Comparative investigation of the thermal transport properties of Janus SnSSe and SnS2 monolayers

Abstract

Recently, Janus two-dimensional (2D) materials as a new member of 2D derivatives have been receiving much attention due to their novel properties. In this work, the lattice thermal conductivity κ_L of the Janus SnSSe monolayer is investigated based on first-principles calculations, while that of the SnS₂ monolayer is studied for comparison. It is found the the κ_L values of SnSSe and SnS₂ are 13.3 and 11.0 W m⁻¹ K⁻¹ at room temperature, and acoustic branches dominate their thermal transport. Weaker phonon anharmonicity in SnSSe leads to a slightly higher κ_L, though it has weaker phonon harmonicity. The smaller Grüneisen parameters of TA and LA phonons lower than 1 THz in SnSSe indicate weaker phonon anharmonicity, resulting in a higher κ_L. Finally, the size effect and boundary effect are also investigated, exhibiting that the κ_L can further decrease at the nanoscale. Our work suggests that Janus SnSSe and SnS₂ have a much lower κ_L compared with conventional transition metal dichalcogenides (TMDs) and are potential competitors in the thermoelectric field.