Bi‐Deficiency Leading to High‐Performance in Mg3(Sb,Bi)2‐Based Thermoelectric Materials

Abstract Mg 3 (Sb,Bi) 2 is a potential nearly‐room temperature thermoelectric compound composed of earth‐abundant elements. However, complex defect tuning and exceptional microstructural control are required. Prior studies have confirmed the detrimental effect of Mg vacancies (V Mg ) in Mg 3 (Sb,Bi) 2 . This study proposes an approach to mitigating the negative scattering effect of V Mg by Bi deficiency, synergistically modulating the electrical and thermal transport properties to enhance the thermoelectric performance. Positron annihilation spectrometry and C s ‐corrected scanning transmission electron microscopy analyses indicated that the V Mg tends to coalesce due to the introduced Bi vacancies (V Bi ). The defects created by Bi deficiency effectively weaken the scattering of electrons from the intrinsic V Mg and enhance phonon scattering. A peak zT of 1.82 at 773 K and high conversion efficiency of 11.3% at ∆ T = 473 K are achieved in the optimized composition of Mg 3 (Sb,Bi) 2 by tuning the defect combination. This work demonstrates a feasible and effective approach to improving the performance of Mg 3 (Sb,Bi) 2 as an emerging thermoelectric material.