Thermodynamic Properties of Bcc Crystals Studied Based on Their High-Order Expanded Debye-Waller Factors and XAFS Application to Ferrite Iron

Abstract

Thermodynamic properties of bcc crystals have been studied based on the anharmonic correlated Debye model high-order expanded Debye-Waller factors and X-ray absorption fine structure (XAFS). The many-body effects are taken into account in the present one-dimensional model based on the anharmonic effective potential that includes interactions of absorber and backscatterer atoms with their first shell near neighbors, where Morse potential is assumed to describe the single-pair atomic interaction. Analytical expressions for dispersion relation, correlated Debye frequency and temperature and four first temperature-dependent XAFS cumulants of bcc crystals have been derived using the many-body perturbation approach. The obtained cumulants are applied to calculating XAFS spectra and their Fourier transform magnitude. Numerical results for Fe, a ferrite crystal, are found to be in good agreement with experiment.