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

Abstract

n-type Mg3Bi2-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 Mg3Bi2. Compared to the undoped sample, a nearly three-times enhancement in ZT was achieved at 300 K for Mg3Bi1.99Se0.01, which can be attributed to the significantly increasing power factor (PF). The PF increased from 10 to 30 µW cm−1 K−2. The improved PF mainly benefited from the high Seebeck coefficient (150–160 µV K−1 at room temperature), which resulted from band convergence induced by Se doping. To further improve the thermoelectric performance, Mg3Bi1.99Se0.01 alloying with Mg3Sb2 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 Mg3.2Bi1.09Sb0.9Se0.01 sample.