Ta L₃-edge XANES study of perovskite oxynitrides ATaO ₂N (A = Ca, Sr, Ba)

X-ray absorption near edge structure (XANES) spectroscopy was performed at the Ta L₃-edge to probe the bonding nature of tantalum and the conduction band minimum in d⁰ perovskites KTaO₃, CaTaO₂N, SrTaO₂N, and BaTaO₂N. The Ta L ₃ absorption edge energy (E₀) varied from 9882.2 to 9883.6 eV in the manner, KTaO₃ > BaTaO₂N > SrTaO ₂N ≥ 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.