Low-temperature thermoelectric properties of the composite crystal [Ca2CoO3.34]0.614[CoO2]

Electric resistivity, thermoelectric power and thermal conductivity of a polycrystalline sample of the composite crystal [Ca2CoO3.34](0.614) [CoO2], also known as Ca3Co4O9, have been measured below 300 K. Metallic conductivity accompanied by large thermoelectric power has been observed down to 50 K. At 300 K, the sample exhibits a thermoelectric power of S = 133 mu V.K-1, resistivity of rho = 15 m Omega.cm and thermal conductivity of k = 9.8 mW.K-1.cm(-1). The resulting dimensionless figure of merit becomes ZT(300) = 3.5 X 10(-2), which is comparable to the value reported for a polycrystalline sample of NaCo2O4, indicating that the title compound is a potential candidate for a thermoelectric material.