Lattice Thermal Conductivity Of Beta(12) And Chi(3) Borophene

Borophene allotropes have many unique physical properties due to their polymorphism and similarity between boron and carbon. In this work, based on the density functional theory and phonon Boltzmann transport equation, we investigate the lattice thermal conductivity kappa of both beta(12) and chi(3) borophene. Interestingly, these two allotropes with similar lattice structures have completely different thermal transport properties. beta(12) borophene has almost isotropic kappa around 90 W/(m.K) at 300 K, while kappa of chi(3) borophene is much larger and highly anisotropic. The room temperature kappa of chi(3) borophene along the armchair direction is 512 W/(m.K), which is comparable to that of hexagonal boron nitride but much higher than most of the two-dimensional materials. The physical mechanisms responsible for such distinct thermal transport behavior are discussed based on the spectral phonon analysis. More interestingly, we uncover a unique one-dimensional transport feature of transverse acoustic phonon in chi(3) borophene along the armchair direction, which results in a boost of phonon relaxation time and thus leads to the significant anisotropy and ultrahigh thermal conductivity in chi(3) borophene. Our study suggests that chi(3) borophene may have promising application in heat dissipation, and also provides novel insights for enhancing the thermal transport in two-dimensional systems.