Synthesis of thermoelectric Ca3Co4O9 ceramics with high ZT values from a CoIICoIII-Layered Double Hydroxide precursor

Abstract In this study, a new synthesis route for the Ca 3 Co 4 O 9 compound using a Co II Co III -Layered Double Hydroxide compound as a precursor has been demonstrated. Polycrystalline samples have been prepared by solid state reaction and sintered by spark plasma sintering. XRD study shows that the substitution of Co 3 O 4 as a precursor by the Co II Co III -Layered Double Hydroxide leads to the formation of a single Ca 3 Co 4 O 9 phase. The thermoelectric properties of the Ca 3 Co 4 O 9 samples at high temperature have been studied (550–1100 K). The nature of the precursor does not significantly affect the Seebeck coefficient, the electrical conductivity and the power factor. However, the thermal conductivity is decreased when using the Co II Co III -Layered Double Hydroxide as precursor rather than Co 3 O 4 , 1.6 W m −1 K −1 compared to 2.1 W m −1 K −1 at 1073 K respectively. This leads to a 20% ZT improvement at 1000 K, 0.18 compared to 0.15 respectively.