Large improvement in thermoelectric performance of pressure-tuned Mg3Sb2

Abstract

The Mg₃Sb₂-based Zintl compound is a promising candidate for a high-performance thermoelectric material with the advantage of the component elements being low cost, non-toxic and earth-abundant. Here, we investigate the influence of pressure on the electronic structure and p-type and n-type thermoelectric transport properties of Mg₃Sb₂ by using density functional theory and Boltzmann transport theory. The energy gaps first increase and then decrease with the increasing of pressure, and a peak value of the valley degeneracy of conduction band occurs at 4 GPa. Based on the calculated band structures, the zT (figure of merit) values of p-type Mg₃Sb₂ under pressure are significantly enhanced, which predominantly originates from the boosted PF (power factor) contributed by the increased carrier's relaxation time. When the carrier concentration reaches 1 × 10²⁰ cm^-3, the PF of p-type Mg₃Sb₂ at 4 GPa is increased by 35% relative to that of the compound at 0 GPa, thus leading to a considerably improved zT of ∼0.62 at 725 K. Under the same conditions, due to the increased density of states effective mass, the n-type Mg₃Sb₂ exhibits a highest PF of ∼19 μW cm^-1 K^-2 and a peak zT of 1.7. Therefore, pressure tuning is an effective method to improve the p-type and n-type thermoelectric transport performance of Mg₃Sb₂-based Zintl compounds. This work on Mg₃Sb₂ under pressure may provide a new mechanism for the experimenters towards the enhancement of the thermoelectric performance of materials.