Manipulation of ionized impurity scattering for achieving high thermoelectric performance in n-type Mg₃Sb₂-based materials

Achieving higher carrier mobility plays a pivotal role for obtaining potentially high thermoelectric performance. In principle, the carrier mobility is governed by the band structure as well as by the carrier scattering mechanism. Here, we demonstrate that by manipulating the carrier scattering mechanism in n-type Mg₃Sb₂-based materials, a substantial improvement in carrier mobility, and hence the power factor, can be achieved. In this work, Fe, Co, Hf, and Ta are doped on the Mg site of Mg_3.2Sb_1.5Bi_0.49Te_0.01, where the ionized impurity scattering crosses over to mixed ionized impurity and acoustic phonon scattering. A significant improvement in Hall mobility from ∼16 to ∼81 cm²·V⁻¹·s⁻1 is obtained, thus leading to a notably enhanced power factor of ∼13 μW·cm⁻¹·K⁻² from ∼5 μW·cm⁻¹·K⁻². A simultaneous reduction in thermal conductivity is also achieved. Collectively, a figure of merit (ZT) of ∼1.7 is obtained at 773 K in Mg_3.1Co_0.1Sb_1.5Bi_0.49Te_0.01. The concept of manipulating the carrier scattering mechanism to improve the mobility should also be applicable to other material systems.