Thermoelectric and lattice dynamics properties of layered MX (M = Sn, Pb; X = S, Te) compounds

Lead and tin chalcogenides are extensively studied due to their promising thermoelectric (TE) properties. They show an enhancement in the TE efficiency upon the reduction of dimension, which is an important feature in device fabrications. Using density functional theory combined with the semi-classical Boltzmann transport formalism, we studied the structural, electronic, and TE properties of two-dimensional (2D) MX (M = Sn, Pb; X = S, Te) monolayers (MLs). Spin-orbit coupling played a significant role on their electronic structure, particularly for the heavy compounds. Structural optimization followed by phonon transport studies prevailed that the rectangular (gamma-) phase is energetically the most favorable for SnS and SnTe MLs, whereas the square structure is found the most stable for PbS and PbTe MLs. These 2D materials exhibit high Seebeck coefficients (1000-1500 mu V/K) and power factors ((33-77.3) x 10(-4) W m(-1) K-2) along with low lattice thermal conductivities (< 3 Wm(-1) K-1)-these are the essential features of good TE materials. The maximum figure of merits (ZT) of 1.04, 1.46, 1.51, and 1.94 are predicted for n-type SnS, SnTe, PbS, and p-type PbTe MLs, respectively at 700 K, which are higher than their bulk ZT values. Hence, these MLs are promising candidates for TE applications.

Automated summary

Lead and tin chalcogenides have promising thermoelectric properties, with 2D MX monolayers exhibiting high Seebeck coefficients, power factors, and low lattice thermal conductivities, making them potential candidates for thermoelectric applications with higher ZT values than their bulk counterparts.