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+delta (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 x 10(-4) K-1) than that of the non-doped sample (Z = 1.98 x 10(-4) K-1) at 1073 K, indicating significant improvement of the thermoelectric performance Of Ca3Co4O9+delta by partial Ga substitution for Co. (C) 2009 Elsevier B.V. All rights reserved.