Low intrinsic thermal conductivity in sp²-hybrid two-dimensional carbon sheets

Materials with ultralow thermal conductivities are highly desirable for thermal management to capture the enormous amount of waste heat required to generate electricity. In this paper, using first-principles simulations, we investigate the intrinsic phonon transport characteristics of three sp²-hybrid carbon sheets. At room temperature, the lattice thermal conductivity of hybrid Kagome graphene and Kagome graphene is about 445 W m^-1 K^-1 and 42 W m^-1 K^-1, which are merely 5.8% and 1.5% that of graphene, respectively. We attribute these distinct properties to the obvious flat phonon bands in the phonon spectra of the Kagome structure owing to the intrinsic localized vibration ring. To further understand the suppression of the thermal conductivity in the Kagome lattice, we decompose the phonon mode properties. It is found that the low group velocity caused by the flat band and the strong anharmonicity caused by the lattice distortion of the Kagome lattice are the main origins of the obvious suppression of thermal conductivity. The results presented in this work shed light on the lattice thermal conductivity of graphene allotropes with a Kagome lattice and provide a viable way to modulate the thermal conductivity of 2D materials.