Electronic structure and transport of Bi2Te3 and BaBiTe3

We have carried out detailed ab initio electronic structure calculations of a novel thermoelectric compound BaBiTe3 and its parent Bi2Te3, the best room-temperature thermoelectric known to date. The calculations were carried out using the self-consistent full-potential linearized augmented plane-wave method within density functional theory. The generalized gradient approximation of Perdew, Burke, and Ernzerhof was used to treat the exchange and correlation potential. For both systems, inclusion of spin-orbit interaction is crucial in understanding the gap structure near the Fermi energy. The calculated theoretical values of the gaps agree surprisingly well with experiment. A detailed comparison of the band structures of these two compounds indicates that the effective masses (expressed in units of free-electron mass) for bath of them are highly anisotropic and comparable in magnitude. They lie in the range 0.01-0.4. The major difference between the two compounds is the large degeneracy of the band extrema in Bi2Te3, which is most likely the origin of its large thermoelectric figure of merit.