The intrinsically low lattice thermal conductivity of monolayer T-Au6X2 (X = S, Se and Te)

Abstract

Thermal conductivity (κ, which consists of electronic thermal conductivity κ_e and lattice thermal conductivity κ_l), as an essential parameter in thermal management applications, is a critical physical quantity to measure the heat transfer performance of materials. To seek low-κ materials for heat-related applications, such as thermoelectric materials and thermal barrier coatings. In this study, based on a complex cluster design, we report a new class of two-dimensional (2D) transition metal dichalcogenides (TMDs): T-Au₆X₂ (X = S, Se, and Te) with record ultralow κ_l values. At room temperature, the κ_l values of T-Au₆S₂, T-Au₆Se₂, and T-Au₆Te₂ are 0.25 (0.23), 0.30 (0.21), and 0.12 (0.10) W m⁻¹ K⁻¹ along the x-axis (y-axis) direction, respectively, exhibiting good thermal insulation. The ultralow κ_l originates from strong phonon softening and suppression, especially for the phonon with frequency 0–1 THz. In addition, T-Au₆Te₂ holds the lowest group velocity and phonon relaxation time among the three T-Au₆X₂ monolayers. Our study provides an alternative approach for achieving ultralow κ_l through complex cluster replacement. Meanwhile, this new class of TMDs is expected to shine in thermal insulation and thermoelectricity due to their ultralow κ_l values.