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

Mg₃Bi₂-based materials are a very promising substitute for current commercial Bi₂Te₃ thermoelectric alloys. The successful growth of Mg₃Bi₂-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 Mg₃Bi₂-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_3.1Bi_1.49Sb_0.5Te_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 Mg₃Bi₂-based materials. As a result, a record-high figure of merit of 1.05 at 300 K is achieved for Mg₃₊Li_0.003Bi_1.49Sb_0.5Te_0.01 single crystals.