Modulation of band alignment and electron-phonon scattering in Mg3Sb2 via pressure

Abstract

It has been shown in experiments that applying hydrostatic pressure can enhance the thermoelectric performance of PbSe-based and SnSe-based alloys. Mg3Sb2 is a potential thermoelectric material with a reasonably low thermal conductivity, but its thermoelectric performance is limited by its electrical transport properties. Here, we performed density functional calculations to study the hydrostatic pressure effect on the electronic structure and the electrical transport properties of Mg3Sb2. The band gap of Mg3Sb2 exhibits a nonmonotonic change with pressure, and a band convergence with multivalley conduction states (NV = 8) is found at 5 GPa, leading to the enhancement of the density of states (DOS) near the conduction band edge. Based on the Boltzmann transport theory, it is found that both n-type and p-type Mg3Sb2 have larger power factors under pressure, but the mechanisms of each are distinctly different. In n-type Mg3Sb2 at 5 GPa, the Seebeck coefficients along both the in-plane and out-of-plane directions clearly increase due to the increased DOS effective mass near the conduction band edge, while in p-type Mg3Sb2, the electron–phonon interaction near the valence band edge is suppressed under pressure, causing a smaller electronic scattering rate and a longer electronic relaxation time.