Enhancement of metallic behavior in bismuth cobaltates through lead doping- art. no. 094109

Single crystals of Bi2M3Co2Oy phases with M = Ca, Sr, and Ba were synthesiz ed by the flux method. The undoped Ca and Sr analogs are semiconducting whi le the Ba analog has a metal to semiconductor transition at approximate to 80 K. Pb-substituted single crystals in which Pb partially substitutes for Bi were prepared by a similar method. Transmission electron microscopy carr ied out on single crystals of the undoped phases reveals a super-structure similar to that of superconducting bismuth-2212. This superstructure disapp ears when the Sr and Ba compounds are Pb doped. Transport measurements show that Pb doping induces a clear increase in the metallic character of the s amples for Sr and Ba analogs. The metal to semiconductor transition in Bi2B a3Co2Oy is suppressed by Pb doping, and (Bi, Pb)(2)Ba3Co2Oy is metallic dow n to 30 mK. The magnetic-susceptibility data do not show any evidence of or dering, and the magnetic moment Co atom was found to be approximate to 1 mu (B). Resistivity measurements carried out up to 20 GPa show that the sampl es become more semiconducting with increasing pressure.