Modeling of synthesis pathways for diamond-like polycyclobutane phases

Abstract

In this paper, the investigation of possible methods for obtaining two diamond-like polycyclobutane LA3 and LA5 phases was carried out using the density functional theory method. The calculations were performed in the local density approximation and the generalized gradient approximation. It was established that the structures of the polycyclobutane phases can be formed on the basis of layer precursors made of hexagonal L 6 graphene and tetragonal L 4-8 graphene. Tetragonal LA3 phase can be obtained from hexagonal L 6 graphite with AA packing at pressures from 59 to 67 GPa. Another way to obtain this phase is compression of tetragonal L 4-8 graphite AB in the pressure range from 50 to 52 GPa. Orthorhombic LA5 phase can be obtained from orthorhombic L 6 graphite AB and hexagonal L 6 graphite AA in the pressure ranges from 64 to 71 GPa and from 59 to 67 GPa, respectively. Also, this phase can be formed under compression of tetragonal L 4-8 graphite AB when the pressure reaches 46 -50 GPa. The minimum values of the energy barriers separating the structural states corresponding to diamond LA3 and LA5 polymorphs from the states corresponding to different types of graphite are in the range from 0.09 to 0.29 eV / atom, which indicates the stability of these phases under normal conditions. For the experimental identification of diamond-like LA5 phase formed during the compression of orthorhombic graphite along the crystallographic axis [001], a series of the X-ray diffraction patterns of the carbon material in which this phase transition takes place was calculated.