Enhanced thermoelectric performance of n-type Mg3Bi2-based materials by Se doping and alloying engineering

Abstract n-type Mg 3 Bi 2 -based materials have been considered to be a promising near-room-temperature thermoelectric material and have recently received a great deal of attention. In this paper, we first investigated the thermoelectric properties of Se doped Mg 3 Bi 2 . Compared to the undoped sample, a nearly three-times enhancement in ZT was achieved at 300 K for Mg 3 Bi 1.99 Se 0.01 , which can be attributed to the significantly increasing power factor (PF). The PF increased from 10 to 30 µ W cm −1 K −2 . The improved PF mainly benefited from the high Seebeck coefficient (150–160 µ V K −1 at room temperature), which resulted from band convergence induced by Se doping. To further improve the thermoelectric performance, Mg 3 Bi 1.99 Se 0.01 alloying with Mg 3 Sb 2 has been explored. The results show that band gap of alloy increased with the increasing Sb ratio. Meanwhile, the effective scattering of phonon due to Bi/Sb disorder lead to the decrease of lattice thermal conductivity. Finally, a peak ZT of 1.3 at 525 K and average ZT of 1.02 in the temperature range of 300–525 K were obtained in Mg 3.2 Bi 1.09 Sb 0.9 Se 0.01 sample.