Annealing effect on thermoelectric properties of TiCoSb half-Heusler compound

The half-Heusler compound TiCoSb was prepared by arc melting. We annealed the ingot for 1, 3, and 7 days at 1173 K, and measured the electrical resistivity, thermoelectric power, and thermal diffusivity in the temperature region from 350 to 973 K. We found that the dimensionless figure of merit ZT decreased with increasing annealing period. We have considered that the changes of thermoelectric properties are derived from two competitive phenomena; the first one is the introduction of structural disorder due to evaporation of impurity antimony, and the second one is the improvement of the disorder effect by annealing.