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

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 Mg3Sb2-xGex (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 Mg3Sb1.97Ge0.03 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.