Theory of thermoelectricity in Mg$_3$Sb$_2$ with an energy- and temperature-dependent relaxation time

TL;DR

This study models the thermoelectric properties of Mg$_3$Sb$_2$ considering energy- and temperature-dependent scattering, showing ZT can reach 1.6 at 700 K with optimal doping, aligning well with experimental data.

Contribution

It introduces a detailed theoretical approach incorporating energy- and temperature-dependent relaxation times and ab initio lattice thermal conductivity for Mg$_3$Sb$_2$.

Findings

ZT reaches 1.6 at 700 K

Optimal doping is around 3×10^{19} cm^{-3}

ZT exceeds 1 above 500 K

Abstract

We study the electronic transport coefficients and the thermoelectric figure of merit ZT in $n$-doped Mg$_3$Sb$_2$ based on density-functional electronic structure and Bloch-Boltzmann transport theory with an energy- and temperature-dependent relaxation time. Both the lattice and electronic thermal conductivities affect the final ZT significantly, hence we include the lattice thermal conductivity calculated ab initio. Where applicable, our results are in good agreement with existing experiments, thanks to the treatment of lattice thermal conductivity and the improved description of electronic scattering. ZT increases monotonically in our T range (300 to 700 K), reaching a value of 1.6 at 700 K; it peaks as a function of doping at about 3$\times$10$^{19}$ cm$^{-3}$. At this doping, ZT$>$1 for T$>$500 K.