BABIO3 AND THE EFFECT OF POTASSIUM SUBSTITUTION USING PHOTOEMISSION

The electronic structure and surface stability of BaBiO3 and Ba0.6K0.4BiO3 are studied using photoemission. For BaBiO3 and Ba0.6K0.4BiO3, bonding and nonbonding valence-band features show good agreement with theoretical calculations reported by Takegahara and Kasuya, and Mattheiss and Hamman, and Hamada et al. However, the magnitude of Bi 6s and O 2p antibonding states near the Fermi level are less than expected, and the Ba 5p core levels are at a higher energy than reported by Wertheim et al. The Bi 5d core levels show a single component for Ba0.6K0.4BiO3 but show two components for BaBiO3, and the large shift (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 et al., obtained from these materials, show that a weaker Bi-O bond exists in BaBiO3 than in Ba0.6K0.4BiO3, and this may explain why such bonds are easily broken in BaBiO3. © 1990 The American Physical Society.