High thermoelectric performance in BaAgYTe3 via low lattice thermal conductivity induced by bonding heterogeneity

Solid-state technology based on thermoelectric (TE) materials enables the conversion of heat into electricity offering an environmentally friendly solution to energy conservation. Here, we use density functional theory calculations to show that BaAgYTe3, a layered semiconductor, exhibits low lattice thermal conductivity (κl) and a high thermoelectric figure of merit. Our calculations reveal that the presence of bonding inhomogeneity, resulting from the coexisting rigid and fluctuating sublattices, favorably helps in both the electronic and phonon transports. We show that low κl in this compound mainly originates from (a) the small group velocities of the acoustic modes, (b) quasilocalized low-frequency optical phonons that give rise to multiple scattering channels, and (c) strong lattice anharmonicity. While the calculations of the atomic displacement parameters and bonding analysis reveal relatively weaker bonding of Ag atoms and establish the heterogeneity in the chemical bonding, the strong anharmonicity is manifested in the large mode Gruneisen parameters. Thus, our work provides a theoretical prediction that warrants experimental verification and should encourage further exploration of potential TE materials in the same crystal family.