Normal-state transport properties of Ba1-xKxBiO3 crystals

The normal-state transport properties of Ba1-xKxBiO3 crystals with a wide range of potassium compositions (0 less than or equal to x less than or equal to 0.62) were studied. Although the host material BaBiO3 has a monoclinic structure, the system changes from a monoclinic to an orthorhombic structure with a small doping of potassium (0 less than or equal to x 0.35) and behaves similar to a doped semiconductor, without exhibiting superconductivity. In the composition range, holes are majority carriers in the transport phenomena. When x exceeds a critical value (similar to 0.35), the system goes into a cubic superconducting phase with a single metallic band. The vicinity of the critical composition transport phenomena is easy to understand assuming the existence of two conducting channels that are made up of metallic and semiconducting phases. Maximum T-c exceeding 30 K was observed at x similar to 0.4, where carrier density was at its maximum. Overdoping with potassium suppresses superconductivity. In the metallic composition of x > 0.45, transport seems to correlate with the phonon mode with an energy distribution of 15-43 meV. (C) 1999 Elsevier Science Ltd. All rights reserved.