Ta L3-edge XANES study of perovskite oxynitrides ATaO2N (A = Ca, Sr, Ba)

X-ray absorption near edge structure (XANES) spectroscopy was performed at the Ta L-3-edge to probe the bonding nature of tantalum and the conduction band minimum in d(0) perovskites KTaO3, CaTaO2N, SrTaO2N, and BaTaO2N. The Ta L-3 absorption edge energy (E-0) varied from 9882.2 to 9883.6 eV in the manner, KTaO3 > BaTaO2N > SrTaO2N >= CaTaO2N. These chemical shifts and the Ta-O/N bond covalency were discussed based on the bonding geometry, electronegativity of the anion, and the electronegativity of dodecahedral cation. Deconvolution of the XANES white line peak allowed for the determinations of Ta 2p -> 5d and 2p -> continuum transition energies, from which we infer that the band gap window gradually shifts to lower energy region, going from BaTaO2N to SrTaO2N to CaTaO2N. (C) 2013 Elsevier B. V. All rights reserved.