First-principles Study of Metallic-atom Diffusion in Thermoelectric Material Mg$_3$Sb$_2$

TL;DR

This study uses first-principles calculations to analyze how metallic atoms diffuse in Mg$_3$Sb$_2$, revealing insights into impurity behavior and diffusion barriers relevant for thermoelectric device development.

Contribution

It provides the first detailed computational analysis of metallic-atom diffusion and defect formation energies in Mg$_3$Sb$_2$, highlighting elements with low formation energies and diffusion barriers.

Findings

Ni has a very low defect formation energy and diffuses in the ab plane at high temperatures.

Cu has a higher defect formation energy but a low diffusion barrier in the ab plane.

Early transition metals with large atomic radii have high defect formation energies.

Abstract

Mg$_3$Sb$_2$ is a promising thermoelectric material that consists of nontoxic and earth-abundant elements. We investigate metallic-atom diffusion in Mg$_3$Sb$_2$ by calculating the defect formation energy and the diffusion energy barrier for several kinds of metallic-atom impurities. We find that early transition metals, including $4d$ elements, with a large atomic radius have a high defect formation energy, whereas Mg and late transition metals such as Ni, Cu, and Zn have relatively low formation energies as interstitial impurities. Interstitial Ni, which is found to have a very low defect formation energy, might diffuse in the $ab$ plane at high temperatures with the energy barrier of 0.7 eV, while it seems difficult to diffuse in the $c$ direction. Interstitial Cu has a higher defect formation energy than Ni but has a low energy barrier of $\sim$0.4 eV for diffusion in the $ab$ plane. This study will offer important knowledge for developing a thermoelectric device of Mg$_3$Sb$_2$.