Sintering Temperature Dependence of Thermoelectric Performance and Crystal Phase of Calcium Cobalt Oxides

Abstract

Polycrystalline samples were synthesized by a conventional solid‐state reaction. As starting materials, Co 3 O 4 and Ca(OH) 2 were mixed in a molar ratio of Ca:Co=3:4 and sintered at 1073–1373 K. The compound phases and thermoelectric properties of the resulting products were dependent on the sintering temperature. X‐ray diffraction analysis showed that the Ca 3 Co 4 O 9 compound was stable up to 1193 K and that Ca 3 Co 2 O 6 was formed at 1273 K. At 1373 K, the sample decomposed into cobalt oxide and calcium oxide. A maximum power factor of about 100 μW/(K 2 ·m) at 873 K was obtained for the Ca 3 Co 4 O 9 phase sintered at 1193 K.