Buckling Hydrogenated Biphenylene Network with Tremendous Stretch Extent and Anomalous Thermal Transport Properties

Hydrogen adsorption is a popular and flexible method to regulate the physical properties of two-dimensional (2D) materials, such as the recently synthesized biphenylene networks. In this study, the mechanical properties and the thermal conductivity (kappa) of a fully hydrogenated biphenylene network (HBPN) under strain were investigated systematically by molecular dynamics (MD) simulation and the wave-packet (WP) propagation method. It was found that HBPN could sustain an unusual strain as large as 28.8 and 34.5% along the zigzag and armchair directions, respectively, which were much larger than the other 2D buckling structures like silicene (about 19.5 and 17%, respectively). Besides, the kappa of HBPN exhibited an anomalous response to the uniaxial tensile strain. Different from its mother structure, like graphene, the kappa of HBPN had an increasing trend with strain, explained here with the phononic density of states (PDOS). The physical mechanism behind this nontrivial thermomechanical behavior of this planar sp(2) hybridized carbon allotrope was related to the following two factors: first, the increase of the number of phonons excited in a low-frequency region, which in general carried more energy, and second, the reduction of the number of higher frequency phonons, thus the weakening of the phonon-surface scattering, both helped increase the thermal conductivity under strain. Moreover, the strain-induced flattening of the structure was another reason to weaken the coupling between phonons with in-plane and curvature vibrational modes. The WP propagation method within MD was also employed to analyze the propagation of phonons inside the HBPN, and group velocities, phonon lifetimes, and mean free paths were obtained. Our research can provide an essential reference for the application of 2D materials in the field of electronic cooling devices and the modification of thermoelectric energy conversion efficiency of materials.