SITE SELECTIVITY OF DAFS ANALYSIS ON HEXAFERRITE AT FE K-EDGE BY USING BOTH MONOCHROMATIC OPTICS AND ENERGY-DISPERSIVE OPTICS

DAFS (Diffraction Anomalous Fine Structure) analysis combines the chem ical and short range structural sensitivity of absorption spectroscopy and the long range structural selectivity of diffraction, so it can p rovide 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 BaZ nFe6O11 to distinguish Fe cation contributions on tetrahedral and octa hedral sites. For these experiments, diffraction intensities were meas ured as a function of the X-ray energy by scanning over the Fe K absor ption edge using both energy dispersive and classical monochromatic op tics. In the latter case, intensities of 10 Bragg reflections were col lected 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 w as performed over a continuous 250 eV energy range using dispersive fo cusing optics and a two dimensional detector. Results obtained with bo th experimental setups agree well and were analyzed using a multi-wave length refinement procedure. Since in the case of hexaferrite sample, Fe atoms in different crystallographic sites contribute to the reflect ions, intensity analyses were performed using a simultaneous refinemen t procedure of several reflections at all energies. We report the dete rmination of anomalous scattering factors f'(E), f''(E) for tetrahedra l and octahedral sites.