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

In this study, a new synthesis route for the Ca3Co4O9 compound using a CoIICoIII-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 Co3O4 as a precursor by the CoIICoIII-Layered Double Hydroxide leads to the formation of a single Ca3Co4O9 phase. The thermoelectric properties of the Ca3Co4O9 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 CoIICoIII-Layered Double Hydroxide as precursor rather than Co3O4, 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.