Improving Thermoelectric Performance of α-MgAgSb by Theoretical Band Engineering Design

alpha-MgAgSb is recently discovered to be a new class of thermoelectric material near room temperature. A competitive ZT of 1.4 at 525 K is achieved in Ni-doped alpha-MgAgSb, and the measured efficiency of energy conversion reaches a record value of 8.5%, which is even higher than that of the commercially applied material bismuth telluride. On the other hand, the band structure of alpha-MgAgSb is believed to be unprofitable to the power factor, owing to the less degenerate valence valleys. Here, this paper reports a systematic theoretical study on the thermoelectric properties by using the electron/phonon structure and transport calculations. Based on the careful analysis of Fermi surface, a principled scheme is presented to design band engineering in alpha-MgAgSb. Following the given rules, several effective dopants are predicted. As two examples, Zn- and Pd-doped alpha-MgAgSb are numerically confirmed to exhibit an extraordinary ZT value of 2.0 at 575 K and a high conversion efficiency of 12.6%, owing to the effects of band convergence. This work develops an applicable scheme for the purposive design of band engineering, and the idea can be simply applied to more thermoelectric materials.