•M. Merz1, M. Meven1, N. Nücker2,
S. Schuppler2, S. Ustinovich3, A. Soldatov3,
S. Shiryaev3, S. Barilo3, D. Arena4, J.
Dvorak4, S. Stadler4 und Y. Idzerda4
1Institut für Kristallographie, RWTH-Aachen
2Forschungszentrum Karlsruhe, IFP, Karlsruhe
3Academy of Sciences, Minsk
4Naval Research Laboratory, Washington
With O 1s near-edge x-ray absorption spectroscopy, the unoccupied electronic structure of Ba1-xKxBiO3 and (Ba,K)3Bi2O7 single crystals as well as of highly-ordered Ba1-xKxBiO3 films has been investigated using the surface-insensitive fluorescence yield. Clear indications for both, a charge-density wave derived band as well as a conduction band are found. The data support a picture, where the intrinsically doped holes in BaBiO3 predominantly reside on the oxygen orbitals of the compressed BiV+-O octahedra, leading to the well-known static charge disproportionation and the alternation of enlarged and compressed octahedra. Upon substitution of Ba by K, the intensity attributed to the unoccupied states resulting from the charge-density wave is effectively reduced. Concomitantly, the spectral weight of the conduction band develops and shows a marked increase with growing K content. For higher potassium concentrations (x ³ 0.5), on the other hand, a small amount of holes still remains in the O 2p states of the charge-density wave, thereby pointing to a local, and most probably dynamical, breathing mode of the BiO6 octahedra.