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

Abstract

The materials with intrinsically lower thermal conductivity and exceptional electrical property are required by high performance thermoelectric materials. The recently synthesized Zintl phase TlAgSe demonstrates lower thermal conductivity; however, it exhibits suboptimal thermoelectric performance. To gain deeper understanding of the mechanism underlying the ultralow lattice thermal conductivity and evaluate the potential of thermoelectric performance, the chemical bonding, electronic band structures and phonon transport properties with high order anharmonicity were systematically evaluated through first-principles calculations and self-consistent phonon (SCP) theory. Our findings reveal that hierarchical chemical bonding, high order anharmonicity, and frequency renormalization are crucial factors contributing to the ultralow thermal conductivity in TlAgSe. Additionally, the multi-valley character at band edge combined with polar optical phonon dominated carrier scattering leads to exceptional electrical properties. Consequently, peak ZT values ~ 3.06 at a carrier concentration of 4.82 * 10^19 cm^-3 for p-type doping and ~ 2.80 at 1.32*10^19 cm^-3 for n-type doping were achieved in TlAgSe at 600 K, highlighting the significant potential of TlAgSe for high-performance thermoelectric applications.