title: Spectroscopic observation of bipolaronic point defects in Ba(1-x)KxBiO3.
abstract: An infrared-absorption band centered at 0.85 eV, which is below the big optical absorption at the charge-density-wave (CDW) gap energy of 1.85 eV, has been observed for semiconducting single crystalline Ba(1-x)KxBiO3. With substituting K for Ba, the spectral weight of the new band increases with x, while that of the CDW-gap excitation decreases. Since the impurity state with the K substitution is known to be nonmagnetic at low temperatures, Bi3+ the state with 6s2 electrons surrounded by the six Bi5+ ions forms a small bipolaron by losing a pair of electrons in the Rice-Sneddon model. The new band is assigned to a transition from the lower-Peierls band to a state of the bipolaronic point defect.
authors.affiliation: Institute of Materials Science, University of Tsukuba, Tennoudai, Tsukuba, Ibaraki, 305-8573, Japan.
authors.forename: Taichiro
authors.initials: T
authors.lastname: Nishio
authors.forename: Javed
authors.initials: J
authors.lastname: Ahmad
authors.forename: Hiromoto
authors.initials: H
authors.lastname: Uwe