Quasi-2D Carrier Transport in KMgBi for Promising Thermoelectric Performance

KMgBi is an interesting system with several unconventional electronic transport properties. Despite numerous studies exploring its topological trivial/nontrivial nature, it has never been studied from a thermoelectric (TE) perspective. Its band structure shows appropriate degenerate flat bands near the valence band edge that are useful for high thermopower. We also show that KMgBi acquires a high degree of anharmonicity that leads to low lattice thermal conductivity. This yields a high TE figure of merit, ZT ∼ 2.21 (p-type) at ∼600 K temperature. A careful analysis of electron and phonon dispersion establishes an interesting quasi-2D nature of KMgBi. Utilizing the flat degenerate valence band and strong spin–orbit coupling, we discuss how to further enhance the TE performance of KMgBi via alloy engineering. Substituting Li at K and As at Bi sites increases the band gap with little effect on the band curvature, further improving the TE performance. With 50% As alloying, we expect ∼10–11% enhancement in the ZT.