Структура и свойства алмазоподобной фазы, получаемой из тетрагональных графеновых слоев

Abstract

Using the density functional theory method in the generalized gradient approximation in this article, crystal structure and properties of the carbon diamond-like LA10 phase, in which all the atomic positions are crystallographically equivalent, were calculated. The diamond-like LA10 phase structure can be theoretical derived by polymerization of tetragonal L4-8 graphene layers, consisting of fourmembered and eightmembered structural units. The LA10 crystalline phase lattice belongs to a tetragonal crystal system with I41/amd space group symmetry. The body-centered tetragonal unit cell has the following parameters: a = 3.581 Å, c = 8.611 Å, and Z = 16 atoms. Band structure and electron density of states calculations showed that the diamond-like LA10 phase is a wide-gap semiconductor with a band gap of 5.0 eV to 6.1 eV. Furthermore, the LA10 phase should have high strength characteristics: the Knoop hardness is equal to 72.3 GPa, the bulk modulus is 351 GPa. It is also established that the LA10 phase should be stable under normal conditions, as the sublimation energy of this phase is only 6.9% less than the corresponding energy of cubic diamond. The most probable synthetic way to obtain the LA10 phase is a strong static compression of graphite, consisting of tetragonal polymorphic variety graphene, perpendicular to the graphene layers. This diamond-like phase can be experimentally identified by a theoretical powder X-ray diffraction pattern, calculated in this work. The calculated X-ray pattern is quite different from the X-ray patterns cubic diamond and lonsdaleite, but is very close to the X-ray pattern hexagonal graphite.