Four-phonon scattering and multi-valley characteristics induce high thermoelectric performance in TlAgSe: a first-principles investigation

Abstract

Materials with intrinsically lower thermal conductivity and exceptional electrical properties are required for high-performance thermoelectric applications. The recently synthesized Zintl phase TlAgSe demonstrates lower thermal conductivity; however, it exhibits suboptimal thermoelectric performance. To gain a deeper understanding of the mechanism underlying the ultralow lattice thermal conductivity and evaluate the potential of thermoelectric performance of TlAgSe, the characteristics of chemical bonding, electronic band structures and phonon transport properties with high-order anharmonicity were systematically evaluated through first-principles calculations and the self-consistent phonon (SCPH) theory. Our findings reveal that hierarchical chemical bonding, high-order anharmonicity, and frequency renormalization are crucial factors contributing to the ultralow thermal conductivity of TlAgSe. Additionally, the multi-valley characteristics at the band edge, combined with polar optical phonon-dominated carrier scattering, lead to exceptional electrical properties. Consequently, peak ZT of ∼3.06 at a carrier concentration of 4.82 × 10¹⁹ cm⁻³ for p-type doping and ∼2.80 at a carrier concentration of 1.32 × 10¹⁹ cm⁻³ for n-type doping were achieved in TlAgSe at 600 K, highlighting its significant potential for high-performance thermoelectric applications.