Thermoelectric properties of topological insulator $\mathrm{BaSn_2}$

Abstract

Recently, $\mathrm{BaSn_2}$ is predicted to be a strong topological insulator by the first-principle calculations. It is well known that topological insulator has a close connection to thermoelectric material, such as $\mathrm{Bi_2Te_3}$ family. In this work, we investigate thermoelectric properties of $\mathrm{BaSn_2}$ by the first-principles combined with Boltzmann transport theory. The electronic part is carried out by a modified Becke and Johnson (mBJ) exchange potential, including spin-orbit coupling (SOC), while the phonon part is performed using generalized gradient approximation (GGA). It is found that the electronic transport coefficients between the in-plane and cross-plane directions show the strong anisotropy, while lattice lattice thermal conductivities show an almost isotropy. Calculated results show a very low lattice thermal conductivity for $\mathrm{BaSn_2}$, and the corresponding average lattice thermal conductivity at room temperature is 1.69 $\mathrm{W m^{-1} K^{-1}}$, which is comparable or lower than those of lead chalcogenides and bismuth-tellurium systems as classic thermoelectric materials. Due to the complicated scattering mechanism, calculating scattering time $\tau$ is challenging. By using a empirical $\tau$=$10^{-14}$ s, the n-type figure of merit $ZT$ is greater than 0.40 in wide temperature range. Experimentally, it is possible to attain better thermoelectric performance, or to enhance one by strain or tuning size parameter. This work indicates that $\mathrm{BaSn_2}$ may be a potential thermoelectric material, which can stimulate further theoretical and experimental works.