Preparation and Low-Temperature Thermoelectric Properties of the Composite Crystal [Ca2(Co0.65Cu0.35)2O4]0.624CoO2

A new composite crystal cobaltite, [Ca 2 (Co 0.65 Cu 0.35 ) 2 O 4 ] 0.624 CoO 2 , has been synthesized and its thermoelectric properties below 300 K have been investigated. The compound consists of a CdI 2 -type CoO 2 conduction sheet and a quadruplicated rock-salt-type [Ca 2 (Co 0.65 Cu 0.35 ) 2 O 4 ] layer alternatively stacked along the c -axis. Metallic conductivity accompanied by large thermoelectric power ( S ) has been observed down to 100 K. At 300 K, the sample exhibits S =150 µV·K -1 and resistivity of ρ=15 mΩ·cm. The resulting power factor ( S 2 /ρ) becomes 1.5×10 -4 W·K -1 ·m -2 at 300 K, which is more than 20% larger than the value reported for a polycrystalline sample of another composite crystal, [Ca 2 CoO 3 ] 0.62 CoO 2 .