Thermoelectric properties of Pb doped ＄[Ca_{2}CoO_{3.1}]_{0.62}CoO_{2}＄

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We have prepared polysrystalline specimens of ＄[(Ca_{1-x}Pb_{x})_{2}CoO_{3.1}]_{0.62}CoO_{2}＄ using a conventional solid-state reaction method, and investgated the Pb substitution effect on the TE properities. 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 ＄[Ca_{2}CoO_{3}]＄ block layer. The valence state of Co ions in the ＄CdI_2＄ type ＄[CoO_{2}]＄ 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 polycrystalline sample of ＄Naco_{2}O_{4}＄.
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