Significant Roles of Intrinsic Point Defects in Mg2X (X = Si, Ge, Sn) Thermoelectric Materials

Point defects play a decisive role in the physical properties of thermoelectric materials and have been adopted as a new strategy to enhance thermoelectric properties. Here, the kinds of defects formed in Mg 2 X ( X = Si, Ge, Sn) compounds are discussed and their influence mechanism on the thermoelectric performance by first‐principles calculation is understood. Mg vacancies and interstitial Mg are found to be the dominant defects and their competition directly determines the different intrinsic conduction of Mg 2 X . Mg 2 Si always shows n‐type, no matter what the Mg chemical potential is, while the conduction of Mg 2 Ge and Mg 2 Sn can change from p‐type to n‐type with increasing Mg chemical potential (Mg‐rich condition). Interestingly it is also found that interstitial Mg shares electrons with lattice Mg, changes the charge density distribution, and produces the impurity‐like level below the conduction band minimum. These results are helpful for understanding the roles of point defects in Mg 2 X and other thermoelectric compounds.