The Structure Design And Property Research Of New Materials Based On Carbon And Boron Nitride

Carbon, the sixth element in the periodic stable of elements, can form a variety of structural allotropes due to its ability of sp, sp2 and sp3 hybridization. All kinds of carbon materials play an important role in scientific research and people’s lives.Among various types of carbon materials, metallic carbon allotropes have more fascinating properties. However, there have so far been few progresses in search and synthesis of three dimensional metallic carbon. Here, based on the first-principles calculations, we discover a new stable three dimensional metallic carbon allotrope.This new carbon phase is a mixed sp2-sp3 hybridized bonding network, and it is composed of eighteen atoms per hexagonal primitive cell, so we named it as H18 carbon. We identified the stability of this new carbon phase and evidence its experimental observation by some first-principles calculations. We also elucidated the origin of the metallic feature in H18 carbon. Then, we studied the structural and electronic properties of two new BN compounds Rh6-BN and H18-BN, they are the isoelectronic structures of Rh6 carbon and H18 carbon. And this paper mainly contains two parts, the main contents and results are as follows:In the first part of this paper, we researched the structural and electronic properties of a new stable three dimensional metallic carbon phase H18 carbon. We analyses the total energy as a function of volume per atom, phonon mode, and elastic constants of H18 carbon. We also carried out the ab initio MD simulations with the canonical(NVT) ensemble at different temperatures. All the results verify the stability of H18 carbon. Comparing the simulated XRD spectra of H18 carbon and some other carbon allotropes with the experimental XRD data, we find that H18 carbon may be one of the unidentified carbon phases which were explicitly presented in recent detonation experiments. We also simulated the Raman spectra of H18 carbon and some other carbon allotropes to provide more physical quantities of H18 carbon.The electronic band structures of H18 carbon obtained by PBE and HSE06 methods show that H18 carbon is metallic. To elucidate the origin of the metallic feature in H18 carbon, we calculate the PDOS and the charge density of the partially occupied bands in the energy windows of EF-0.5 to EF+0.5 eV. And we find that the metallicity of H18 carbon is attributed to a large delocalization of the py orbital of the carbon atoms with sp2 hybridization. Be different from the previously proposed 3D metallic carbon allotropes, H18 carbon can not only keep its metallicity at ambient pressure but also can likely maintain its structure at high temperatures. This new novel 3D metallic carbon phase is anticipated to be useful for practical applications such as electronics and mechanics devices.In the second part, we research the isoelectronic structures of Rh6 carbon and H18 carbon: Rh6-BN and H18-BN. We verify their stability by the analysis of total energy, elastic constants and phonon mode. The simulated XRD of Rh6-BN and H18-BN provide more physical properties and will be helpful to identify them in experiment in the future. The calculated electronic band structures of Rh6-BN and H18-BN show that Rh6-BN is a insulator with a indirect band gap of 4.48 eV and H18-BN is a semiconductor with a indirect band gap of 2.31 eV. Our findings broaden our understanding of the BN compounds and will stimulate more research in this field.