Optimization of Thermoelectric Property of n-Type Mg₃Sb₂ Near Room Temperature via Mn&Se Co-Doping

The Bi₂Te₃ family has been considered a state-of-the-art thermoelectric material for room-temperature applications for over half a century. However, scarcity of the material Te has been a persistent issue. Recently, the discovery of n-type Mg₃(Bi, Sb)₂-based materials provides new hope for replacing traditional Bi₂Te₃, but their thermoelectric properties near room temperature still need improvement for application to practical devices. Herein, a competitive figure of merit of ≈0.8 at 300 K and a high power factor greater than 30 µW cm⁻¹ K⁻² at 300 K in n-type Mg_3.14Mn_0.06Bi_1.4Sb_0.59Se_0.01 is reported, benefiting from the rationally tuned carrier concentration of 2.29×10¹⁹ cm⁻³ at room temperature. Substituting the Mg site with Mn in Mg_3.2Bi_1.4Sb_0.59Se_0.01 changes the dominant carrier scattering mechanism from a mixed scattering of acoustic phonons and ionized impurities to acoustic phonon scattering. Mn doping in Mg_3.2Bi_1.4Sb_0.59Se_0.01 also enhances the mobility to 180 cm² V⁻¹ s⁻¹, reduces the thermal conductivity, and significantly increases the quality factor β of the material. The high room temperature thermoelectric performance of n-type Mn&Se co-doped Mg₃(Bi, Sb)₂-based materials makes them a highly competitive substitute for commercialized n-type Bi₂Te₃.