Electronic Structures and Thermoelectric Properties of Layered Chalcogenide PbBi4Te7 from First Principles

Abstract

The electronic structures and the thermoelectric (TE) properties of the ternary chalcogenide PbBi4Te7 are investigated by using first-principles calculations within the density functional theory and the solutions of semi-classical Boltzmann equation. Employing the screened-exchange local density approximation, we found that PbBi4Te7 to be a narrow-gap semiconductor with an indirect band gap of 0.11 eV. The combination of light and heavy valence bands near the band edge gives rise to large Seebeck coefficients, S, for p-type doping, which is found to be improved by 11% from that of Bi2Te3 at room temperature (RT). Moreover, in contrast to conventional Bi2Te3 where the value of S decreases rapidly with temperatures higher than RT, the values of S increases with temperature reaching up to 350 mu VK-1 at 500 K indicating that PbBi4Te7 is a promising TE material with operating temperatures above RT. Our result also reveals that the intrinsic layered structure results in a prominent anisotropy in the TE coefficients, implying that the TE performance can be optimized by using the transport direction, as well as the type and the level of doping.