由B、C、N等组成的新型超硬材料的理论研究

发布时间：2018-03-20 17:01

本文选题：硬度　切入点：B-C-N化合物　出处：《西南大学》2017年硕士论文　论文类型：学位论文

【摘要】：超硬材料已经广泛应用于制造磨料,涂料,切割,抛光工具等。现代科学技术的迅速发展,对材料提出了越来越苛刻的性能要求。超硬材料的合成及其性质研究,一直是凝聚态物理和材料科学研究的重点之一。除了金刚石与立方氮化硼(c-BN)以外,BC3、BC5、C3N4、RuO2、OsB2、立方氮碳化硼等材料也日益受到国际材料界的重视。在这些材料的研究中,理论计算已经成为评估或预测材料硬度的有效工具。本论文应用VASP(Vienna Ab-inito Simulation Package)和Materials Studio量化软件包,以密度泛函为主要研究方法对由轻元素B、C、N、O等组成新型材料的弹性性质、硬度、电子性质进行了系统的研究。主要研究内容和结论如下:(1)材料的硬度大于40GPa的材料称之为超硬材料。金刚石是已知的世界上最硬的超硬材料。金刚石具有极高的硬度,但是金刚石容易被氧化,并易于与铁族金属反应,因而限制了它的更广泛的应用。立方氮化硼(c-BN)具有高热、化学稳定性。然而,c-BN的硬度仅在46-66GPa的范围内,这显然远小于金刚石的硬度。鉴于此,本文基于金刚石的结构,构建了1×1×3的超胞,按B、C、N原子比1:4:1取代金刚石超胞结构,构建了C_8B_2N_2晶体结构,经筛选而获得较稳定的t-C_8B_2N_2,运用密度泛函理论下的局域密度近似和广义梯度近似理论对t-C_8B_2N_2晶体结构进行了系统的研究。弹性常数和声子计算,结果表明:t-C_8B_2N_2晶体结构是热力学和动力学稳定的。除此之外,我们使用显微结构模型对极性共价的t-C_8B_2N_2晶体结构的硬度进行了研究。结果表明,t-C_8B_2N_2晶体结构是潜在的新型超硬材料。(2)本文基于立方C6晶体结构,按B、C、N原子比1:1:1取代立方C6晶体结构,构建得到6种稳定的C_2B_2N_2晶体结构,经筛选而获得了较高体弹模量和剪切模量的P3m1-C_2B_2N_2晶体结构。运用密度泛函理论下的局域密度近似(LDA)和广义梯度近似理论(GGA)对P3m1-C_2B_2N_2晶体结构的弹性常数、声子、电子结构、硬度进行了系统的研究。经根据Born-Huang的力学稳定性判据和声子频率计算,结果表明:P3m1-C_2B_2N_2晶体结构是热力学和动力学稳定的。除此之外,我们使用显微结构模型对极性共价的P3m1-C_2B_2N_2晶体结构的硬度进行了研究,计算结果表明,P3m1-C_2B_2N_2晶体结构的硬度(计算硬度67.5GPa)与立方氮化硼的硬度(计算硬度65.4GPa)相媲美。(3)重过渡金属可在化合物中引入高价电子密度以抵抗弹性和塑性变形,因而重过渡金属和轻元素形成的材料家族被认为是潜在的超硬材料。实际上,高硬度的过渡金属氮化物、碳化物和硼化物已经被合成和报道。本文选取了具有较高体弹模量和剪切模量的Os、Pt、Re、Ru、Ir晶体结构,在萤石结构构建了Os、Pt、Re、Ru、Ir等元素的氮化物和氧化物。我们使用第一原理计算萤石(CaF2)结构中Os、Pt、Re、Ru、Ir等元素的碳化物,氮化物和氧化物的体积弹性、剪切模量、杨氏模量、泊松比等弹性性质。筛选得到具有较高体弹模量和剪切模量的ReO2、RuO2晶体结构。经根据Born-Huang的力学稳定性判据和声子频率计算,结果表明:ReO2、RuO2晶体结构是热力学和动力学稳定的。同时ReO2、RuO2晶体结构的弹性性质计算也证明:ReO2、RuO2是潜在的不可压缩的超硬材料。
[Abstract]:Super hard materials have been widely used in the manufacture of abrasive, coating, cutting, polishing tools. The rapid development of modern science and technology, put forward more and more demanding performance of materials. The synthesis and properties of super hard materials, has been one of the focuses of condensed matter physics and material science research. In addition to diamond and cubic boron nitride (c-BN), BC3, BC5, C3N4, RuO2, OsB2, cubic nitrogen boron carbide materials has attracted international attention. The research materials in these materials, the theoretical calculation has become an effective tool to evaluate or predict the hardness of the material. In this paper, the application of VASP (Vienna Ab-inito Simulation Package and Materials Studio) quantitative software package based on density functional as the main research method of the light element B, C, N, O etc. the new elastic properties, the hardness of materials, electronic properties were studied systematically. The main research contents and conclusions Are as follows: (1) hardness greater than 40GPa material called super hard material. The diamond is known to the world's most hard superhard material. Diamond has high hardness, but the diamond is easily oxidized, and is easy to react with iron group metals, which limits its wider application. Cubic boron nitride boron (c-BN) with high thermal, chemical stability. However, the hardness of c-BN only in the range of 46-66GPa, which is obviously far less than the hardness of diamond. In view of this, this paper based on the diamond