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

Diffraction anomalous fine structure (DAFS) is the fine structure in the intensity of an X-ray diffraction peak in the vicinity of an absorption edge. DAFS is measured by monitoring the intensity of a diffraction peak as a function of the incident X-ray energy as it is scanned through an absorption edge. It combines the short range structural sensitivity of X-ray absorption spectroscopy with the long range periodicity of X-ray diffraction and can provide structural information which is not available from these techniques alone or in combination. We demonstrate the technique for several different dilute, polycrystalline samples, and present an iterative data analysis method which allows the extraction of a specific X-ray absorbance spectrum from the DAFS spectrum. We demonstrate the ability of DAFS to distinguish between the local environments in each component of a physical mixture of two phases and to separate the contributions to the X-ray absorption spectrum of the tetrahedral and octahedral cobalt sites in the spinel Co3O4. Finally, we have used DAFS to study the polarized X-ray absorption spectra from polycrystalline K2Ni(CN)4.