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

Abstract Mg₃(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 Mg₃(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 Mg₃(Sb,Bi)₂ by tuning the defect combination. This work demonstrates a feasible and effective approach to improving the performance of Mg₃(Sb,Bi)₂ as an emerging thermoelectric material.