Effect of oxygen content on thermoelectric properties of n-type (Bi,Sb)2(Te,Se)3 alloys prepared by rapid solidification and hot-pressing techniques

Influence of oxygen content on the microstructure and thermoelectric properties of bismuth-telluride based (Bi,Sb)(2)(Te,Se)(3) alloys has been investigated. The consolidated specimens in a disc form of 10 and 26 min in diameter and 8 min in height were prepared by hot-pressing of rapidly solidified foils produced by a single-roller melt spinning method. Oxygen content was analyzed to be enriched in the range of 4.1 nm depth from the foil or powder surface. By the reduction-treatment process in a hydrogen atmosphere, the enriched oxygen content on the surface was decreased. For the hot-pressed specimens, the highest oxygen content was 519 ppm an the oxygen-rich area lies along the grain boundaries. As the oxygen content decreased, the carrier mobility (mu) was increased and the electrical resistivity (p) was decreased. The reduction of oxygen content by the reduction process using hydrogen gas causes the increase of mu, leading to high value of figure of merit (Z). For the specimens containing the oxygen content of 79 ppm, the maximum Z value of 3.4 x 10(-3) K-1 was obtained. There was a tendency for grain size to increase with increasing oxygen content in the hot-pressed specimens.