Thermoelectric properties of NaxCo2O4 with rare-earth metals doping prepared by polymerized complex method

Abstract Polycrystalline (Na 1− y M y ) x Co 2 O 4 (M = Dy and Yb; y  = 0.01–0.05) samples were synthesized by the polymerized complex method. The effects of partial substitution of rare-earth metals for a Na-site on the thermoelectric properties of Na x Co 2 O 4 were investigated. Dy-substituted samples with y  = 0.03 and 0.05 showed the decrease in the electrical resistivity compared to the non-substituted sample because of the enhanced c -axis orientation. The power factors of the Dy-substituted samples were higher than that of the non-substituted sample over the entire temperature range investigated (400–1073 K), and the maximum power factor, 1.5 × 10 −3  W/m/K 2 , was obtained at 1073 K for the sample with y  = 0.05. The Yb-substitution caused the increase in the electrical resistivity and the Seebeck coefficient compared to the non-substituted sample over the entire temperature range, which is considered to be due to the reduction in the carrier density resulted from the Yb substitution for Na-site. The power factor of the sample with y  = 0.03 was enhanced over the entire temperature range and the maximum power factor, 1.5 × 10 −3  W/m/K 2 was obtained at 1073 K.