Crystal structure, electronic structure and thermoelectric properties of n-type BiSbSTe ₂

N-type bismuth telluride sulfide has received attention as a potential thermoelectric material due to its large thermopower and ability to form solid solutions with bismuth antimony sulfide. Here, we fabricated an n-type tetradymite BiSbSTe ₂ by solid-state reaction. The crystal structure was found to be rhombohedral, and the thermoelectric properties were measured for the temperature range 50-390K. A high Seebeck coefficient of 190νVK ^-1 was achieved at 385K. The electronic structure of BiSbSTe ₂ was investigated using first-principles calculations and compared with its parent counterpart (Bi ₂STe ₂). The results have shown that BiSbSTe ₂ is a narrow band-gap semiconductor. For the first time, we have demonstrated that the vacancies in substitutional atomic sites, which can be altered through different fabrication techniques, can determine the charge carrier nature of tetradymite thermoelectrics. As a proof of concept, we have shown that the vacancies in antimony sites result in a p-type compound while a sulfur deficiency produces an n-type phase with lower electrical conductivity.