Improvement on the high temperature thermoelectric performance of Ga-doped misfit-layered Ca3Co4−xGaxO9+δ (x=0, 0.05, 0.1, and 0.2)

Highly densified Ca3Co4−xGaxO9+δ (0≤x≤0.2) misfit-layered thermoelectric oxides are prepared by solid state reaction methods followed by hot-pressing. Thermoelectric properties of the samples are measured from room temperature to 1200K. The results show that partial Ga substitution leads to a simultaneous increase of the electrical conductivity and thermopower.

The Ga-doped samples have lower thermal conductivity than that of the non-doped sample in the high temperature region (>600K). The x=0.05 sample shows a higher figure of merit (Z=3.37×10−4K−1) than that of the non-doped sample (Z=1.98×10−4K−1) at 1073K, indicating significant improvement of the thermoelectric performance of Ca3Co4O9+δ by partial Ga substitution for Co.