Optimization of (Bi,Sb)/sub 2/(Te,Se)/sub 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)/sub 2/(Te,Se)/sub 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 Bi/sub 2/Te/sub 3-x-y/Se/sub x/S/sub y/ and p-type Bi/sub 2-x/Sb/sub x/Te/sub 3-y/Se/sub 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.