Electrical and thermal properties of the Ca 3-x Gd x Co 4O 9+δ system

The effects of Gd substitution on the thermoelectric (TE) properties of Ca3Co4O9+delta have been systematically investigated from 25 K to 335 K. Partial substitution of Gd in Ca3Co4O9+delta results in an increase of thermopower and resistivity, and a decrease of thermal conductivity. A maximum dimensionless figure of merit (ZT) of 0.028 was achieved at 335 K for Ca2.4Gd0.6Co4O9+delta , which is about one order of magnitude larger than that for Ca3Co4O9+delta . The investigation demonstrates that the TE performance of the Ca3Co4O9+delta system can be improved through Gd doping.