Enhancement of high temperature thermoelectric performance in Bi, Fe co-doped layered oxide-based material Ca3Co4O9+δ

Polycrystalline Ca3−xBixCo4−yFeyO9+δ (x = 0, y = 0; x = 0.3, y = 0; x = 0.3, y = 0.1) samples have been prepared by solid state reaction followed by spark plasma sintering process. The thermoelectric properties have been systematically investigated from room temperature to near 1000 K. It is found that Bi substitution leads up to 40% reduction in the thermal conductivity, which is mainly associated with doping-induced point defect phonon scattering. In addition, the power factor was found to be increased by ∼33% by the co-doping of Fe and Bi. In present study, the thermoelectric figure of merit achieves ∼0.4 at 973 K by the co-doped sample Ca2.7Bi0.3Co3.9Fe0.1O9+δ. It indicates that the combined effects of such a co-doping approach can effectively improve the thermoelectric performance of Ca3Co4O9+δ-based material.