First-Principles Study Of The Properties Of Cmcm-B₅XO（X=Al、Zr）

Boronous oxide B6O has excellent properties such as high thermal conductivity,high hardness,low density and high chemical inertness,and is widely used in important modern fields such as precision machining of construction machinery,coating of national defense equipment,and paint surface of electronic appliances.In order to improve the defects of brittle fracture of B6O,a new ternary compound Cmcm-B5XO(X=Al,Zr)is proposed.Based on the first principles,the structure,stability,mechanical properties,optoelectronic properties and the influence of doping on the intrinsic mechanism of the material were studied and analyzed.The structure,stability and mechanical properties of Cmcm-B5XO(X=Al,Zr)were investigated by first-principles calculations based on density functional theory.In terms of stability,the calculation results of elastic constants show that the two structures are mechanically stable;there is no imaginary frequency in the phonon dispersion spectrum,indicating that both structures satisfy the dynamic stability.In terms of mechanical properties,Cmcm-B5AlO has larger Young’s modulus and Vickers hardness,so it has higher hardness and better resistance to deformation.The Young’s modulus anisotropy of Cmcm-B5AlO is smaller,and the Young’s modulus anisotropy of Cmcm-B5ZrO is larger.The B/G values of Cmcm-B5XO(X=Al,Zr)are 1.12 and 2.19,respectively,and the Poisson’s ratio is 0.157 and 0.302,respectively.The results show that CmcmB5AlO is a brittle material at 0GPa,while Cmcm-B5ZrO is a plastic material.,indicating that the doping of zirconium element transforms boron suboxide from a brittle material to a plastic material,which significantly improves its brittle fracture defect.In terms of optoelectronic properties,the parameter free density functional model PBE0 hybrid functional was used for calculation.In the electrical properties,the energy band structure diagram shows that there is no forbidden band overlapped between the conduction band and the valence band,indicating that both structures are metal materials with excellent electrical and thermal conductivity.The density of states map shows that the structural stability of Cmcm-B5XO(X=Al,Zr)is closely related to the bonding electron orbitals.In the optical properties,through the analysis of the dielectric constant,absorption spectrum,reflection spectrum,refractive index,electrical conductivity and loss function of Cmcm-B5XO(X=Al,Zr)material,it is found that the two structures have different polarization directions.The absorption coefficients are all above the order of 105cm-1,which indicates that Cmcm-B5XO(X=Al,Zr)has a strong exciton effect.Compared with Cmcm-B5AlO,CmcmB5ZrO has an obvious red-shift phenomenon.The dielectric constant shows that Cmcm-B5ZrO is more likely to obtain energy and undergo electronic transitions,indicating that its electron mobility is higher,and it is easier to obtain response when the material Cmcm-B5ZrO is used in electronic devices.The two new structures proposed in this paper can effectively improve the defects of boron oxide materials that are prone to cracks.At the same time,the performance of the two materials in various aspects has been studied,which is the basis for the follow-up of this new type of superhard material Cmcm-B5XO(X=Al,Zr)research and application in the field of optoelectronics provides a certain reference value.