Thermoelectric Properties of Bi- and Na-substituted calcium cobaltite textured by TGG method

Abstract

We prepared plate-like particles of Bi- and Na-substituted Ca₃Co₄O₉ and fabricated dense and highly textured ceramics of (Ca_2.70Na_0.15Bi_0.15)Co₄O₉ by combining the templated grain growth technique (TGG) with hot-pressing (HP). The alignment of grains with developed ab-plane enhanced electrical conductivity of the dense and highly textured TGG+HP specimen when compared with the specimen sintered under uniaxial pressure (UP+PLS). The improved electrical conductivity with high Seebeck coefficient of the highly oriented specimen (TGG+HP) gave a high thermoelectric power factor of 5.9×10^-4 W/mK² at 1073 K. The figures-of-merit at 773 K and 1073 K were calculated to be 8.54×10^-5 K^-1 (ZT=0.066 at 773 K) and 1.69×10^-4 K^-1 (ZT=0.18 at 1073 K), respectively.