Doping dependence of the electronic structure of Ba1-xKxBiO3 studied by x-ray-absorption spectroscopy

We have performed x-ray-absorption spectroscopy (XAS) and x-ray-photoemission spectroscopy (XPS) studies of single crystal Ba1-xKxBiO3 (BKBO) covering the whole composition range 0 less than or equal to x less than or equal to 0.60. Several features in the oxygen 1s core XAS spectra show systematic changes with x. Spectral weight around the absorption threshold increases with hole doping and shows a finite jump between x=0.30 and 0.40, which signals the metal-insulator transition. We have compared the obtained results with band-structure calculations. Comparison with the XAS results of BaPb1-xBixO3 has revealed quite different doping dependences between BKBO and BPBO. We have also observed systematic core-level shifts in the XPS spectra as well as in the XAS threshold as functions of x, which can be attributed to a chemical potential shift accompanying the hole doping. The observed chemical potential shift is found to be slower than that predicted by the rigid band model based on the band-structure calculations. [S0163-1829(99)01023-1].