碳氢化合物在高压下的物性研究

发布时间：2018-06-10 04:41

本文选题：金刚石对顶砧 + 高压拉曼　；参考：《中国科学技术大学》2016年博士论文

【摘要】：高压己经成为现代科学的一门重要的技术手段,在物理学、化学、材料科学、地球科学等领域中获得广泛的应用和发展。在碳氢化合物中,芳香烃化合物由于具有独特的结构和优异的物理化学性质是近年来人们关注和研究的热点。以芳香烃化合物为基本单元可以制备出许多不同结构的新型功能材料,其结构、性质与苯环单元间的相互作用、成键等因素密切相关。另一方面,压力作为除温度外的另一种条件,对物质的各种性质都存在着不同程度的影响。高压可以有效改变分子间距离,影响其相互作用及成键形式,从而引起物质组成结构(晶体结构、分子结构、原子排列方式)的变化,进而造成材料的能带结构、电子排布、电子轨道结构、电子态密度等性质的一系列变化。因此,在高压下对材料的物性开展研究就显得非常重要。在实验蓬勃发展的同时,相关理论工作也取得了较大的发展。例如基于密度泛函理论计算和模拟,不仅能解释一些实验观测结果,而且还能给出一些有意思的理论预测。本论文采用金刚石对顶砧高压装置,利用高压拉曼光谱实验技术,对几种典型直链碳氢化合物萘和蒽的高压行为进行了系统的研究。同时,结合基于密度泛函理论的第一性原理方法,研究了萘、蒽和二萘嵌苯在高压下的晶格常数、能带结构、能隙和电子态密度随压力的变化关系。主要结果如下：(1)利用高压拉曼光谱实验对多环芳香烃体系中的萘的高压结构和相变情况进行了研究。我们的研究提供了萘分子振动模式随压力的变化关系。结果表明,在压力增加到21.5 GPa时,萘在静水压情形下没有相变发生。随着压力的增加,萘分子的晶格振动峰在整个压力区间发生了比较明显的蓝移,各个振动峰的强度随着压力的增加而缓慢减小。在压力达到11.1 GPa,样品的荧光信号急剧增强,进一步增加压力到17.1 GPa时,只有位于105 cm-1,150 cm-1,195 cm-1,231cm-1,765 cm-1,779 cm-1,1029 cm-1,1402 cm-1,和1458 cm-1能观测到,其他的峰都被样品的荧光信号给覆盖了。结合以前的研究发现,在晶格振动区域,只有位于105 cm-1,150 cm-1,195 cm-1和231 cm-1能被探测到,另外位于105,195,和1000 cm-1处的峰是首次发现。其次,实验数据同时表明随着压力的增加,所有晶格振动频率随压力增加呈现明显减慢的趋势,这可能是因为高压下分子密堆积结构导致材料在高压区域压缩率变小的缘故。(2)对多环芳香烃体系中蒽的高压拉曼光谱实验,研究表明,在压力增加到7.1 GPa时,蒽在静水压情形下没有相变发生。在低于200 cm-1的范围内,光谱中出现四个晶格振动峰可以被观测到,他们分别位于：28 cm-1,34 cm-1,60cm-1,和115 cm-1。值得注意的是在1.4 GPa,晶格振动模式115 cm-1劈裂成144,和150 cm-1。同时,当压力进一步增加到5.5 GPa时,大多数的晶格振动模式被强烈的样品荧光信号给覆盖。另外,在900-1600 cm-’范围内的拉曼峰没有明显的不连续、消失、或分裂。而由于这个区域的拉曼峰是代表碳碳之间的伸缩振动,所以这些峰的行为表明碳碳键在压力6.5 GPa下是十分稳定的。同时也可以说明,晶格振动模式与分子内模相比,呈现出剧烈的变化,主要原因可能是由于在压力的作用下分子间的相互作用的变化强于分子内的相互作用。(3)通过第一性原理计算,结果显示在压力的作用下,蒽分子表现出强烈的各项异性。随着压力的增加,晶格常数a,b和c逐渐下降,而a在压力区间0-30GPa内的变化最大为：Aa=1.65A,而晶格参数b和c随压力的改变分别为：Ab=0.73 A和△c=0.79 A。在相应的压力区间单斜却增加了4.60。在压力的调制作用下,所有C-C共价键和分子间C-C,C-H原子间都随压力急剧减少,在0-30 GPa压力区间内,最短的C-C键的变化量为18 mA；而分子间C-H和C-C原子间距变化范围为618-739 mA,这显示分子间的相互作用要比原子间的相互作用受压力调制的作用要强很多。其中最大的变化发生大约在0—5 GPa区间段,这可能是因为在此压力区间,晶体易于压缩,而随着压力的增加,分子密堆积结构导致材料在高压区域压缩率变小的缘故。萘分子也表现出同样的行为。(4)通过第一性原理计算,萘和蒽的能隙均随着压力的增加而减少,计算结果还表明：萘、蒽和二萘嵌苯的费米面附近的价带和导带的贡献主要来源于C的2p电子态,价带能级的贡献主要来源于H原子的1s电子态。而导带的主要贡献是H原子的1s电子和C原子的2p电子。
[Abstract]:High pressure has become an important technical means of modern science. It has been widely used and developed in the fields of physics, chemistry, material science, earth science and other fields. In hydrocarbons, aromatic hydrocarbons have attracted much attention and research because of their unique structure and excellent physical and chemical properties. A number of new functional materials with different structures can be prepared by the hydrocarbon compounds as the basic units. Their structure, properties are closely related to the interaction between the unit of the benzene ring and the bonding. On the other hand, as another condition except the temperature, the pressure has different effects on the various properties of the material. The high pressure can be effectively changed. Intermolecular distance, affecting the interaction and bonding form, resulting in changes in the structure of the material (crystal structure, molecular structure, atomic arrangement), and a series of changes in the properties of the material band structure, electronic arrangement, electronic orbit structure and electronic density of states. Therefore, the material properties are studied