A DFT study on the transition mechanism of cBN single crystal

ABSTRACT

Using first-principle method based on density functional theory, the surface energy of the low-index surfaces of hexagonal boron nitride (hBN) and cubic boron nitride (cBN) has been studied to reveal the transition mechanism of cBN single crystal under high temperature and high pressure (HTHP). The surface energy of hBN (110) , (100) , (0001) facets and cBN (110), (100) , (111) facets using the GGA is 0.200 eV, 0.427 eV, 0.336 eV and 0.220 eV, 0.430 eV, 0.410 eV under 1800 K and 5.5 GPa, respectively. And the surface energy values of the hBN and cBN facets are 0.221 eV, 0.444 eV, 0.354 eV and 0.250 eV, 0.436 eV, 0.475 eV under 2000 K and 6.0 GPa, respectively. It is found that the lattice plane of (100) in hBN is consecutive with plane (100) of cBN, and relative difference of the two facets in surface energy is only 0.7% and 1.2% under 1800 K, 5.5 GPa and 2000 K, 6.0 GPa, respectively. According to the Modified Thomas-Fermi-Dirac electron theory (TFDC), the direct transition of hBN into cBN can be induced. This indicates that cBN is most likely to be transformed by the hBN under HTHP from the perspective of surface energy of hBN and cBN.

KEYWORDS:

• DFT theory
• surface energy
• cubic boron nitride
• transition mechanism
• high temperature and high pressure

Funding

This work was supported by the National Natural Science Foundation of China under grant No. 51272139.