Exploring the ultra-low lattice thermal conductivity of a two-dimensional compound Tl2Se3

Abstract

Two-dimensional (2D) materials have attracted extensive attention in the field of thermoelectric (TE) materials, where heat transport properties play an important role in determining the performance of TE devices. In this paper, we investigate the thermal transport properties of novel 2D Tl2Se3 by means of first-principles approach combined with the Boltzmann transport equation (BTE). The small phonon sound group speed and strong anharmonicity are responsible for an ultra-low kl of 0.28 W/mK of 2D Tl2Se3 at room temperature. Meanwhile, the lattice thermal conductivity gradually decreases with the increase of temperature, indicating its potential value at high-temperature. The anti-bonding orbital filling between the Se-4p and Tl-6p states leads to the weak chemical bonds using the crystal orbital Hamiltonian population (COHP) analysis, which results in low phonon group velocities. Also, due to the strong acoustic-optical coupling in 2D Tl2Se3, the scattering processes of different acoustic modes is further studied to analyze how kl is suppressed. These findings demonstrate that 2D Tl2Se3 has potential applications in TE devices, which will motivate Tl2Se3 based experimental investigations.