Thermal transport in planar sp2-hybridized carbon allotropes: A comparative study of biphenylene network, pentaheptite and graphene

The biphenylene network with periodically arranged four-, six-, and eight-membered rings has been successfully synthesized in very recent experiments. This novel two-dimensional (2D) carbon allotrope has potentials in applications of lithium storage and carbon-based circuitry. Understanding the thermal transport property of biphenylene network is of critical importance for the performance and reliability of its practice applications. To this end, the thermal transport in biphenylene network is comprehensively investigated in this paper with the aid of homogeneous non-equilibrium molecular dynamics (HNEMD), equilibrium molecular dynamics (EMD) and nonequilibrium molecular dynamics (NEMD) simulations. For the sake of comparison, the thermal conductivity of some other 2D sp2-hybridized carbon allotropes such as graphene and pentaheptite is also investigated using the same methods. The thermal conductivities of biphenylene network and pentaheptite predicted from the HNEMD method are, 208.3 W/(mK) and 342.7 W/(mK), respectively, which only equal to one-thirteenth and one-eighth of the value (2812.4 W/(mK)) of graphene. These results obtained from the HNEMD method are found to be in good agreements with the results extracted from EMD and NEMD methods, indicating the reliability of the present results. Based on the spectral heat current decomposition method, the thermal conductivity of all three 2D carbon allotropes is found to be mainly attributed to the flexural phonon mode. Through the analysis of phonon property, mechanical property and electron density distribution, the low thermal conductivity of biphenylene network and pentaheptite smaller than that of graphene is found to stem from the decline in their structural symmetry, which leads to the aggravation of phonon scattering, the decrease of phonon group velocity and the reduction of phonon mean free path.