Valence states of bismuth in new mixed-valence oxides: Bi1−xYxO1.5+δ (x = 0.4) by XANES

Bi1−xYxO1.5+δ (x ∼ 0.4, 0 < δ < 0.16) is a recently identified bismuth mixed-valence oxide. To provide clear evidence of the valence state of the Bi ion, Bi L3 X-ray absorption near edge structure (XANES) spectra were measured in polycrystalline materials. These spectra were found to be similar to that of Bi2O3 as a reference to B3+. An observed systematic decrease centered on ∼13427 eV associated with the increase of δ was clarified by subtracting the spectrum of δ = 0 from that of δ = δ. The spectrum of δ = 0.5, which was calculated using both δ = 0 and δ = 0.16, was similar to that of NaBiO3. As δ increased, the position of the inflection point of the main peak at about 13448 eV, assigned to a 2p-6d transition, shifted toward higher energy. This indicated the oxidation of Bi ions in Bi0.6Y0.4O1.5+δ.