Exceptional Performance Driven by Planar Honeycomb Structure in a New High Temperature Thermoelectric Material BaAgAs

Abstract The discovery of new, high‐performing thermoelectrics is of vital importance to promoting thermal energy conversion efficiency. Herein, a new p‐type thermoelectric material BaAgAs with an exceptional figure of merit ( zT ) surpassing 1.1 at 970 K is present as a promising candidate for high‐temperature applications. Verified by comprehensive experimental and theoretical investigations, BaAgAs possesses two intrinsic features in favoring zT : i) low lattice thermal conductivity, ascribed to the heavy element Ba in a loose mono‐hexagonal layer, the large mass fluctuation in the Ag‐As honeycomb layer, and the alternately interlayer stacking between mono‐hexagonal and honeycomb layers; ii) good electrical properties contributed by multiple band transport, due to the small band offset between two valence band extremums and the strong anisotropic band effective mass. With enhanced phonon–phonon scattering via Sb/Bi substitution on the As sites, the lattice thermal conductivity is minimized, which results in significantly enhanced zT values. Additionally, an inspiring prediction via the first‐principles calculation suggests that n‐type BaAgAs can potentially outperform its p‐type counterpart due to its higher conducting band degeneracy. This study will stimulate intense interests in the exploration of compounds with planar honeycomb structures as new high‐performance thermoelectric materials.