Extended x-ray absorption fine structure analysis of interatomic distances, coordination numbers, and mean relative displacements in disordered alloys

A procedure is described for determining interatomic distances $r$, coordination numbers $N$, and mean relative displacements $\sigma$ from extended x-ray absorption fine structure (EXAFS) data on disordered metallic systems. This procedure includes the case when the spectrometer has finite energy resolution. It is shown how the absolute value of the EXAFS can be determined. A way has been developed to determine the inelastic loss factors of the photoelectrons from model compounds of known structure. The procedure has been checked on four metallic systems (Cu, $\alpha -\mathrm{Al}\mathrm{Cu}$-AlCu, ${\theta }^{\prime }$ and $\theta$ AlCu). The accuracy of the analysis is 1% for the interatomic distances, 15% for the coordination numbers, and 20% for $\sigma$. The reliability of the data analysis, which depends strongly on the number of different atoms in a shell, on the magnitude of their mean relative displacement and on the difference in their backscattering power will be discussed at length.