| Since fullerene,graphene and carbon nanotubes have been synthesized,it has attracted much attention of researches.In recent years,with the rapidly advancements in computational science,capacity and experimental devices,a variety of carbon materials with different properties have been predicted and synthesized.T-carbon is a carbon material that was predicted in 2011 and synthesized in 2017.As a perfect combination of theoretical prediction and experimentation,it has attracted the attention of a large number of researchers.In this work,based on first principles calculations.The behavior of T-carbon under the influence of temperature and a certain concentration of impurity atoms are explored.In the process of the structure evolution for T-carbon,there emergents a topological phase transition from T-carbon to bct-C16.Inspired by T-carbon and bct-C16 carbon phase,two new carbon phase were designed,named T5-carbon and fco-C6.T5-carbon possess fascinating mechanical and thermal properties.Specially,fco-C6 is confirmed to be ideal Weyl semimetal with only two pairs of Weyl points.Main contents of this paper are summarized as follows:1)Through ab-initio molecular dynamics calculations,it found that T-carbon will transform into a topological nodal ring semimetallic carbon phase bct-C16 under～500 K or doping a certain concentration of transition metal atoms.Then,through the analysis of symmetry and effective k·p model,we confirmed that the semi-metallic properties of the topological nodal ring of bct-C16 are inversion and time reversal symmetries protected.In summary,two schemes are proposed to provide a platform for experimental synthesis of bct-C16 carbon phase.2)Since the carbon tetrahedron in T-carbon reduces its stability,we envisage to reduce the concentration of carbon tetrahedrons in T-carbon.Then,we constructed the crystal structure of T5-carbon by replacing half of the tetrahedra in the T-carbon unit cell with a single carbon atom.The calculation results show that T5-carbon has lower energy and better mechanical and thermal properties than T-carbon,and the electronic structure calculations show that T5-carbon possess very small effective mass of electrons and holes.However,T5-carbon is an indirect wide band gap semiconductor.In order to reduce the band gap of T5-carbon,we replaced the non-tetrahedral carbon atoms with Si and Ti atoms,respectively.It found that the TiC4 transforms into a direct band gap semiconductor,and still has a small effective mass of electrons and holes.Importantly,TiC4 has better visible light absorption capacity than anatase TiO2,which confirms that TiC4 is a good candidate material for photocatalysis.3)Weyl fermion is a kind of fermion that satisfies the Weyl equation.Previous studies have rarely found Weyl fermions in carbon materials.In this article,inspired by T-carbon and bct-C16,we build a spiral carbon network without inversion symmetry and magnetism.Through calculations of its energy band structure,it is found that there are two pairs of intersections between the top of the valence band and the bottom of the conduction band near the Fermi surface,indicating its Weyl fermion characteristics.Then,through the analysis of symmetry and low-energy k·p effective model,it is proved that the Weyl fermions in fco-C6 are protected by time reversal symmetry and double rotational symmetry C2.Importantly,due to the weak spin-orbit coupling of carbon atoms and the only two pairs Weyl fermions in fco-C6,it indicates that fco-C6 is an ideal material for observing Weyl fermions in carbon materials.Figure[26]table[3]reference[159]... |
PDF Full Text Request