Development of cryogenic cooler based on n-type Bi-Sb thermoelectric and HTSC

Single crystals of n-Bi-Sb solid solutions with Sb content of 7–15 at.% are the most efficient thermoelectric (TE) materials over the temperature range of T ≤ 200 K. However, the use of these materials for construction of real thermoelectric devices are limited due to low mechanical strength. In this paper, for strengthening Bi-Sb single crystals, the method of the extrusion in a liquid medium under high hydrostatic pressure has been developed. The thermoelectric properties of Bi_0.91Sb_0.09 extruded crystals and single crystals were studied over the entire temperature range of 77–200 K. The high dimensionless thermoelectric figure of merit ~0.95 was obtained for the Bi_0.91Sb_0.09 single crystal measured in the transverse magnetic field. Unique thermoelectric coolers for operating temperatures below 100 K based on the n-type Bi_0.91Sb_0.09 leg and a passive leg based on a high-temperature YBa₂Cu₃O_7-x superconductor (HTSC) films have been constructed. The achieved maximum value of temperature difference ΔT = 14 K and the maximum cooling capacity Q_c = 0.4 W (the temperature of the hot side of cryogenic module T_h = 80 K, an electric current I = 6.4 A and a voltage V = 0.10 V) makes evident that using of the Bi-Sb extruded crystals in place of single crystals for the cryogenic coolers is more reasonable due to much better mechanical properties and similar values of cooling capacity.