J. Phys. IV France 7 (1997) C2-137-C2-140
XAFS and Thermal AveragingE.A. Stern
Department of Physics, Box 351560, University of Washington, Seattle, WA 98195, U.S.A.
XAFS measures ρ(r), the distribution of the magnitude r of the relative vector displacement f between a center probe atom and its neighbors. The related ρ(r→) of the distribution of the vector distance between the probe atom and its neighbors defines a pair potential V(r→) which is thermally averaged over the position of all of the other atoms in the material being investigated. It is shown that there are subtle differences between ρ(r) and p(r→) which lead to a new correction term to XAFS measurements necessary to obtain the correct thermal expansion of interatomic distances. Besides measuring ρ(r), XAFS allows the determination of both ρ(r→) and V(r→) which include σ2⊥ addition to the usual σ2x, the mean squared vibrational disorder perpendicular and along the line between the average position of the pair of atoms, respectively.
© EDP Sciences 1997