Temperature dependence of EXAFS spectra of BCC crystals analyzed based on classical anharmonic correlated Einstein model

Abstract

In this work, the temperature dependence of extended X-ray absorption fine structure (EXAFS) of the body-centered cubic crystals was investigated based on the anharmonic correlated Einstein model using the classical statistical theory. The oscillation of the anharmonic EXAFS spectra presented in terms of the cumulant expansion up to the fourth order. Here, the thermodynamic parameters of a system are derived from an anharmonic effective potential that has taken into account the influence of all nearest neighbors of absorbing and backscattering atoms. Analytical expressions of the first four EXAFS cumulants are obtained in simple forms of temperature or parallel mean-square relative displacement. The numerical results for crystalline molybdenum in the temperature range from 0 to 900 K are found to be in good agreement with those obtained using the other theoretical methods and experiments at various temperatures. The analytical results for the contributions of the cumulants to the amplitude reduction and phase shift of the EXAFS oscillation discover the role and meaning of high-order cumulants in analyzing the temperature dependence of the EXAFS spectra.