Site selectivity of DAFS analysis on hexaferrite at Fe K edge by using both monochromatic optics and energy dispersive optics

Abstract

DAFS (Diffraction Anomalous Fine Structure) analysis combines the chemical and short range structural sensitivity of absorption spectroscopy and the long range structural selectivity of diffraction, so it can provide site selective spectroscopy information or chemically sensitive structural one. We have undertaken our experiment in the vicinity of the Fe K absorption edge on a single crystal of Y-type hexaferrite BaZnFe6O11 to distinguish Fe cation contributions on tetrahedral and octahedral sites. For these experiments, diffraction intensities were measured as a function of the X-ray energy by scanning over the Fe K absorption edge using both energy dispersive and classical monochromatic optics. In the latter case, intensities of 10 Bragg reflections were collected at about one hundred discrete photon energies with a step width of a few eV over a spectral range of 800 eV. We also report the first DAFS measurements obtained by energy/angular “dispersive diffraction”. During these “energy/angular dispersive diffraction” experiments, a simultaneous collection of the same Bragg reflection intensities was performed over a continuous 250 eV energy range using dispersive focusing optics and a two dimensional detector. Results obtained with both experimental setups agree well and were analyzed using a multi-wavelength refinement procedure. Since in the case of hexaferrite sample, Fe atoms in different crystallographic sites contribute to the reflections, intensity analyses were performed using a simultaneous refinement procedure of several reflections at all energies. We report the determination of anomalous scattering factors f′(E), f″(E) for tetrahedral and octahedral sites.