Theoretical Study on Thermoelectric Performance of N‐Type Mg₃(Sb,Bi)₂ Single Crystal for Cooling or Power Generation

Abstract

Mg 3 Sb 2 -based Zintl compounds have been paid much attention in recent years because of their high peak figure of merit (zT), however, there is room for the improvement of the average zT. In this work, the thermoelectric performance of Mg 3 (Sb,Bi) 2 single crystal by using density functional theory is investigated. The optimal carrier concentration (n) of Mg 3 SbBi is 2 × 10 19 to 3 × 10 20 cm -3 at 100−700 K. At the n of 3 × 10 19 cm -3 , it can exhibit a high average zT of ≈1.27 at cold-side temperature (T c ) of 300 K and hot-side temperature (T h ) of 700 K, and the electrical transport performance can be further improved by increasing the n. When the optimal n is reached, the maximum average zT of Mg 3 SbBi at T c of 100 K and T h of 300 K can be up to 0.54, which is comparable to that of state-of-the-art Bi 2 (Te,Se) 3 . Because the decreasing trend of the optimal n with temperature, the maximum low-temperature thermoelectric performance is easier to be achieved by less extrinsic doping. This work reveals the great potential of Mg 3 (Sb,Bi) 2 single crystal for thermoelectric cooling or power generation, which is expected to provide useful guidance for thermoelectric devices.