Phonon thermal transport in beta-NX (X = P, As, Sb) monolayers: A first-principles study of the interplay between harmonic and anharmonic phonon properties

摘要

The investigation of the thermal properties of recently emerged two-dimensional materials is a necessary step towards fulfilling their potential applications in nanoelectronics devices. In this study, the thermal conductivities of beta-NX (X = P, As, Sb) monolayers are investigated using a first-principles density-functional theory approach based on the full solution of the linearized Peierls-Boltzmann transport equation. The results show that the room-temperature thermal conductivities of beta-NP, beta-NAs, and beta-NSb are about 1.1, 5.5, and 34.0 times higher than those of their single-element beta-P, beta-As, and beta-Sb monolayers, respectively. The phonon transport analysis reveals that higher phonon group velocities, as well as higher phonon lifetimes, are responsible for such an enhancement in the lattice thermal conductivities of beta-NX binary compounds compared to their single-element group-VA monolayers. We found that beta-NP has the minimum thermal conductivity among beta-NX monolayers, while it has the minimum average atomic mass, which is in contrast with the common assumption that lower-mass systems exhibit higher thermal conductivities. This work demonstrates the tradeoff between harmonic and anharmonic phonon properties in determining the variation of the thermal conductivity among beta-NX monolayers. The higher anharmonicity in beta-NP is found to be responsible for the lower thermal conductivity of this monolayer.