Differences of structural and electronic properties in Ba1-xKxBiO3 (x=0, 0.04, and 0.4)

Electronic structures calculated based upon the extended Huckel tight-bindi ng method for Ba1-xKxBiO3 with x = 0, 0.04, and 0.4 are reported. It is not iced that the commensurate ordering of Bi3+ and Bi5+ is responsible for the insulating and semiconducting behavior in BaBiO3 and Ba0.96K0.04BiO4. The band gaps of 3.2 eV and 1.4 eV for the former and the latter compounds, res pectively, are consistent with the experimental results. Doping in Bi 6s-bl ock band up to x = 0.4 causes the collapse of the ordering of Bi3+ and Bi5, thereby resulting in the superconductivity in the Ba0.6K0.4BiO3 compound. Strikingly, the character of oxygen contributes to the conducting mechanis m than that of the bismuth. This is quite different from the cuprate superc onductors in which the character of copper dominates that of oxygen.