EXAFS Debye-Waller factor and thermal vibrations of crystals.

The EXAFS Debye-Waller factor depends on the correlation of atomic motion and can yield original information on the vibrational dynamics of crystalline solids. In this paper an introductory treatment of thermal disorder in EXAFS, based on thc cumulant approach, is given. Thc general relation between mean-square relative displacement (MSRD) measured by EXAFS and atomic thermal vibrations in harmonic approximation is explored. Strengths and limitations of the phenomenological Einstein- and Debye-correlated models are discussed. Some of the most significant results so far obtained are reviewed. A relatively simple method for estimating anharmonic corrections to the MSRD is proposed.