Theoretical investigation of a three-dimensional phase consisting of binary diamond-like layers

V. A. Greshnyakov ; E. A. Belenkov

Čelâbinskij fiziko-matematičeskij žurnal, Tome 5 (2020) no. 2, pp. 150-160

Résumé

The investigation of the structure and properties of a novel layered carbon phase, consisting of binary diamond-like DL${}_{6}$ layers, was performed by the density functional theory method. As a result of the calculation, it was established that the crystal lattice of this phase belongs to the space group P6${}_{3}$/mmc (No. 194). The packing of diamond-like layers in the DL${}_{6}$ P6${}_{3}$/mmc phase structure is similar to the AB-packing of graphene layers in hexagonal graphite. The hexagonal unit cell has the following parameters: $a$ = $b$ = 0.2738 nm, $c$ = 0.9723 nm, $Z$ = 8. The calculated values of the DL${}_{6}$ P6${}_{3}$/mmc phase density and cohesion energy are 2.529 g/cm${}^{3}$ and 6.65 eV/atom, respectively. The calculation of the electronic structure showed that the new phase should be a semiconductor with an indirect band gap of 1.5 eV. Also, the bulk modulus, which amounted to 261 GPa, was calculated. The maximum Young moduli (784-843 GPa) of the DL${}_{6}$ P6${}_{3}$/mmc phase are observed along crystallographic directions in the plane of the layers, while Young's modulus perpendicular to the layers is an order of magnitude smaller (40 GPa). As a result of molecular-dynamic modeling, it was found that the structure of the new phase should be stable up to 260 K at normal pressure. In addition, the powder X-ray pattern of the DL${}_{6}$ P6${}_{3}$/mmc phase was calculated for its experimental identification in synthesized carbon materials.

Détail

Keywords: diamond, polymorphism, atomic structure, electronic properties, powder X-ray pattern, modeling.