Semiconductor-metal-semiconductor like transitions in amorphous Ba1-xKxBiO3-δ oxides

In this paper we report the dc conductivities of the Ba_1-xK_xBiO_3-δ (x = 0,0.2,0.4,0.625 and 0.75) glasses at different temperatures (80 to 450 K). Distinct anomalies in the temperature dependence of the dc conductivities, indicating semiconductor-metal-semiconductor (SMS) like transitions, are observed for all the glasses at temperatures ranging between 297 K and 325 K (depending on x). A similar anomaly is also observed from the dielectric constant measurements around the same temperature region. Such a SMS transition is very uncommon in oxide glasses. The orientational motion of the BiO₃ or BiO₆ structural units present in the glasses (as observed from the infrared spectra) is considered to be responsible for such anomalous behavior. A model Hamiltonian considering strong electron-phonon interaction giving rise to a lattice instability is suggested to describe such a SMS type transition observed in the present glassy systems.     

ON THE SUPERCONDUCTING MECHANISM OF K3C60 AND Ba1-xKxBiO3

A superconducting mechanism for K₃C₆₀ and Ba_1-xK_xBiO₃ has been suggested. This is the combining picture of the Cooper pair and the Ogg pair. Numerical calculations within the framework of this picture have been done for K₃C₆₀ and Ba_1-xK_xBiO₃, and the overall consistency with the experimental data of superconducting properties is good.