The Theoretical Study Of New Superhard Materials Composed Of B,C,N And So On

Superhard materials have been widely used in the manufacture of abrasives,coatings,cutting,polishing tools and so on.The rapid development of modern science and technology,the material made more and more demanding performance requirements.The research on the synthesis and properties of superhard materials has been one of the focuses of condensed matter physics and materials science research.In addition to diamond and cubic boron nitride?c-BN?,BC3,BC5,C3N4,Ru O2,Os B2,cubic boron carbide and other materials are increasingly subject to the international material sector attention.In the study of these materials,theoretical calculations have become an effective tool for assessing or predicting material hardness.In this paper,VASP?Vienna Ab-inito Simulation Package?and Materials Studio quantitative software package,density functional as the main research methods for light elements B,C,N,O and other components of the new material elastic properties,hardness,Conducted a systematic study.The main contents and conclusions are as follows:?1?Material hardness greater than 40 GPa material called superhard material.Diamond is known to be the hardest super hard material in the world.Diamond has a very high hardness,but the diamond is easy to be oxidized and easy to react with iron family metals,thus limiting its wider application.Cubic boron nitride?c-BN?has high heat and chemical stability.However,the hardness of c-BN is only in the range of 46-66 GPa,which is obviously much smaller than that of diamond.In this paper,based on the structure of diamond,a 1×1×3 supercell was constructed.The crystal structure of C₈B₂N₂ was constructed by replacing the diamond supercavity structure with B: C and N atomic ratio of 1: 4: 1.Stable t-C₈B₂N₂,the t-C₈B₂N₂ crystal structure is systematically studied by local density approximation and generalized gradient approximation theory under density functional theory.Elastic constants and phonons.The results show that the crystal structure of t-C₈B₂N₂ is thermodynamically and dynamically stable.In addition,we used the microstructure model to study the hardness of the polar covalent t-C₈B₂N₂crystal structure.The results show that the t-C₈B₂N₂ crystal structure is a potential new superhard material.?2?Based on the cubic C6 crystal structure,six kinds of stable C₂B₂N₂ crystal structures were obtained by replacing the cubic C6 crystal structure with B: C and N atomic ratio of 1: 1: 1,and the bulk modulus and shear The higher modulus P3m1-C₂B₂N₂ crystal structure.The elastic constants,phonons,electronic structures and hardness of the P3m1-C₂B₂N₂ crystal structure were systematically studied by using the local density approximation?LDA?and generalized gradient approximation theory?GGA?under density functional theory.Based on the mechanical stability criterion and phonon frequency of Born-Huang,the results show that the crystal structure of P3m1-C₂B₂N₂ is thermodynamically and dynamically stable.In addition,we used the microstructure model to study the hardness of polarized covalent P3m1-C₂B₂N₂ crystal structure.The calculated results show that the hardness of the P3m1-C₂B₂N₂ crystal structure?calculated hardness of 67.5GPa?is related to cubic boron nitride The hardness?calculated hardness of 65.4GPa?comparable.?3?Heavy transition metals can introduce high valence electron density in the compound to resist elasticity and plastic deformation,and thus heavy metal and light element formation of the material family is considered a potential superhard material.In fact,high hardness transition metal nitrides,carbides and borides have been synthesized and reported.In this paper,Os,Pt,Re,Ru and Ir crystals with high bulk modulus and shear modulus were selected.Nitrides and oxides of Os,Pt,Re,Ru and Ir were constructed in fluorite Things.We calculated the volumetric elasticity,shear modulus,Young's modulus,and Poisson's ratio of carbides,nitrides and oxides of elements such as Os,Pt,Re,Ru and Ir in the fluorite?Ca F2?structure using the first principle Equal elasticity.The Re O2 and Ru O2 crystal structures with high bulk modulus and shear modulus were screened.The results show that the crystal structure of Re O2 and Ru O2 is thermodynamically and dynamically stabilized by Born-Huang's mechanical stability criterion and phonon frequency.At the same time Re O2,Ru O2 crystal structure of the elastic properties of the calculation also proved: Re O2,Ru O2 is a potential incompressible superhard material.