Probing the local atomic structure in CoLa<inf>0.15</inf>Fe<inf>1.85</inf>O<inf>4</inf> as a function of the synthesis method by multi edge XAFS

Abstract

We combined x-ray powder diffraction (XRD) and x-ray absorption fine structure spectroscopy (XAFS) to characterize the crystallographic and local atomic structure of nanosized La3+ substituted CoFe2O4 spinel ferrite of composition CoLa0.15Fe1.85O4 synthesized by different synthesis routes: standard ceramic technique, citric acid (citrate) precursor and urea assisted flash auto-combustion process. Rietveld refinement of XRD patterns allowed to describe the long-range atomic structure that was used as structural model for quantitative analysis of XAFS spectra collected at the Fe-K, Co-K and La-L3 and refined via a multi-edge approach, which provided details about local atomic structure and coordination chemistry around the absorbers. Combining the complementary information from XRD and XAFS it was possible to reliably describe the cation distribution over the two spinel sublattices (tetrahedral and octahedral) as a function of the synthesis routes. We demonstrated that the inversion parameter, the cation distribution, and the local atomic structure depend strongly on the synthesis method which in particular affects the La3+ lattice-site and vacancies. In particular the citrate synthesis appears to provide a pure single pure phase with highest coordination number of La and lowest inversion parameter.