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

Abstract

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 ofdimension, 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 roleon their electronic structure, particularly for the heavy compounds. Structural optimization followed by phonon transport studies prevailed that the rectangular (γ-) phaseis 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 µV/K)and power factors ((33–77.3) × 10−4W m−1 K−2) along with low lattice thermal conductivities (<3Wm−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 forn-type SnS, SnTe, PbS, andp-type PbTe MLs, respectively at 700 K, which are higher than their bulkZTvalues. Hence, these MLs are promising candidates for TE applications.