Synthesis and thermoelectric properties of the new oxide ceramics Ca3−xSrxCo4O9+δ (x=0.0–1.0)

A new series of oxides Ca3−xSrxCo4O9+δ, (x=0.0–1.0) were synthesized, and their structures, electrical properties and Seebeck coefficients were measured from room temperature to 700°C. All the oxides have Ca2Co2O5 type structure. For all the oxides, both the electrical conductivity and the Seebeck coefficients increase with increasing temperature. The Seebeck coefficients are all positive. The values of Seebeck coefficient decrease with increasing Sr content for the Sr substituted samples. The power factor decreases with increasing Sr content for the samples with x<0.5, but increases for the samples with x>0.5. The Sr substituted sample (x=1.0) has lower thermal conductivity than Ca3Co4O9+δ due to its lower electrical conductivity. At 600°C, the figure of merit for Ca2SrCo4O9+δ is 0.9×10−4 K−1, and the value increases toward higher temperature.