Band engineering and crystal field screening in thermoelectric Mg3Sb2

Abstract

Recently, Mg₃Sb₂ attracted much research interest due to its competitive thermoelectric performance of ZT = 1.7 observed in n-type materials at 700 K. On the other hand, the thermoelectric performance of p-type Mg₃Sb₂ is found to be limited (ZT < 0.7) by the low power factor, originating in the less degenerate valence valleys. In this paper, we report a systematic theoretic investigation on the thermoelectric properties of Mg₃Sb₂ by using band structure and transport calculations. Starting with the careful analysis of the band structure, the characteristics of the valence and conduction bands are clarified. By raising the concept of crystal field screening, a scheme to increase the degeneracy of valence valleys is proposed. The expected band convergence is numerically confirmed in Ba-doped p-type Mg₃Sb₂, where a significantly improved ZT = 1.2 at 800 K is predicted. This study provides an applicable scheme for improving the thermoelectric performance of Mg₃Sb₂, and also it enriches the concept of band engineering for thermoelectrics.