Soft X-ray absorption spectroscopy study of (Ba0.5Sr0.5) (Co0.8Fe0.2)(1-x)NbxO3-delta with different content of Nb (5%-20%)

摘要

The mixed electronic ionic conducting materials (Ba0.5Sr0.5) (Co0.8Fe0.2)(1-x)NbxO3-delta with partial Nb substitution (x: 0.05, 0.10, 0.15, 0.20) for B cations (Co/Fe), synthesized using a solid state reaction method, have been studied by near edge X-ray absorption fine structure (NEXAFS). Co L-2,L-3- absorption spectra of (Ba0.5Sr0.5) (Co0.8Fe0.2)(1-x)NbxO3-delta (BSCFN) powders were analyzed with the purpose to understand the influence of the Nb substitution on the atomic electronic structure of BSCFN. The joint analysis of the Co L-2,3(-) absorption spectra reveals the presence of mixed oxidation states Co2+/Co3+ in all the studied BSCFN structures. It was established that the proportion of oxidation states Co2+/Co3+ and the corresponding coordinations of Co atoms depend on the content of Nb. In the 10% Nb substituted BSCF sample Co atoms mostly occur in the Co2+ oxidation state and are preferentially characterized by an octahedral coordination site. In all other structures Co atoms are rather characterized by Co2+/Co3+ oxidation states and occupy both octahedrally and tetrahedrally coordinated sites. (C) 2015 Elsevier B.V. All rights reserved.