Thermoelectric properties of lower concentration K-doped Ca3Co4O9 ceramics

The tuning of electron and phonon by ion doping is an effective method of improving the performances of thermoelectric materials. A series of lower concentration K-doped Ca3-xKxCo4O9 (x = 0, 0.05, 0.10, 0.15) polycrystalline ceramic samples are prepared by combining citrate acid sol-gel method with cold-pressing sintering method. The single-phase compositions and plate-like grain morphologies of all samples are confirmed by x-ray diffraction and field emission scanning electron microscope. The effects of lower concentration K doping on the thermoelectric properties of the material are evaluated systematically at high temperatures (300-1026 K). Low concentration K doping causes electrical conductivity to increase up to 23% with little effect on the Seebeck coefficient. Simultaneously, the thermal conductivity of K-doped sample is lower than that of the undoped sample, and the total thermal conductivity reaches a minimum value of approximately 1.30 W.m(-1).K-1 , which may be suppressed mainly by the phonon thermal conduction confinement. The dimensionless figure-of-merit ZT of Ca2.95K0.05CO4O9 is close to 0.22 at 1026 K, representing an improvement of about 36% compared with that of Ca3Co4O9 , suggesting that lower concentration K-doped Ca3Co4O9 series materials are promising thermoelectric oxides for high-temperature applications.