超硬材料BC2N的一种新亚稳结构及其高压物性预测

Prediction on the high-pressure physical properties of a new metastable structure for BC2N compound

硼(B)、碳(C)、氮(N)轻元素因具有较小的原子半径和极强的相互键合能力,其形成的化合物极易形成强共价键和高原子密度的三维网状致密结构,从而成为寻找制备超硬材料的备选体系.本文基于最新研究的机械性能优异的体心四方碳结构模型,构造了一种具有四方对称结构、空间群为I4/mmm的BC2N潜在超硬化合物新结构.利用基于密度泛函理论的第一性原理计算方法,系统地研究了该化合物四方相新结构的热力学、力学和动力学稳定性,表明该四方相BC2N至少在0–60 GPa的压力范围内是力学和动力学稳定的;热力学计算结果显示该结构结合能稍高于BC2N化合物中最稳定的纤锌矿结构,表明新构造的四方结构是BC2N化合物的一个亚稳结构,且其不可压缩性大于其他的硼-碳-氮类化合物如B2CN, BC4N等.在结构稳定性研究的基础上,本文计算了该四方相BC2N化合物在0–60 GPa压力范围内的电子结构,发现其在零压下具有2.16 eV的带宽,为半导体,且随着压力的增加,带隙逐渐加宽;高压弹性特性研究表明BC2N化合物四方结构的体弹性模量、剪切模量、杨氏模量、泊松比、德拜温度、最小热导率和弹性波速均随压力增加呈现出不同的增加趋势且属脆性体质,其弹性各向异性在高压下变得更加明显;同时,大的体弹性模量、大的剪切模量及高维氏硬度表明所构造的空间群为I4/mmm的四方结构是BC2N化合物的一种潜在超硬新结构.

Light elements boron(B),carbon(C)and nitrogen(N)have small atomic radius and strong bonding ability,and the formed compounds are easy to form strong covalent bonds and high atomic density three-dimensional networks structures,makes it an alternative system for the preparation of superhard materials.Based on the newly studied bodycentered tetragonal carbon structure model with excellent mechanical properties,a new structure of BC2N potential superhard compound with tetragonal symmetry structure and space group of I4/mmm was constructed in this paper.Using the first-principles calculation method based on density functional theory,the thermodynamic,mechanical and dynamic stability of the new tetragonal phase structure of the compound was systematically studied.It is shown that the tetragonal phase BC2N is atable in mechanics and dynamics at least in the pressure range of 0–60 GPa.The thermodynamic calculation results show that the structural formation energy is slightly higher than the most stable wurtzite structure in the BC2 N compound,indicating that the newly constructed tetragonal structure is a metastable structure of the BC2N compound,and its incompressibility is greater than other boron-carbon-nitrogen materials such as B2CN and BC4N.Based on the structural stability study,the electronic structure of the tetragonal BC2 N in the pressure range of 0–60 GPa is calculated.It is found to have a bandwidth of 2.16 e Vat zero pressure,which is a semiconductor,and with the increase of pressure,The band gap is gradually widened;the high-pressure elastic properties show that the bulk modulus,shear modulus,Young’s modulus,Poisson’s ratio,Debye temperature,minimum thermal conductivity and elastic wave velocity of the tetragonal structure of BC2N compound are all increased in different increasing tendency with pressure,it shows brittleness and its elastic anisotropy becomes more obvious under high pressure.At the same time,the large bulk modulus,large shear modulus and high Vickers hardness indicate that the constructed tetragonal structure with I4/mmm space group is a potential superhard new structure of BC2N compounds.