Multifaceted Roles of Tantalum in Promoting the Thermoelectric Performance of Mg₃(Sb,Bi)₂ Based Materials

Mg₃(Sb,Bi)₂ has emerged as one of the most promising thermoelectric materials with the potential to complement commercial bismuth telluride. However, its performance is still hindered by pronounced carrier grain-boundary scattering, relatively high lattice thermal conductivity, and poor chemical stability. In this work, we reveal the multifaceted role of Ta in enhancing the thermoelectric performance of Mg₃(Sb,Bi)₂-based materials. The incorporation of Ta not only increases carrier concentration through the donor effect, but also boosts carrier mobility by promoting grain growth and reducing the potential barrier. Meanwhile, Ta point defects together with metallic Ta precipitates induce strong phonon scattering, leading to a substantial reduction in lattice thermal conductivity. These synergistic effects yield outstanding TE performance, with a remarkably high zT plateau of 1.8 between 573 and 723 K, surpassing the performance of most previously reported Mg₃(Sb,Bi)₂ systems. Moreover, a TE module constructed by both p-type and n-type Zintl phases achieves a high conversion efficiency of 9.6% at ΔT of 460 K. This work takes an important step toward the practical application of Mg₃Sb₂-based TE materials and devices.