Enhanced thermoelectric performance of a p-type Mg3Sb2-based Zintl phase compound via Ge doping

Abstract

Mg₃Sb₂-based thermoelectric materials are considered promising due to their non-toxic and cost-effective characteristics. Despite the low intrinsic thermal conductivity of these materials, their thermoelectric performance is significantly limited by a low carrier concentration. First principle calculations on p-type Mg₃Sb₂-based materials suggest that doping Ge at the Sb sites can notably enhance carrier concentration. Consequently, through vacuum melting combined with spark plasma sintering (SPS), samples of p-type Mg₃Sb_2-xGe_x (0≤x ≤ 0.05) were prepared. All Ge-doped samples display an increased carrier concentration, leading to a significant increase in the electrical conductivity and power factor (PF). Interestingly, the effect of Ge doping on thermal conductivity is minimal, making the Mg₃Sb_1.97Ge_0.03 sample reaches the maximum thermoelectric figure of merit of 0.39 at 723 K, a fivefold increase compared to the undoped sample. This substantiates the efficacy of Ge as an efficient p-type dopant.