Electronic structure study of Co doped CeO2 nanoparticles using X-ray absorption fine structure spectroscopy

Abstract

We investigated the electronic structure of well characterized Co doped CeO2 nanoparticles using X-ray absorption fine structure (XAFS) spectroscopy. Near edge X-ray absorption fine structure (NEXAFS) spectra at Ce M-5,M-4, Ce L-3 and O K-edge conclude that the Ce-ions are in + 4 valence state in pure as well as in Co doped CeO2 nanoparticles. The local structure around Ce-atom in Co doped CeO2 nanoparticles was also determined using extended X-ray absorption fine structure (EXAFS) spectroscopy at Ce L-3 edge. The EXAFS analysis suggest that the inter-atomic distance of Ce-O, Ce-Ce/Co decreases with Co doping, which indicate a contraction of the lattice. The decease in Ce-O distance also reflect that there is a formation of oxygen vacancies in CeO2 matrix. The Debye-Waller factor also shows the consistent behaviour for all the coordination shells. The atomic multiplet calculations for Co L-3,L-2-edge was performed to determine the valence state, symmetry and field splitting, which reflect that Co-ions are in 2+ state and substituted at Ce-site with crystal field splitting of 10Dq = 0.57 eV. The XAFS measurements reveal that the Co-ions occupy the Ce position in the CeO2 host matrix and create a oxygen vacancy. (C) 2014 Elsevier B. V. All rights reserved.