Optimization of (Bi,Sb)2(Te,Se)3-based thermoelectrics for low-temperature applications

General situation with thermoelectric cooling at temperatures below 200 K is discussed. The problem of optimization of (Bi,Sb)₂ (Te,Se)₃-based thermoelectrics for operation in this temperature range is distinguished as the actual one especially in connection with a possible practical application of high-temperature superconductors. Then detailed results of the first systematic study of n-type Bi₂Te_3-x-ySe_xS_y and p-type Bi_2-xSb_xTe_3-ySe_y are presented. The composition of solid solutions and the current carrier concentration were optimized. Thermopower, electrical and thermal conductivity were measured at 80-350 K, and thermoelectric figure of merit was calculated. Figure of merit for both type materials was increased significantly for the temperatures near 100-150 K. These optimized materials were used for the fabrication of the special low-temperature thermoelectric modules. These modules were tested, and temperature 130 K and 124 K on the cold junction of 2 types of 6-stages coolers was achieved