Search Results (2)

The merging of pore designs is a potential strategy for achieving ultra-low lattice thermal conductivity (κ), for which phonon anharmonicity and size effect are indispensable for discovering novel functional materials in thermal applications. In this study, monolayer holey graphyne (HGY) and boron nitride holey graphyne (BN-HGY) were examined for their phonon thermal transport properties through first-principles calculation and phonon Boltzmann function. HGY exhibits an intrinsic lattice thermal conductivity (κ) of 38.01 W/mK at room temperature, which exceeds BN-HGY’s 24.30 W/mK but is much lower than 3550 W/mK for BTE graphene. The phonon–phonon scattering behavior of BN-HGY is obviously increased compared to HGY due to the enhancement of anharmonicity, which leads to a shorter phonon lifetime and lower κ. Additionally, at room temperature, the representative mean free path (rMFP) of BN-HGY is substantially higher than that of HGY, and the κ of BN-HGY decreases faster at a larger rMFP (within a unit nm). This work will be constructive to further the application of HGY and BN-HGY as thermal management materials. Full article

In a recent experimental accomplishment, a two-dimensional holey graphyne semiconducting nanosheet with unusual annulative π-extension has been fabricated. Motivated by the aforementioned advance, herein we theoretically explore the electronic, dynamical stability, thermal and mechanical properties of carbon (C) and boron nitride (BN) holey graphyne (HGY) monolayers. Density functional theory (DFT) results reveal that while the C-HGY monolayer shows an appealing direct gap of 1.00 (0.50) eV according to the HSE06(PBE) functional, the BNHGY monolayer is an indirect insulator with large band gaps of 5.58 (4.20) eV. Furthermore, the elastic modulus (ultimate tensile strength) values of the single-layer C- and BN-HGY are predicted to be 127(41) and 105(29) GPa, respectively. The phononic and thermal properties are further investigated using machine learning interatomic potentials (MLIPs). The predicted phonon spectra confirm the dynamical stability of these novel nanoporous lattices. The room temperature lattice thermal conductivity of the considered monolayers is estimated to be very close, around 14.0 ± 1.5 W/mK. At room temperature, the C-HGY and BN-HGY monolayers are predicted to yield an ultrahigh negative thermal expansion coefficient, by more than one order of magnitude larger than that of the graphene. The presented results reveal decent stability, anomalously low elastic modulus to tensile strength ratio, ultrahigh negative thermal expansion coefficients and moderate lattice thermal conductivity of the semiconducting C-HGY and insulating BN-HGY monolayers. Full article