Band engineering and improved thermoelectric performance in p-type SmMg2Sb2: A first-principles study

Abstract

The thermoelectric properties of p-type SmMg2Sb2 are investigated by using the density functional theory and the Boltzmann transport equation method. It is found that SmMg2Sb2 shows a narrow band gap characteristic, and the crystal field splitting and spin-orbital coupling effect result in a singly degenerate valence band maximum. Meanwhile, SmMg2Sb2 exhibits an intrinsic low lattice thermal conductivity owing to the obvious phonon softening in the low-frequency acoustic branches. Based on a careful analysis of the band structure, we propose a scheme of metallic dopant at Sm site to promote the valence band convergence and improve the Seebeck coefficient. The improved thermoelectric properties are numerically confirmed in the Ba-doped p-type SmMg2Sb2, where a significantly improved ZT of 1.6 at 750 K is predicted with the synergistical effects of band engineering and enhanced phonon scattering.