The electronic structure and thermoelectric properties of BiTl9Te6 and SbTl9Te6: First-principles calculations

Abstract

The electronic structure and thermoelectric properties of MTl9Te6 (M = Bi, Sb) were studied using density functional theory and the semiclassical Boltzmann theory. It is found that the band gaps of BiTl9Te6 and SbTl9Te6 are equal to 0.59 eV and 0.72 eV, respectively. The relative large band gap and strong coupling between Sb s and Te p are helpful to the thermoelectric properties of SbTl9Te6. Near the bottom of the conduction bands, the number of band valleys of SbTl9Te6 is four and is larger than that of BiTl9Te6 (two band valleys), which will increase its Seebeck coefficient. Although BiTl9Te6 has a larger electrical conductivity relative to relaxation time (σ/τ) along the z-direction than that of SbTl9Te6, the results show that the transport properties of SbTl9Te6 are better than those of BiTl9Te6 possibly due to its large Seebeck coefficient. The maximum value of power factor relative to relaxation time (S2σ/τ) for SbTl9Te6 reaches 4.30 × 1011 W/K2 m s at 900 K, that is, originated from its relatively large Seebeck coefficient, suggesting its promising thermoelectric performance at high temperature.