New Insight on Tuning Electrical Transport Properties via Chalcogen Doping in n‐type Mg₃Sb₂‐Based Thermoelectric Materials

Abstract n‐type Mg₃Sb_1.5Bi_0.5 has recently been discovered to be a promising thermoelectric material, yet the effective n‐type dopants are mainly limited to the chalcogens. This may be attributed to the limited chemical insight into the effects from different n‐type dopants. By comparing the effects of different chalcogen dopants Q (Q = S, Se, and Te) on thermoelectric properties, it is found that the chalcogen dopants Q become more efficient with decreasing electronegativity difference between Q and Mg, which is mainly due to the increasing carrier concentration and mobility. Using density functional theory calculations, it is shown that the improving carrier concentration originates from the increasing doping limit induced by the stabilizing extrinsic defect. Moreover, the increasing electron mobility with decreasing electronegativity difference between Q and Mg is attributed to the smaller effective mass resulting from the enhancing chemical bond covalency, which is supported by the decreasing theoretical density of states. According to the above trends, a simple guiding principle based on electronegativity is proposed to shed new light on n‐type doping in Zintl antimonides.