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 SmMg2Sb2 with high thermoelectric performance has been realized. Density functional theory calculations indicate that the conduction bands extrema of SmMg2Sb2 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 (-2.6m0) compared to that of many p-type Zintl phases. With the optimization of the electron concentration, an n-type power factor -11.0 mu W cm-1 K-2 is obtained in SmMg2+delta Sb1.97Te0.03 (delta = 0.3). Together with the effectively reduced lattice thermal conductivity by further alloying of SmMg2Bi2, a peak zT -1.0 at 873 K is achieved in n-type SmMg2+delta Sb1.72Bi0.25Te0.03 (delta = 0.3), demonstrating the great potential of ntype Zintl phase thermoelectric materials.