A two-step synthesis process of thermoelectric alloys for the separate control of carrier density and mobility

It is challenging to improve the thermoelectric figure-of-merit as its constituent terms such as Seebeck coefficient, electrical conductivity, and thermal conductivity, are inter-related in the way that the enhancement of one term leads to the degradation of others. Therefore, it is highly desirable to design a new synthesis process that allows us to independently control these terms. Here, we report a simple, two-step process combining spark plasma sintering (SPS) and post-annealing (PA) to separately control the carrier density and mobility in the p-type (Bi_0.2Sb_0.8)₂Te₃. High-temperature SPS enables enhancing the carrier mobility by reducing scattering sites such as grain boundaries. Then, the following PA at a lower temperature allows tailoring the carrier density without the degradation of mobility. Beyond bismuth telluride-based, room-temperature thermoelectric materials, we believe that our result will provide an insight for the performance enhancement of other thermoelectric materials such as oxide and skutterudite.