structure, construction of 1 * 1 * 3 supercell, according to B, C, N atomic ratio of 1:4:1 to replace the diamond cell structure the crystal structure of C_8B_2N_2, construction, through screening and obtain stable t-C_8B_2N_2, by using the local density functional theory approximation and the generalized gradient approximation theory for the research on the crystal structure of t-C_8B_2N_2. The elastic constants and phonon calculations, the results showed that: t-C_8B The crystal structure of _2N_2 is thermodynamically and kinetically stable. In addition, we use the model of the microstructure of t-C_8B_2N_2 crystal structure of polar covalent hardness were studied. The results showed that the crystal structure of t-C_8B_2N_2 is a potential new superhard materials. (2) the cubic crystal structure of C6, based on B, C, N the atomic ratio of 1:1:1 to replace the C6 cubic crystal structure, construct 6 kinds of C_2B_2N_2 stable crystal structure, through screening and obtained the P3m1-C_2B_2N_2 crystal structure of high bulk modulus and shear modulus. By using the local density functional theory approximation (LDA) and the generalized gradient approximation (GGA) theory of elastic constants of P3m1-C_2B_2N_2 crystal structure the phonon, electron structure, hardness was studied. Through calculation, according to the Born-Huang stability criteria and the results show that the phonon frequency of P3m1-C_2B_2N_2 crystal structure and thermodynamic power Study of stability. In addition, we use the model of the microstructure of P3m1-C_2B_2N_2 crystal structure of polar covalent hardness were studied. The calculation results show that the crystal structure of P3m1-C_2B_2N_2 hardness (calculated hardness 67.5GPa) and cubic boron nitride hardness (calculated hardness 65.4GPa) comparable. (3) transition metal can be introduced at high prices the electron density in the compounds to resist the elastic and plastic deformation, so heavy and light transition metal elements form the material family is considered to be the potential superhard materials. In fact, the high hardness of transition metal nitrides, carbides and borides have been synthesized and reported. This paper has high bulk modulus and shear modulus Os Pt, Re, Ru, Ir, crystal structure, the fluorite structure constructed by Os, Pt, Re, Ru, Ir and other elements of the nitride and oxide. We use the first principle calculation of fluorite structure (CaF2) in Os, Pt, Re, Ru, Ir Other elements of the young's modulus of volume elasticity, carbide, nitride and oxide, shear modulus, Poisson's ratio and elastic properties were obtained. With high bulk modulus and shear modulus ReO2, the crystal structure of RuO2. By calculation, according to the Born-Huang stability criteria and the phonon frequency results show that: ReO2, RuO2 and crystal structure of thermodynamics dynamic stability. At the same time ReO2, the elastic properties of the crystal structure of RuO2 ReO2 RuO2, it is proved that calculation is the potential for incompressible super hard materials.

【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ163

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