The Synthesis and Thermoelectric Properties of the n-Type Solid Solution Bi_2-xSb_xTe₃ (x < 1)

Commercial Peltier cooling devices and thermoelectric generators mostly use bismuth telluride-based materials, specifically its alloys with Sb₂Te₃ for the p-type legs and its alloys with Bi₂Se₃ for the n-type legs. If the p-type materials perform with zT well above the unity around room temperature, the n-type counterpart is lacking efficiency in this temperature range, and has the disadvantage of containing selenium. Indeed, despite the fact that selenium is not environmentally benign and that its handling requires precautions, the use of selenium does not facilitate the optimization of thermoelectric performance at or around room temperature, as the presence of selenium results in a larger band gap. In this study, we investigate the feasibility of a selenium-free n-type (Bi, Sb)₂Te₃ using a simple two-step process: mechanical alloying synthesis followed by spark plasma sintering. All the members of the solid solution Bi_2-xSb_xTe₃ with x < 1 are n-type materials, with zTs between 0.35 and 0.6. The zT is maximized at lower temperatures with an increasing Sb content, which is proof that the band gap is reduced accordingly. We also show here that an edge-free sintering process considerably improves thermoelectric performance.