Synthesis and Thermoelectric Properties of La-doped n-type Mg3SbBi Materials

Mg₃Sb₂-based materials are very promising for thermoelectric applications at low temperatures, and are strong candidates to replace n-type Bi₂Te₃ for cooling and power generation. Substituting Sb atoms with chalcogen elements (S, Se, Te) is a typical method of n-type doping, while doping the Mg site with Group 3 elements (Y, Sc) and Lanthanides has also been studied. Unique advantages have been recently reported. In this study, a La-containing compound, LaSb, was used to fabricate n-type Mg₃SbBi. The thermoelectric properties of polycrystalline Mg₃La_xSbBi (0 ≤ x ≤ 0.02) were investigated after synthesis by sequential processes of arc melting, ball milling, and spark plasma sintering. Undoped Mg₃SbBi is p-type with poor thermoelectric performance, and switched to n-type with La doping. The electron concentration of Mg₃La_xSbBi increased linearly with La content x, reaching up to 9.4 × 10¹⁹ cm^-3 at x = 0.02. The power factor and the figure of merit were also maximized in Mg₃La_0.02SbBi, reaching 1.8 mW m^-1K^-2 (573 K) and 0.89 (623 K), respectively. The lattice thermal conductivity decreased with increasing La content above ~500 K, and the minimum value of 0.73 W m^-1K^-1 was obtained in Mg₃La_0.02SbBi. This study shows that La doping using LaSb provides a reliable method for n-type doping of Mg₃Sb₂-based materials.