Strong doping effects of group-3 elements for promoting the in-plane Seebeck coefficient of n-type Mg3Sb2: An ab inito study

Abstract Mg3Sb2-based alloys are promising thermoelectric materials with reasonably low thermal conductivity; however, their electrical transport property is usually limited by the low carrier concentration. Mg3Sb2 has mKulti-valley conduction band with a six-fold degeneracy, benefiting n-type thermoelectric performance. Recently, n-type Y-doped Mg3Sb1.5Bi0.5 and Sc-doped Mg3Sb2 Mg3Bi2 alloys have been shown to have a large figure of merit (ZT). Herein, we perform first-principles calculations to study the doping effects of group-3 and chalcogen elements on the electronic structures and electrical transport properties of Mg3Sb2. Chalcogen elements are found to have a minor effect on the electronic structure, and Te-doped Mg3Sb2 shows better normalized power factors in both the out-of-plane and in-plane directions comparing to the S-doped and Se-doped systems. Distinctly different doping effects are observed in Mg3Sb2 doped with group-3 elements. A large increase of 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.