BaBiO3 and the effect of potassium substitution using photoemission

The electronic structure and surface stability of BaBiO{sub 3} and Ba{sub 0.6}K{sub 0.4}BiO{sub 3} are studied using photoemission. For BaBiO{sub 3} and Ba{sub 0.6}K{sub 0.4}BiO{sub 3}, bonding and nonbonding valence-band features show good agreement with theoretical calculations reported by Takegahara and Kasuya, and Mattheiss and Hamman, and Hamada {ital et} {ital al}. However, the magnitude of Bi 6{ital s} and O 2{ital p} antibonding states near the Fermi level are less than expected, and the Ba 5{ital p} core levels are at a higher energy than reported by Wertheim {ital et al}. The Bi 5{ital d} core levels show a single component for Ba{sub 0.6}K{sub 0.4}BiO{sub 3} but show two components for BaBiO{sub 3}, and the large shift ({similar to}1.6 eV) of the second component to lower binding energy suggests the possible reduction of surface Bi to the metallic state. Examination of extended x-ray-absorption fine-structure data by Heald {ital et al}., obtained from these materials, show that a weaker Bi-O bond exists in BaBiO{sub 3} than in Ba{sub 0.6}K{sub 0.4}BiO{sub 3}, and this may explain why such bonds are easily broken in BaBiO{sub 3}.