First-principles Study Of The Properties Of Fddd-Zr_xB_3-xC₂

As a typical transition metal carbide,zirconium carbide has been widely used in hard ceramic coatings in extreme environments because of its characteristics of high melting point,high hardness and good electrical conductivity.In order to improve the defect that zirconium carbide material is prone to crack due to high density,two novel orthorhombic structure Fddd-Zr_xB_3-xC₂?x=1,2?structures are proposed by substitution doping.Its stability,mechanical properties,photoelectric properties,and the control mechanism and control law of electronic structure by doping is explored at the atomic scale based on first-principles.By using the GGA-PBE hybrid functional in CASTEP,Fddd-Zr_xB_3-xC₂ is geometrically optimized,and the stability and mechanical properties are studied.The study of stability clarifies the possibility of application in various fields such as the preparation of electronic devices.The results of the mechanical properties investigation showed that the B/G of Zr₂BC₂ and Zr B₂C₂ were significantly increased from 1.5 of the traditional zirconium carbide materials to 3.2 and 6.5,respectively,indicating that the transition from brittle materials to ductile materials was achieved by the doping of boron?B?element.Compared with Zr B₂C₂,the calculation results show that the Young's modulus,bulk modulus,Vickers hardness and shear modulus of Zr₂BC₂ are larger,indicating that Zr₂BC₂ has a stronger hardness.The above two structures are anisotropic,and the ratio of Young's modulus of Zr B₂C₂ in different directions reached 2.63,indicating that the anisotropy of Zr B₂C₂ is obvious.The optical and electrical properties of Fddd-Zr_xB_3-xC₂ were explored using the PBE0 hybrid functional in CASTEP,and the bonding properties of the system were analyzed by electronic local distribution.The Zr-d observed in the PDOS diagram has a large occupation in the conduction band,and the energy band diagram finds that Zr B₂C₂ has the property of semimetal.The optical properties of Fddd-Zr_xB_3-xC₂ were explored by analyzing the absorption coefficient,refraction coefficient,loss function,dielectric constant,reflection coefficient,and conductivity of the two structures.It is found that the absorption coefficients of the two systems in the three polarization directions are above the order of 10⁵cm^-1,indicating that Fddd-Zr_xB_3-xC₂ has a strong exciton effect,and Zr₂BC₂ exhibits a significant red shift compared with Zr B₂C₂.The dielectric constant indicates that Zr₂BC2 can easily obtain energy and then undergo an electronic transition,indicating that the electrons in the system are more mobile.Therefore,when Zr₂BC₂ is applied to electronic devices,the response is easier to obtain.This study proposes two structures that can improve the brittle defects of existing zirconium carbide materials.The performance of the two structures is explained in all aspects,and the optimized composition of such transition metal carbides after doping is revealed.The results of this study provide reference value for the further theoretical,experimental research and application in different fields of the novel hard material Fddd-Zrx B3-x C2.