从MAX相剥离低维MXene薄层的探索：第一性原理研究

论文总字数：46988字

摘 要

自从石墨被成功剥离为石墨烯以来，关于三维材料转化为二维材料的研究方向一直引人关注。MAX相是一类三元层状化合物的总称，其具有优异的力学稳定性、耐磨性、耐高温性等。Max由三种元素组成，其中M代表早期过渡金属（Sc、Ti、Zr、Hf、V、Nb、Ta或Mo），A代表主要的III和IV族元素。元素周期表（Al、Ga、In、Tl、Si、Ge、Sn、Pb、P、As、Bi、S或Te）。二维层状材料MXene作为MAX相的衍生物，是通过化学刻蚀MAX相的A原子层而获得的一种低维材料。MXene的特点为具有良好的亲水性和导电性，有望运用在储能器件中例如超级电容器等。然而，仍难以确定哪些MAX相可以剥离成MXene，例如即便是稳定的MAX相，也不一定都能制备出MXene。

本文使用基态能量差值法和层间结合能法计算MAX相的剥离能。在此基础上，统计分析了MAX相的结构特点和电子性质，并且描述了MAX相剥离能与基态能量之间的对应关系。用两种方法估算了MAX相的剥离能，发现其趋势相当相似。同时对层间距和剥离能的关系进行研究和总结，发现层间距越小，剥离能越大。最后，计算了电子结构的电子态密度和电荷密度。在综合计算和对比分析的基础上，得出剥离能与MAX相中的M-A键的结合强度成正比，即结合强度越强越强，所需剥离能越大，反之亦然。

因此，本文所得到的剥离能关系可作为进一步理论研究和实验研究的描述。

关键词：第一性原理计算，MAX相及MXene相，范德瓦尔斯修正，剥离能

Abstract

Since graphite was successfully stripped to graphene, discovery of two-dimensional material from their parental three-dimensional material has been rapidly grown and carried out extensively. MAX phase is family of floorboard of the ternary layered compounds, which are showing excellent mechanical stability, wear resistance, high temperature resistant, etc. MAX is composed of three kinds of elements, in which M represents early transition metals(Sc, Ti, Zr, Hf, V, Nb, Ta or Mo), A represents elements of the main group III and IV of the periodic table of elements(Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Bi, S or Te) . Two-dimensional layered material MXene, as the derivative of MAX phases, which is obtained by chemical etching the A layer leaving the low dimensional material. MXene has shown good hydrophilicity and the characteristics of electrical conductivity, which is expected to be used as energy storage, like capacitor. However, it is still difficult to determine which MAX phases can be exfoliated into MXene, e.g. not all MXenes can be prepared, even though the corresponding MAX phases are stable.

In this thesis, the first-principles calculation software VASP is used to calculate the stripping energy of Ti₂MC (M=Al, Ga, In, Pb, Ge, Sn, Tl, Cd, S), MGaC/N (M=Mo, Nb, V) and Ti₃M (M=Al, Ga, Ge, In, Si, Sn) C₂ MAX phases by van der Waals correction, and its related electronic structure and layer spacing properties are investigated.

the ground state energy difference method and the interlayer binding energy method are used to calculate the exfoliation energy. On this basis, the structural characteristics and electronic properties of the MAX phase are statistically analyzed, and the corresponding relationship between the MAX phase stripping energy and the ground state energy is described. The exfoliation energy of MAX phase are estimated by two methods, and it is found that the tendencies were rather similar. Meanwhile, the relationship between the layer spacing and the exfoliation energy was also investigated and summarized. It was found that the smaller the layer spacing is, the greater the stripping energy is. Finally, the electronic states and the charge density of the electronic structure are both calculated. On the basis of comprehensive calculations as well as comparative analysis, it is concluded that the cleavage energy is proportional to the bonding strength of M-A in MAX phase, that is, the stronger the bonding, the greater the stripping energy is required, and vice versa.

Therefore, the exfoliation energy relationship obtained here can be used as a descriptor for further theoretical and experimental investigations.

KEY WORDS: First principles calculation, MAX phases and MXenes, van der Waals interactions, exfoliation energy,

目 录

摘 要 I

Abstract II

第一章 绪论 1

1.1 研究背景与意义 1

1.2 剥离能 5

1.2.1 剥离能定义及研究现状 5

1.2.2 剥离能与层间结合能 8

1.2.3 存在问题 9

1.3 研究目标确定 10

1.4 本文所做工作 12

1.5 本章小结 13

第二章 计算方法简介 13

2.1 第一性原理计算 13

2.2 计算软件包简介 14

2.3 范德瓦尔斯修正 15

2.4 电子结构 15

2.5 本章小结 16

第三章 模型构建与数据分析 16

3.1 模型与结构优化 16

3.2 静态自洽计算 19

3.3 剥离能数据分析 19

3.3.1 211相剥离能数据分析 20

3.3.2 312相剥离能数据分析 23

3.4 层间距数据分析 24

3.5 层间距与剥离能 26

3.6 层间结合能 31

3.7 本章小结 33

第四章 MAX相电子结构与成键特征 35

4.1 态密度和电荷密度 35

4.2 211 MAX相电子结构与成键特征 35

4.3 312 MAX相电子结构与成键特征 39

4.4 单层与多层MAX相 41

4.5 其他MAX相电子结构与成键特征 43

4.6 本章小结 44

第五章 结论与展望 46

5.1 结论 46

5.2 发展前景和未来展望 46

致谢 48

参考文献 49

第一章 绪论

• 1. 研究背景与意义

Barsoum等人^[1]首次在发表的综述中提出一类材料即MAX相，其中M代表的是过渡态金属（Sc、Ti、Zr、Hf、V、Nb、Ta或Mo）,“A”则代表元素周期表Ⅲ、Ⅳ主族的元素（Al、Ga、In、Tl、Si、Ge、Sn、Pb、P、As、Bi、S或Te）,“X”则是碳或者氮，并且n可以从1到4，而目前也有实验和计算数据表面MAX相可以有更高n数的结构，例如514、615和716结构^[2]。MAX相中的元素分布如图1所示。同时，Barsoum等人的综述中还介绍了这类陶瓷材料的一系列优点，它综合了陶瓷材料和金属材料的许多优点，包括低密度、高模量、良好的导电/导热性能、抗热震性、抗损伤容限性以及优良的抗高温氧化性能等。这一系列优异的性能使其具有广阔的应用前景，也因此引起了研究者的广泛关注。

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