Extended x-ray absorption fine structure determination of thermal disorder in Cu: Comparison of theory and experiment

The extended x-ray absorption fine structure (EXAFS) of Cu at temperatures from 10 to 683K has been used to evaluate the EXAFS disorder term and compare it with theory. The change in disorder for different temperatures was extracted from the slopes of $\ln \left(\frac{{\chi }_1}{{\chi }_2}\right)$ plots and by using a least-squares curve-fitting program. The values of the disorder parameter vs temperature are compared to a pure Debye model without correlation, a Debye model with correlation, and a model incorporating the measured phonon spectrum of Cu. The pure Debye model predicts too large an effect, whereas there is good agreement between the experimental data and either of the other two theories. This indicates that models which account for the correlated motion of the absorbing and scattering atom can give $\sigma$ values which are in good agreement with those determined experimentally.