The use of the correlated Debye model for EXAFS-based thermometry in bcc and fcc metals

Abstract: Extended X-ray absorption fine structure (EXAFS) spectra are sensitive to thermal disorder and are often used to probe local lattice dynamics. Variations in interatomic distances induced by atomic vibrations are described by the temperature-dependent mean-square relative displacement (MSRD), also known as the Debye-Waller factor. In this study, we evaluated the feasibility of addressing the inverse problem, i.e., determining the sample temperature from the analysis of its EXAFS spectrum using the multiple-scattering formalism, considering contributions up to the 4th-7th coordination shell. The method was tested on several monatomic metals (bcc Cr, Mo, and W; fcc Cu and Ag), where the correlated Debye model of lattice dynamics provides a fairly accurate description of thermal disorder effects up to distant coordination shells. We found that the accuracy of the method strongly depends on the temperature range. The method fails at low temperatures, where quantum effects dominate and MSRD values change only slightly. However, it becomes more accurate at higher temperatures, where the MSRD shows a near-linear dependence on temperature.