On Monday 24 August 2009 04:21:01 pm Dr Somaditya Sen wrote:

I am having problems in comparing the real bond length as obtained from EXAFS data and Reitveld analysis of XRD data of te same sample. The bond lengths as observed from the XAFS data seems to be much smaller that that from XRD. Is there some multiplication factor known in literature to address this issue?

As Jason said, you seem to be neglecting the scattering phase shift in the EXAFS equation, which has the effect of shifting a peak in the Fourier transform by about 0.3 - 0.5 angstroms to a lower value. This is taken into account correctly by the data analysis software such that results reported from a fit represent a measurement of an actual interatomic difference. There is a broader question, though. Should you expect Reitveld and XAS to give the same answer for your sample? Reitveld measures long-range correlations while XAS is an inherently local probe. If there is some kind of local disorder in your material, then it may not be reasonable to expect the two to agree. Indeed, the manner in which they disagree is often the very purpose of doing the XAS experiment. Your question is pretty fundamental. There is a lot of material available at http://xafs.org to help you get started understanding your XAS measurements. I think you would benefit by poking around there. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/