Diffraction anomalous fine structure measurements by using an energy/angular ‘‘dispersive diffraction’’ experimental setup

Abstract

DAFS (diffraction anomalous fine structure) measurements give intensity variations of x-ray Bragg reflections as the energy is tuned near an absorption edge of an atom of the sample. In this way, the long-range structural information contained in the diffraction peak is combined with the chemical and local structure selectivity of x-ray absorption spectroscopy. Generally, for such experiments diffraction intensities are measured using classical monochromatic optics. In this report, we propose a new energy/angular ‘‘dispersive diffraction’’ setup which allows a parallel intensity collection over the whole energy range. This method was demonstrated on a hexaferrite single crystal where intensity variations of eight Bragg reflections have been measured at the Fe K edge over a spectral range of 250 eV. The same DAFS measurements were performed using double-crystal optics and we compare both results. This experiment was done on a sample where, for all reflections, contributions of different Fe sites are mixed. An intensity analysis of these reflections, which was performed by a simultaneous refinement procedure of several reflections at all energies, is also given.