Electron correlation effect in the thermoelectric oxide Ca3−xSrxCo4O9single crystals

We have measured the transport properties of the thermoelectric layered oxide Ca3−xSrxCo4O9 () single crystals to examine the electron correlation effect. Both the electrical resistivity and the Seebeck coefficient systematically vary with increasing Sr content x. In all the present crystals, the resistivity shows a Fermi-liquid behavior of ρ = ρ0 + AT2 at around 120 K, and A increases with increasing Sr content, indicating that the effective mass is enhanced by the substitution. It is also found that the low-temperature Seebeck coefficient increases with increasing Sr content. These results suggest that the present isovalent Sr substitution acts as a negative pressure on this compound and that the two dimensionality is thus enhanced by the substitution, leading to a strong renormalization of the effective mass. We also discuss the Sr-substitution effect on the carrier concentration.