describes the isomer shift in terms of the average atomic volume of the alloy, the short-range-order parameters, and the alloy composition. The agreement between the model and our measurements is good. Friedel oscillations are shown to be present in the electron charge distribution in these alloys. An estimate of the relative contributions of alloy-volume and short-range-order effects to the average electron charge density at the gold nuclei is given.