Electronic Properties of Low-Temperature Thermoelectric Materials: Selenium Doped Bismuth-Antimony Alloys

We explore the electronic properties of selenium doped bismuth-antimony (Bi-Sb-Se) system and present a model of the conduction band edge structure of this system. Polycrystalline Bi_1-xSb _xSe_y samples were synthesized by fusion method. The electron concentration n estimated from R_H increases with increasing Se concentration below y < 0.003, while the n is saturated in the range of Se concentration 0.003 les y les 0.1 This result indicates that the Fermi level is pinned by the Se level for the samples with y ges 0.003. We find that the values of Seebeck coefficient S for all samples change in the wide temperature range according to |S| = An ^-0.67T, the proportionality factors A being independent of Se concentration y . It confirms that the electronic properties of the Bi-Sb-Se system can be understood by three dimensional nearly free electrons in a parabolic conduction band. Based on these results, we will discuss a strategy to improve the thermoelectric performance of low-temperature thermoelectric materials