Thermoelectric properties of Bi2.3-xPbxSr2.6Co2Oy single crystals

A set of single crystals of the layered cobaltite Bi2.3-xPbxSr2.6Co2Oy (0 l ess than or equal to x less than or equal to 0.44) were prepared by a flux technique. The resistivity rho and the thermopower S along the in-plane dir ection were measured, and the thermoelectric properties were compared with those of other oxides. The Pb substitution causes a decrease in rho and an increase in S below 100 K, which improves the power factor S-2/rho by 3-4 t imes. The transport parameters exhibit an anomaly near 25-50 K, such as a p lateau in S and an upturn in rho, which we ascribe to the reduction of the density of states owing to a pseudogap.