Research On The Structure Prediction And Properties Of Novel Diamond-like Superhard Carbons

Carbon atom has unique sp-,sp²-and sp³-hybrid in order that it can form a wide variety of carbon materials with excellent properties and structures.In the natural state,it often exists in the form of graphite,diamond,and amorphous carbon.Diamond bonded in sp³-hybrid mode is a very representative carbon structure and has excellent properties such as high hardness,wide band gap,strong chemical stability,excellent thermal conductivity,small wave loss and dielectric constant,etc.Based on these excellent properties,diamond has been widely used in petroleum/Natural gas/geothermal energy drilling,electronic/optoelectronic devices,aerospace,precision processing of instrumentation and many other important industries and high-precision fields of the national economy.However,it has always been one of the most challenging scientific problem to find new functional diamond-like structures with excellent performance which is comparable to diamond.Thus,it is of great significance to explore novel diamond-like structures which is comparable to diamond.In this paper,the CALYPSO crystal structure prediction software combined with the first-principles calculation method was used to carry out the prediction and calculation research of the new diamond-like carbon structures.Results were showed as follows:（1）Calculation and analysis of a novel diamond-like carbon structure with super-hard property.Here,we identified a novel super-hard carbon phase with an 16-atom unit cell,termed C16.The stability,mechanical properties,hardness and electronic properties of the structure was calculated based on the density functional theory.The results show that the structure propose here is a direct band gap（4.08 e V）structure with super-hard property（72.6 GPa）.（2）Theoretical research on novel ultrawide band gap carbon structure with super-hard property.A novel structure with an 18-atom trigonal unit cell was proposed here,termed Tri-C18.Based on the first-principles calculation,the kinetics,thermodynamics,mechanical stability,hardness and electronic properties of the obtained Tri-C₁₈ were studied.The results show that Tri-C₁₈ is a stable diamond-like structure with super-hard property（79 GPa）and ultrawide band gap（6.32 e V）,and it may have potential application value in the field of electronic or optoelectronic devices working in the deep ultraviolet region.More importantly,the proposal of Tri-C₁₈ solved the unknown carbon phase found in the chimney soot.（3）Research on porous carbon structure with super-hard property.Eight porous carbon structures with super-hard property have been obtained by prediction.Through theoretical calculations of thermodynamics,kinetics,mechanical properties,and electronic properties,it can be found that five of the eight types of porous structures have super-hard property,and two of them have narrow direct band gap.The obtained super-hard porous structures have great application potential in supercapacitors,photocatalysis and other fields.