PHOTOEMISSION AND X-RAY-ABSORPTION STUDY OF SUPERCONDUCTING AND SEMICONDUCTING BA1-XKXBIO3 SINGLE-CRYSTALS

Semiconducting Ba0.9K0.1BiO3 and superconducting Ba0.6K0.4BiO3 single crystals cleaved in situ have been studied by core level and valence b and photoelectron spectroscopy and O K edge x-ray absorption spectrosc opy. It was found that the general shape of the valence band spectrum agrees with the shape predicted by band structure calculations, but th e intensity near the Fermi level, was lower in the experimental spectr um as compared to the calculated. The O K edge spectra showed that the metallic phase is not related to the presence of doping inducted O 2p holes. This property of Ba1-xKxBiO3 shows that the semiconductor-meta l transition of this system is of a different nature than that of the hole doped cuprate high-T-c superconductors. The core level photoemiss ion spectra of the cations showed a small asymmetry for Ba0.9K0.1BiO3. Corresponding spectra for Ba0.6K0.4BiO3 showed a larger asymmetry res ulting in a resolved high binding energy shoulder in the Bi 4f spectru m. The origin of this feature is discussed.