Thermoelectric properties of Pb doped [Ca2CoO3.1]0.62CoO2

We have prepared polycrystalline specimens of [Ca₂CoO _3.1]_0.62CoO₂ (0 les x les 0.03) using the conventional solid-state reaction method, and investigated the Pb substitution effect on the TE properties. With the Pb substitution, both the electrical resistivity and Seebeck coefficient do not change drastically. This is attributed to the carrier concentration. Seebeck and Hall coefficient measurements reveal that the major charge carriers in the samples are holes, however, the carrier concentration does not change drastically with increasing x. The magnetic susceptibility measurements also show that Pb ions take divalent state in the rock salt type [Ca₂CoO₃] block layer. The valence state of Co ions in the CdI₂ type [CoO₂] sheet was 3.1+ and that of Co ions in the block layer was 3.6+. The dimensionless figure of merit for the x = 0 sample at room temperature was 0.02, which is approximately equal to the corresponding values of a polycrystalline sample of NaCo₂O₄