Preparation and high temperature thermoelectric properties of Ca3 − xAgxCo4O9 + δ oxides

Ca3 − xAgxCo4O9 + δ(x = 0, 0.01, 0.03, 0.05) oxide samples are systematically investigated with regard to their phase composition, microstructure and thermoelectric transport properties. The results show that all oxide samples are of single phase and they have layered microstructure. The polarons are stabilized by Ag doping and the carrier hopping process is influenced; the electrical resistivity and the thermopower are found to be increased simultaneously. The electrical performance is adjusted and the Ca2.97Ag0.03Co4O9 + δ sample possesses optimum power factor, the total thermal conductivity is slightly decreased and it is weakly dependent on the temperature. These results suggest that doping by heavy ions within low concentration would be an effective way improving thermoelectric performance of Ca3Co4O9 + δ system.