Thermoelectric properties of Gd, Y co-doped Ca3Co4O9+δ

The Ca3−x−yGdxYyCo4O9+δ precursor powders were synthesized by the polyacrylamide gel method. The powders were sintered by the spark plasma sintering (SPS). The DTA analysis showed that the synthesis temperature of Ca3Co4O9+δ was about 933 K, which is lower than that of the conventional citric acid method. The resistivities, the Seebeck coefficients and the thermal conductivities of the samples were measured from room temperature to 973 K. The Seebeck coefficients and the resistivities of the doped samples were remarkably enhanced due to the decrease of the carrier concentration, whereas the thermal conductivities of them were decreased due to the impurity scattering effect. The maximal ZT value of 0.26 was obtained at 973 K for Ca2.7 Gd0.15 Y0.15Co4O9+δ.