High $n$-type thermoelectric power factor and efficiency in Ba$_{2}$BiAu from a highly dispersive band

TL;DR

This study predicts that n-type Ba₂BiAu full-Heusler compounds can achieve an unprecedented thermoelectric efficiency of zT=5 at 800 K, due to a combination of high power factor and ultralow thermal conductivity.

Contribution

The paper demonstrates, through first-principles calculations, that Ba₂BiAu exhibits a highly dispersive conduction band leading to exceptional thermoelectric performance, a novel insight for full-Heusler materials.

Findings

Predicted zT of 5 at 800 K in Ba₂BiAu

High power factor of 7 mW/mK² at 500 K

Ultralow lattice thermal conductivity

Abstract

Using first-principles density-functional theory calculations, we predict the potential for unprecedented thermoelectric efficiency $zT=5$ at 800 K in $n$-type Ba$_{2}$BiAu 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 $\Gamma$-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 Ba$_{2}$BiAu 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.