Lattice thermal transport in superhard hexagonal diamond and wurtzite boron nitride: A comparative study with cubic diamond and cubic boron nitride

P Chakraborty and GP Xiong and L Cao and Y Wang, CARBON, 139, 85-93 (2018).

DOI: 10.1016/j.carbon.2018.06.025

Hexagonal diamond (h-C) and wurtzite boron nitride (w-BN) are two superhard materials recently identified to be comparable to or even harder than their cubic counterparts, cubic diamond (c-C) and cubic boron nitride (c-BN). To understand the effect of lattice structure on thermal transport in these materials, we conduct first-principles calculations to investigate their harmonic and anharmonic lattice properties. Owing to the strong C-C or B-N bonds, h-C and w-BN are found to have a high lattice thermal conductivity (k(L)) exceeding the overall thermal conductivity of metals, albeit lower than that of their cubic counterparts. By analyzing the phonon band structure and volume of the 3-phonon scattering phase space, we attribute the lower k(L) of the hexagonal phases to their larger volume of 3-phonon scattering phase space than the cubic ones. Moreover, we reveal that a high pressure of 125 GPa leads to a two-to three-fold increase in the k(L) of these materials, because the pressure enlarges the optical-acoustic phonon bandgap and thus reduces the volume of the 3-phonon scattering phase space. This work uncovers the significant effect of lattice structure and pressure on phonon scattering and transport, which is crucial for the application of superhard materials. (C) 2018 Elsevier Ltd. All rights reserved.

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