Low-Temperature Thermoelectric Properties of the Composite Crystal [Ca₂CoO_3.34]_0.614[CoO₂]

Abstract

Electric resistivity, thermoelectric power and thermal conductivity of a polycrystalline sample of the composite crystal [Ca 2 CoO 3.34 ] 0.614 [CoO 2 ], also known as Ca 3 Co 4 O 9 , 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 µV·K -1 , resistivity of ρ= 15 mΩ·cm and thermal conductivity of κ= 9.8 mW·K -1 ·cm -1 . The resulting dimensionless figure of merit becomes Z T 300 = 3.5×10 -2 , which is comparable to the value reported for a polycrystalline sample of NaCo 2 O 4 , indicating that the title compound is a potential candidate for a thermoelectric material.