Single-crystalline Mg₃Sb_2-xBi_x-based thermoelectric materials

N-type Mg₃Sb_2-xBi_x-based materials have become promising candidates for thermoelectric cooling and power generation. Most recently, Mg₃Sb_2-xBi_x single crystals have been successfully grown; these demonstrate superior thermoelectric performance and are essential to understanding electron and phonon transport. In this perspective, recent progress on single-crystalline Mg₃Sb_2-xBi_x-based thermoelectric materials is reviewed. Firstly, methods to grow Mg₃Sb_2-xBi_x single crystals are briefly introduced. Then, a comparison of electrical properties between the single-crystalline samples and polycrystalline counterparts is discussed. Afterward, theoretically calculated and experimentally identified point defects, along with their impact on the transport properties, are summarized. Moreover, the structural and thermoelectric anisotropy in Mg₃Sb_2-xBi_x single crystals is discussed. Finally, the perspective concludes with an outlook on the existing challenges and opportunities in Mg₃Sb_2-xBi_x-based thermoelectric materials and devices.