Effect of group-3 elements doping on promotion of in-plane Seebeck coefficient of n-type Mg3Sb2

Mg3Sb2-based alloys are promising thermoelectric materials with a reasonably low thermal conductivity. However, their electrical transport property is usually limited by the low carrier concentration. Mg3Sb2 has a multi-valley conduction band with a six-fold degeneracy, benefiting n-type thermoelectric performance. Recently, n-type Y-doped Mg3Sb1.5Bi0.5 and Sc-doped Mg3Sb2Mg3Bi2 alloys show a large figure of merit (ZT). In this paper, the doping effect of group-3 and chalcogen elements on the electronic structures and electrical transport properties of Mg3Sb2 was investigated via the first-principles calculations. Chalcogen elements have a slight effect on the electronic structure, and Te-doped Mg3Sb2 shows better normalized power factors in both the out-of-plane and in-plane directions, compared to the S-doped and Se-doped systems. Distinctly different doping effects appear in Mg3Sb2 doped with group-3 elements. A increased density of states near the bottom of the conduction band can be induced by Sc or Y. Sc-doped and Y-doped Mg3Sb2 show higher normalized power factors along the in-plane direction than those doped with chalcogens.