Rattling-like behavior and band convergence induced ultra-low lattice thermal conductivity in MgAl 2 Te 4 monolayer

Inspired by the excellent stability exhibited by experimentally synthesized two-dimensional (2D) MoSi 2 N 4 layered material, the thermal and electronic transport, and thermoelectric (TE) properties of MgAl 2 Te 4 monolayer are systematically investigated using the First-principles calculations and Boltzmann transport theory. The mechanical stability, dynamic stability, and thermal stability (900 K) of the MgAl 2 Te 4 monolayer are demonstrated, respectively. The MgAl 2 Te 4 monolayer exhibits a bandgap of 1.35 eV using the HSE06 functional in combination with spin-orbit coupling (SOC) effect. Band convergence in the valence band is favorable to improve the thermoelectric properties. The rattling thermal damping effect caused by the weak bonding of Mg-Te bonds in MgAl 2 Te 4 monolayer leads to ultra-low lattice thermal conductivity (0.95/0.38 W/(m center dot K)@30 0 K along the x-/ y-direction), which is further demonstrated by the phonon group velocities, phonon relaxation time, Gr & uuml;neisen parameters, and scattering mechanisms. The optimal zT of 3.28 at 900 K is achieved for the p-type MgAl 2 Te 4 monolayer, showing the great promising prospect for the excellent p-type thermoelectric material. Our current work not only reveals the underlying mechanisms responsible for the excellent TE properties, but also elaborates on the promising thermoelectric application of MgAl 2 Te 4 monolayer material at high temperature. (c) 2023 The Authors. Published by Elsevier B.V. on behalf of The Chinese Ceramic Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).