Comparative study of EXAFS spectra for close-shell systems

Many systems of real interest for Extended X Ray Absorption Fine Spectroscopy have closed coordination shells. In this paper we focus on the local structural characteristics of supported nickel catalysts and Fe 3 0 4 core-shell nanocomposites. The latter are obtained by the polymerization of a conducting polypyrrole shell around Fe 3 O 4 nanoparticles. The local structure of Fe and Ni atoms were determined through Extended X-ray Absorption Fine Structure analysis based on the comparative study of the radial distribution function calculated with the classical fast Fourier transform and the Filon quadrature. The radial distribution function can be efficiently calculated by the fast Fourier transform when the coordination shells are well separated while the Filon quadrature gives remarkable results for close-shell coordination. The present work achieved an adequate comparison between different Fourier transform methods for obtaining very accurate local structure results.