Band convergence boosted high thermoelectric performance of Zintl compound Mg3Sb2 achieved by biaxial strains

Abstract

Mg3Sb2 as a Zintl compound is a promising thermoelectric material with the intrinsically low lattice thermal conductivity and excellent n-type electrical properties, but its p-type electrical transport properties are poor. Here, the thermoelectric performance of Mg3Sb2 under the effect of biaxial strain is investigated by using first-principles method and Boltzmann transport theory. The application of biaxial strain enables tuning the band structure of Mg3Sb2 in such a way that the band degeneracy of both the conduction band and valence band increases. As the biaxial strain increases, the Seebeck coefficient of p-type Mg3Sb2 has a remarkable increase, leading to a significant improvement in power factor. This is mainly ascribed to the achievement of valence band orbital degeneracy. Meanwhile, the lattice thermal conductivity exhibits very slight biaxial strain dependence within the strain range considered in this work, which increases from 1.28 to 1.62 W m−1 K−1 at 300 K. Finally, the highest ZT of p-type Mg3Sb2 at 700 K can be up to 2.6 along the in-plane direction under −2.5% biaxial strain, which is almost three times that of the unstrained counterpart. The realization of high thermoelectric performance of p-type Mg3Sb2 will promote its practical applications as thermoelectric generators.