First Principle Calculations On B-C-N Compounds With Alternating-stacked BC, CN, BCN Layers And Graphene

The aim of this thesis is to explore new electronic and superhard materials ofBN, CN and BCN, using the first principles method in CASTEP based on thedensity functional theory (DFT). First, the graphite-like alternate layer structureg-C11N4consisted of graphene and triazine was calculated. The metallic g-C11N4isstable on structure and the thermodynamics. Then, five stable structures werediscovered by atomic substitution in triazine of g-C11N4with B atoms, g-BC11N3-2,g-B2C10N3, g-B2C11N2-1, g-B3C11N-2and g-B4C11, in which g-BC11N3-2issemiconductor with gap of0.154eV, and others of them are metallic. There are alsothree stable structures from C atoms substitution, g-C12N3-2, g-C14N-1and g-C15. Allof them are metallic. Meanwhile, the stable structures of all graphite-likecompounds under high pressure have been researched. five metastable diamond-likestructures were obtained, in which d-C11N4, d-BC11N3-2, d-B2C11N2-2andd-B3C11N-2are semiconductor with gap of1.82,2.32,0.796,1.56eV, respectively,and d-C12N3-2are metallic. All of them are superhard materials. The results indicatethat the phase transformation critical pressure is around20GPa from graphite-likecompounds to diamond-like compounds for the five compounds expect C11N4(27.2GPa). In addition, armchair nanotube B4C4(2,2) also was studied. Three B4C4nanotubes with different atom arrangement were proposed. The metallic a-B4C4nanotube with no B-B bond is most stable, in which all atoms play roles to theconductivity.