Improvement on the High temperature Thermoelectric Performance of Ga-doped Misfit-layered Ca3Co4-xGaxO9+ (x = 0, 0.05, 0.1, and 0.2)

Highly densified Ca3Co4−xGaxO9+ı (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 1200 K. 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 (> 600 K). The x = 0.05 sample shows a higher figure of merit (Z = 3.37×10−4 K−1) than that of the non-doped sample (Z = 1.98×10−4 K−1) at 1073 K, indicating significant improvement of the thermoelectric performance of Ca3Co4O9+ı by partial Ga substitution for Co.
Keyword: Thermoelectricity; Misfit cobalt oxides; Figure of merit; Hot press