Rattling-like behavior and band convergence induced ultra-low lattice thermal conductivity in MgAl2Te4 monolayer

Inspired by the excellent stability of exhibited by experimentally synthesized two-dimensional (2D) MoSi2N4 layered material, the thermal and electronic transport, and thermoelectric (TE) properties of MgAl2Te4 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 MgAl2Te4 monolayer are demonstrated, respectively. The MgAl2Te4 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 MgTe bonds in MgAl2Te4 monolayer leads to ultra-low lattice thermal conductivity (0.95/0.38 W/mK@300 K along the x-/y-direction), which is further demonstrated by the phonon group velocities, phonon relaxation time, Grüneisen parameters, and scattering mechanisms. The optimal zT of 3.28 at 900 K is achieved for the p-type MgAl2Te4 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 the promising thermoelectric application of MgAl2Te4 monolayer material at high temperature.