N-Type Mg₃Sb_2- Bi Alloys as Promising Thermoelectric Materials

N-type Mg₃Sb_2- Bi alloys have been extensively studied in recent years due to their significantly enhanced thermoelectric figure of merit (zT), thus promoting them as potential candidates for waste heat recovery and cooling applications. In this review, the effects resulting from alloying Mg₃Bi₂ with Mg₃Sb₂, including narrowed bandgap, decreased effective mass, and increased carrier mobility, are summarized. Subsequently, defect-controlled electrical properties in n-type Mg₃Sb_2- Bi are revealed. On one hand, manipulation of intrinsic and extrinsic defects can achieve optimal carrier concentration. On the other hand, Mg vacancies dominate carrier-scattering mechanisms (ionized impurity scattering and grain boundary scattering). Both aspects are discussed for Mg₃Sb_2- Bi thermoelectric materials. Finally, we review the present status of, and future outlook for, these materials in power generation and cooling applications.