Highly-dense and textured Ca3Co4O9 ceramic samples were obtained by a spark plasma sintering (SPS) process. The sintering conditions were modified to optimize the degree of orientation and the bulk densities which are important for their thermoelectric performance. Their thermoelectric properties were measured from room temperature to 1,180 K in air. The maximum power factor was achieved at 1,153 K in the SPS-sintered case because of the maximum electrical conductivity owing to both the degree of orientation and bulk density. In order to improve the thermoelectric performance of this SPS-sintered Ca3Co4O9 system a doping effect with various dopants was also investigated. Ca3Co4O9 samples doped with Ag, Bi, and Na were prepared. Three factors including acceptor doping, a grain boundary phase and elevated mobility caused enhanced electrical conductivities. And these increased electrical conductivities resulted in increased power factors.

Keywords: Thermoelectric oxides, Texture structure, Ca3Co4O9, Spark plasma sintering.