光子晶体光纤中色散管理的理论研究  

Elasticity, hardness and anisotropies of bc-BnCN （n=1, 2, 4）

作　　者：胡萌 陈志谦 李春梅 李凤 王军朋 焦丽娜 

机构地区：西南大学材料与能源学部,重庆400715

出　　处：《中国科学：物理学、力学、天文学》2016年第6期47-59,共13页Scientia Sinica Physica,Mechanica & Astronomica

基　　金：国家重点基础研究发展规划（编号：2009CB724100）和国家自然科学基金（批准号：11221062,11452002）资助项目

摘　　要：本文基于密度泛函理论的第一性原理，分别运用平面波超软赝势和模守恒赝势，选用局域密度近似（LDA）和广义梯度近似（GGA）势场计算了所选3种结构bc-BnCN（n=1，2，4）N弹性和硬度，并分析了它们的弹性各向异性和塑性各向异性各自的差异，结果表明，3种结构在热学和力学上均稳定．能量计算结果显示，B含量最低的bc—BCN形成焓和结合能绝对值最大，结构最稳定，起因于它含有较多能量相对较低的B—N，B—c，c—N键及最少的B—B键．该3种晶体的弹性模量和硬度分析表明，随着B原子数的增多，弹性模量和硬度逐渐减小．根据对普适弹性各向异性指数Au，弹性模量各向异性分数比AB，AG，以及剪切模量各向异性因子A1，A2和A3的计算，分析了3种结构的弹性各向异性，结果表明bc-BCN具有优于c-BN的各向异性性能．通过对这3种结构进行拉伸和剪切模拟得到理想应力．应变曲线，发现其形变过程也呈现出各向异性，指明了不同结构的易屈服面及滑移方向且bc-BCN是3种bc-BnCN（n=1，2，4）中最易合成和最适合应用的超硬材料．Based on the first-principles density functional theory with plane wave ultrasoft and norm-conserving pseudo- potential methods, the elasticity and hardness of the three selected bc-BnCN （n=l, 2, 4） are investigated in details using LDA and GGA potential field. In addition, we pay close attention to their otherness of elastic and plastic anisotropies. The calculated results prove that these three kinds of structures are all stable in thermodynamics. Among these three structures, bc-BCN, which has the maximum absolute values of formation enthalpy and cohesive energy, is the most stable one with the lowest rate of atom B. And the reason why be-BCN is the most resisting structure and has the largest absolute value of energy is that it owns large number of relatively low energy bonds such as B--N, B--C, C--N bonds and the fewest of B--B bond. The analysis of elasticity and hardness results shows that the values of elastic modulus and hardness decrease accordingly with the increasing ratio of atom B in the system. Then in line with the universal elastic anisotropic index Au, percent elastic anisotropy AB and AG, and shear anisotropic factors A1, A2 and A3 of bc-BnCN （n=1, 2, 4）, it is revealed that all of the three structures show different extent of anisotropy. Among these, bc-BCN displays better anisotropic property than c-BN as a whole. Finally, the ideal stress-strain curves of bc-BnCN （n=1, 2, 4） are fitted through the simulation of stepped tensile and shear deformation, and it indicates the anisotropy during deformation process. What＇s more, the matched curves reveal their respective yield surfaces, which are the easiest to slide. Additionally, the most effortless slip directions of different structures are deduced explicitly. In general, bc-BCN is the most easily to synthesize and most suitable for applications among these three compounds.

关 键 词：第一性原理 弹性 硬度 各向异性 

分 类 号：O641.121[理学—物理化学]