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First-principles study of a new superhard material BC_2N

wallpapers News 2021-11-24
First-principles study of a new superhard material BC_2N
Using the Calypso (CALYPSO) crystal structure prediction method based on the particle swarm optimization algorithm, we have discovered a new type of allotrope of BC2N with a tetragonal structure, and the space group is I4/MMM. Utilization based on density functional theory The first-principles calculation method of the new BC2N structure has carried out an in-depth study of the electronic energy band structure, density of states, and elastic properties of the new BC2N structure. The calculation results found that the BC2N structure is dynamically stable and has a large bulk elastic modulus (354.4GPa) and shear modulus (375.5GPa); at the same time, theoretical calculations also show that the structure is a direct bandgap semiconductor with a bandgap width of 2.16eV, and its Vickers hardness value can reach 65.6GPa. Therefore, BC2N is expected to Become a potential new type of superhard material and luminescent material. This work will provide a certain theoretical basis for people to explore new types of superhard materials.
First-principles calculations are used to study the elastic anisotropy properties, stress-strain relationship, hardness, and minimum thermal conductivity properties of the superhard material z-BC2N. The calculated crystal mechanical behavior criterion B/G is 0.87, Poisson's ratio is 0.084, and the universal elastic anisotropy index is 0.09992. The maximum tensile strength in the [100] crystal direction reaches 180 GPa, the maximum shear strength in the (100) [010] strain direction reaches 160 GPa, and the Vickers hardness value is 77.07 GPa. The minimum thermal conductivity based on the Cahill model is 6.811 W/(m·K). The results show that: z-BC2N is a brittle material with good mechanical stability, very high tensile strength, shear strength, the bulk elastic modulus is isotropic, and Young's modulus anisotropy is not large. The minimum thermal conductivity of z-BC2N is lower than that of a diamond.
Based on the first principles, using density functional theory (DFT) under the generalized gradient approximation (GGA) ab initio calculation of plane wave super soft pseudopotential method, starting from the structure of superhard material BeCN2 (I-42d), BCN three is designed. Calculate the elastic constants, phonon spectrum, density of state, theoretical Vickers hardness, and physical property changes under high pressure. The results show that the tetragonal structure BCN ternary compound has three different unit cells, B2CN, BC2N, and BCN2, among which BC2N mechanics Good stability and dynamic stability. The bulk modulus of BC2N is as high as 338 GPa, and there are metal bonds in the crystal structure, which have strong covalent bonds. BC2N has a Vickers hardness of 49.0 GPa, which is a superhard material. The compression rate is low For the superhard material CG-CN, Young's modulus, bulk modulus, shear modulus, and Poisson coefficient all increase with the increase of external pressure, reflecting the rigidity of the structure, resistance to transverse, tangential, and longitudinal deformation. Enhanced.
 

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