Abstract:
Several two-dimensional chalcogenide materials have been in the limelight in the recent past for their promising
thermoelectric properties. It is well established that the thermoelectric performance of materials improves on
reducing the physical dimensionality of the system. Two-dimensional hexagonal chalcogen (S, Se and Te) bearing
compounds of Ga, In and Tl have already been studied extensively in literature. But in those phases, the group-13
non-chalcogen atoms occupy the two inner planes while the chalcogens occupy the two outer planes of the unit
cell. In this work, we have proposed the alternate arrangement in which the chalcogen atoms occupy the two
inner planes while the group-13 atoms occupy the two outer planes of the unit cell. Unprecedentedly, this
alternate arrangement shows much lower thermal conductivity that leads to superior thermoelectric performance. In this work we have studied in details the thermoelectric properties of hexagonal AX (A = Ga, In & Tl, X
= S, Se & Te) monolayers and compare the results having both the atomic arrangements. The very low lattice
thermal conductivity of this new arrangement is due to the outermost valence s-orbital lone pair of the chalcogens which leads to enhanced anharmonicity. We have explained these results from the anti-crossing of the
phonon branches as well. The electronic, dynamical, thermodynamical and elastic properties have also been
studied. We think that these results should have significant impact on the synthesis of high-performance thermoelectric materials based on chalcogenides of gallium, indium and thallium.
