The effect of oxygen deficiency on the electronic and local structures of BaPb1−xBixO3−δBa0.6K0.4BiO3−δ: an X-ray

The X-ray absorption spectroscopy (XAS) measurements at the Bi L3 and Pb L3 edges were made for Bi-based perovskite oxides: BaPb1−xBixO3−δ (x = 0, δ ≤ 0.2; x = 0.25, δ≤0.15; x = 1, δ ≤ 0.4) and Ba0.6BiO3−δ (δ ≤ 0.2). The oxygen reduction leads to larger changes in the Bi L3 edge of BaPb1−xBixO3−δ (x = 0.25, 1.0) and Ba0.6K0.4BiO3−δ than in the Pb L3 edge of BaPb1−xBixO3−δ (x = 0, 0.25). The extended X-ray absorption-fine structure (EXAFS) measurements indicate that the local structure around the Bi sites is more sensitive to the variation in oxygen stoichiometry than the local structure around the Pb sites. The single PbO bond length exhibits a certain dependence in BaPb1−xBixO3−δ (x = 0, 0.25) on the oxygen reduction. On the contrary, the separation between two different BiO bond lengths increases with δ in BaPb1−xBixBixO3−δ (x = 0.25, 1). Two BiO distances could be distinguished in a semiconducting Ba0.6K0.4BiO2.8. The local structure of oxygen deficient compounds was found to be essentially different from the crystalline structure refined from diffraction data. valence states are discussed. The XAS data are in agreement with a 2Bi+4 → Bi+3 + Bi+3L2 charge disproportionation model in BaPbBiO and BaKBiO, where L2 denotes the spread of two holes on 2p orbitals of six oxygen atoms surrounding the Bi ion.