Distance dependence of mean-square relative displacements in EXAFS

We have investigated the sensitivity of extended x-ray-absorption fine structure (EXAFS) to the local atomic dynamics beyond the first shell in several elements (Ge, Cu, Ni) and binary compounds (ZnS and GaSb) at low temperature (12 K and 80 K). Debye-Waller factors were extracted up to the tenth shell in some cases allowing for a comprehensive experimental investigation of the distance dependence of the mean-square relative displacement. We demonstrate that the observed distance dependencies cannot be satisfactorily described by commonly used theoretical models. The origins of these discrepancies and the importance of long-range EXAFS information are discussed.