BaBiO3 and the effect of potassium substitution using photoemission.

Abstract

The electronic structure and surface stability of ${\mathrm{BaBiO}}_{3}$ and ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$ are studied using photoemission. For ${\mathrm{BaBiO}}_{3}$ and ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$, 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 ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$ but show two components for ${\mathrm{BaBiO}}_{3}$, and the large shift (\ensuremath{\sim}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 ${\mathrm{BaBiO}}_{3}$ than in ${\mathrm{Ba}}_{0.6}$${\mathrm{K}}_{0.4}$${\mathrm{BiO}}_{3}$, and this may explain why such bonds are easily broken in ${\mathrm{BaBiO}}_{3}$.