Mg-Defect Compensation to Realize High Performance at Room Temperature in Mg₃Bi₂-Based Thermoelectric Single Crystals

Mg 3 Bi 2 -based materials are a very promising substitute for current commercial Bi 2 Te 3 thermoelectric alloys. The successful growth of Mg 3 Bi 2 -based single crystals with high room-temperature performance is especially significant for practical applications. Previous studies indicated that the effective suppression of Mg defects in Mg 3 Bi 2 -based materials was crucial for high performance, which was usually realized by applying excessive Mg during syntheses. However, utilization of excessive Mg generates Mg-rich phases between the crystalline boundaries and is unfavorable for the long-term stability of the materials. Here, bulk single crystals with a low-content Mg component such as Mg 3.1 Bi 1.49 Sb 0.5 Te 0.01 were successfully grown. For compensating Mg defects, Li was chosen as the additional electron dopant. The results indicate that Li is a very effective electron compensator when low-concentration doping is applied. For high-concentration doping, Mg atoms in the lattice are substituted by Li, leading to decreased electron concentration again. This strategy is very significant for improving the room-temperature performance of Mg 3 Bi 2 -based materials. As a result, a record-high figure of merit of 1.05 at 300 K is achieved for Mg 3+ x Li 0.003 Bi 1.49 Sb 0.5 Te 0.01 single crystals.