DIFFRACTION ANOMALOUS FINE-STRUCTURE - A NEW TECHNIQUE FOR PROBING LOCAL ATOMIC ENVIRONMENT

Diffraction anomalous fine structure (DAFS) is the fine structure in t he intensity of an X-ray diffraction peak in the vicinity of an absorp tion edge. DAFS is measured by monitoring the intensity of a diffracti on peak as a function of the incident X-ray energy as it is scanned th rough an absorption edge. It combines the short range structural sensi tivity of X-ray absorption spectroscopy with the long range periodicit y of X-ray diffraction and can provide structural information which is not available from these techniques alone or in combination. We demon strate the technique for several different dilute, polycrystalline sam ples, and present an iterative data analysis method which allows the e xtraction of a specific X-ray absorbance spectrum from the DAFS spectr um. We demonstrate the ability of DAFS to distinguish between the loca l environments in each component of a physical mixture of two phases a nd to separate the contributions to the X-ray absorption spectrum of t he tetrahedral and octahedral cobalt sites in the spinel Co3O4. Finall y, we have used DAFS to study the polarized X-ray absorption spectra f rom polycrystalline K2Ni(CN)4.