Abstract
The extended X-ray absorption fine structure (EXAFS) has been developed into a powerful technique and is widely applied to determine many structural parameters and dynamic properties of materials. The EXAFS technique is now the technique of choice in many materials science investigations, and the EXAFS data analysis is being performed in many laboratories spread around the world. In this work, the anharmonic EXAFS spectra of crystalline nickel (Ni) has been analyzed based on the quantum anharmonic correlated Einstein model. The anharmonic EXAFS oscillation presented in terms of the Debye-Waller factors using the cumulant expansion approach up to the fourth-order. This calculation model has been developed from the high-order anharmonic effective potential that described the contribution of their nearest-neighbor atoms to the pair interaction potential. The analytical expressions of the anharmonic EXAFS cumulants are not only explicit forms but also satisfy all of their fundamental properties in temperature dependence. The analysis of the anharmonic EXAFS spectra was performed by evaluating the contributions of the cumulants to the amplitude reduction and the phase shift of the anharmonic EXAFS oscillation. The numerical results for Ni were in good agreement with those obtained using the other theoretical methods and experiment at various temperatures, which are useful for analyzing the experimental EXAFS data of the metal crystals.
Highlights
The structural parameters and dynamic properties of materials can be determined from the extended X-ray absorption fine structure (EXAFS) technique [1,2,3,4,5]
The EXAFS analysis is performed based on evaluating the contribution of the DW factors to the amplitude reduction and phase shift in the cumulant expansion approach up to fourth-order
These analytical results show the role of the high-order EXAFS cumulants in the anharmonic EXAFS oscillation
Summary
The structural parameters and dynamic properties of materials can be determined from the extended X-ray absorption fine structure (EXAFS) technique [1,2,3,4,5]. The connection between the Debye-Waller (DW) factors and the EXAFS cumulants was described in detail in the cumulant expansion approach (ratio method) by Bunker (1983) [7] and exploited by Tranquada & Ingalls (1983) [11]. The position of atoms is not stationary, and their interatomic distance always changes due to thermal vibrations [4,5,6] that were detected by Beni & Platzman (1976) [2] and Eisenberger & Brown (1979) [3] They cause anharmonic effects on crystal vibrations and smear out the EXAFS oscillations [3, 6].
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