Effect of hydrogen annealing of ball-milled Bi0.5Sb1.5Te3 powders on thermoelectric properties

The combination technique of ball-milling and sintering is commonly employed to manufacture high performance thermoelectric materials. However, during ball-milling and sintering, it is hard to avoid inclusion of oxygen in the lattice, which results in degradation of the thermoelectric properties. In this study, hydrogen annealing was carried out at different temperatures to remove the dissolved oxygen. The reduced oxygen content was confirmed after hydrogen annealing, and the extent of the reduction was increased with annealing temperature. The carrier (holes) concentration was increased with the reduction of the oxygen content, which is attributed to the increased concentration of the antisite defects. Consequently, the electrical conductivity was considerably increased whereas the Seebeck coefficient was marginally decreased. The variation of the Seebeck coefficient was interpreted with complex electronic structure. As a result, the power factor and ZT were enhanced 27.0% and 18.2%, respectively, compared with the non-annealed sample.