Identifying the promising n-type SmMg2Sb2-based Zintl phase thermoelectric material

The discovery of promising thermoelectric materials has often been challenged by the doping bottleneck. As an example, the n-type Zintl phases are promising thermoelectric materials but are challenging to synthesize due to intractable cation vacancies. In this work, by incorporating excess Mg and Te doping, n-type SmMg ₂Sb ₂ with high thermoelectric performance has been realized. Density functional theory calculations indicate that the conduction bands extrema of SmMg ₂Sb ₂ are located at the L and M points in the Brillouin zone, and the valley degeneracy is 6. The high valley degeneracy of conduction bands results in a much larger n-type density-of-state effective mass (∼2.6 m ₀) compared to that of many p-type Zintl phases. With the optimization of the electron concentration, an n-type power factor ∼11.0 μW cm ⁻¹ K ⁻² is obtained in SmMg _{2+ δ}Sb _1.97Te _0.03 ( δ = 0.3). Together with the effectively reduced lattice thermal conductivity by further alloying of SmMg ₂Bi ₂, a peak zT ∼1.0 at 873 K is achieved in n-type SmMg _{2+ δ}Sb _1.72Bi _0.25Te _0.03 ( δ = 0.3), demonstrating the great potential of n-type Zintl phase thermoelectric materials.