Mechanical Compatibility between Mg<sub>3</sub>(Sb,Bi)<sub>2</sub> and MgAgSb in Thermoelectric Modules
Yifan Sun, Jiahui Fu, Yuji Ohishi, Keita Toh, Koichiro Suekuni, Kunihiro Kihou, Ushin Anazawa, Chul‐Ho Lee, Ken Kurosaki
Abstract
Thermoelectric (TE) modules are exposed to temperature gradients and repeated thermal cycles during their operation; therefore, mechanically robust n- and p-type legs are required to ensure their structural integrity. The difference in the coefficients of thermal expansion (CTEs) of the two legs of a TE module can cause stress buildup and the deterioration of performance with frequent thermal cycles. Recently, n-type Mg 3 Sb 2 and p-type MgAgSb have become two promising components of low-temperature TE modules because of to their high TE performance, nontoxicity, and abundance. However, the CTEs of n-Mg 3 Sb 2 and p-MgAgSb differ by approximately 10%. Furthermore, the oxidation resistances of these materials at increased temperatures are unclear. This work manipulates the thermal expansion of Mg 3 Sb 2 by alloying it with Mg 3 Bi 2 . The addition of Bi to Mg 3 Sb 2 reduces the coefficient of linear thermal expansion from 22.6 × 10 –6 to 21.2 × 10 –6 K –1 for Mg 3 Sb 1.5 Bi 0.5, which is in excellent agreement with that of MgAgSb (21 × 10 –6 K –1 ). Furthermore, thermogravimetric data indicate that both Mg 3 Sb 1.5 Bi 0.5 and MgAgSb are stable in air and Ar at temperatures below ∼570 K. The results suggest the compatibility and robustness of Mg 3 Sb 1.5 Bi 0.5 and MgAgSb as a pair of thermoelectric legs for low-temperature TE modules.