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 Mg3LaxSbBi (0 ≤ <i>x</i> ≤ 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 Mg3LaxSbBi increased linearly with La content <i>x</i>, reaching up to 9.4 × 10¹⁹ cm^-3 at <i>x</i> = 0.02. The power factor and the figure of merit were also maximized in Mg3La0.02SbBi, 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 Mg3La0.02SbBi. This study shows that La doping using LaSb provides a reliable method for n-type doping of Mg3Sb2-based materials.