Boosting the Thermoelectric Performance of α -MgAgSb through Phase-Transition-Induced Self-Doping

In thermoelectric (TE) and other functional electronic materials, chemical doping is commonly employed to tune the carrier density toward an optimal Fermi level and, in turn, maximize the electrical transport. However, in some systems, such as the emerging high-performance p -type TE material α -MgAgSb, chemical doping is challenging due to its weak chemical bonds and extremely low solubility of heteroatomic dopants, which makes it difficult to increase the hole carrier density and realize the otherwise predictable improvements in the TE power factor. Here, we report a doping-free strategy to enhance the TE performance of α -MgAgSb by utilizing a phase-transition-induced self-doping process. Annealing at the phase-transition temperature of 593 K lowers the formation energy of Ag vacancies in the high-temperature β phase, and these vacancies are subsequently retained upon cooling back to the α phase. As a result, the hole concentration increases markedly from 4.5 × 10 19 to 1.3 × 10 2 0 cm − 3 , activating multiple valence bands and boosting the room-temperature power factor by ∼ 35 % to 30 μ W cm − 1 K − 2 . A single-leg device fabricated from the optimized material achieves a high conversion efficiency of 10.7% and a maximum output power of 71.1 mW at Δ T = 2 8 5 K . This work demonstrates a viable pathway for enhancing TE performance via phase-transition engineering.