High temperature transport and thermoelectric properties of Ag-substituted Ca3Co4O9+δ system

Polycrystalline Ca3−xAgxCo4O9+δ (0 ≤ x ≤ 0.3) samples were prepared by solid-state reaction method and the thermoelectric properties were studied from 300 up to 1000 K. With the substitution of Ag+ for Ca2+, the resistivity decreased while thermoelectric power increased simultaneously, and the thermal conductivity was found to decrease monotonically with increasing Ag content. These results indicated that the thermoelectric performance of the Ca3Co4O9+δ system could be optimized remarkably with the substitution of Ag. The power factor would reach 700 μW m−1 K−2 and the figure of merit ZT could exceed 0.3 at 1000 K for the x = 0.3 sample, suggesting a promising thermoelectric oxide candidate at high temperatures.