Using first-principles density-functional theory calculations, we predict the potential for unprecedented thermoelectric efficiency zT=5 at 800 K in n-type Ba2BiAu full-Heusler compound. Such a high efficiency arises from an intrinsically ultralow lattice thermal conductivity coupled with a very high power factor reaching 7 mW m−1 K−2 at 500 K. The high power factor originates from a light, sixfold degenerate conduction band pocket along the Γ-X direction. Weak acoustic phonon scattering and sixfold multiplicity combine to yield high mobility and high Seebeck coefficient. In contrast, the flat-and-dispersive (a.k.a. low-dimensional) valence band of Ba2BiAu fail to generate a high power factor due to strong acoustic phonon scattering. The Lorenz numbers at optimal doping are smaller than the Wiedemann-Franz value, an integral feature for zT enhancement as electrons are the majority heat carriers.
@article{arxiv.1804.09392,
title = {High $n$-type thermoelectric power factor and efficiency in Ba$_{2}$BiAu from a highly dispersive band},
author = {Junsoo Park and Yi Xia and Vidvuds Ozoliņš},
journal= {arXiv preprint arXiv:1804.09392},
year = {2019}
}