under high pressure. It is very important that the theoretical work has been greatly developed while the experiment is flourishing. For example, the calculation and simulation based on density functional theory can not only explain some experimental observation results, but also give some interesting theoretical predictions. This paper uses diamond to anvil high pressure device and uses high pressure Raman. The high pressure behavior of several typical direct chain hydrocarbons naphthalene and anthracene is systematically studied by spectral technique. At the same time, the lattice constant, energy band structure, energy gap and electron state density with pressure are studied by the first principle method based on density functional theory. The relationship between energy band structure, energy gap and electron density of state with pressure is studied. As follows: (1) the high pressure structure and phase transition of naphthalene in polycyclic aromatic hydrocarbons have been studied by High Pressure Raman spectroscopy. Our study provides the relationship between the vibration mode of naphthalene molecules with the pressure. The results show that there is no phase transition in the hydrostatic pressure when the pressure increases to 21.5 GPa. With the increase of pressure, The crystal lattice vibration peak of naphthalene molecule has a clear blue shift in the whole pressure range, and the intensity of each vibration peak decreases slowly with the increase of pressure. The fluorescence signal of the sample increases sharply at 11.1 GPa and increases the pressure to 17.1 GPa, only at 105 cm-1150 cm-1195 cm-1231cm-1765 cm-1779 cm-1, 1029 cm-11402 cm-1, and 1458 cm-1 can be observed that the other peaks are covered by the fluorescence signals of the sample. Combined with previous studies, it is found that only 105 cm-1150 cm-1195 cm-1 and 231 cm-1 can be detected in the lattice vibrational region, and the peaks at 105195, and 1000 cm-1 are first discovered. Secondly, the experimental data are simultaneously table With the increase of pressure, the vibration frequency of all lattice is obviously slowed down with the increase of pressure. This may be due to the low compression rate of the material in high pressure region. (2) High Pressure Raman spectra of anthracene in the polycyclic aromatic hydrocarbon system, the study showed that anthracene was increased to 7.1 GPa when the pressure was increased. There is no phase transition in the hydrostatic pressure. Within the range of less than 200 cm-1, four lattice vibration peaks are observed in the spectrum, they are located at 28 cm-1,34 cm-1,60cm-1, and 115 cm-1. are worth noticing at 1.4 GPa, the lattice vibration mode 115 cm-1 split into 144, and 150 cm-1., while pressure is further increased to 5.5. At GPa, most of the lattice vibration modes are covered by strong sample fluorescence signals. In addition, the Raman peaks in the 900-1600 cm- 'range are not discontinuous, disappearing, or split. And because the Raman peaks in this region represent the telescopic vibration between carbon and carbon, the behavior of these peaks indicates that carbon carbon bonds are ten under pressure of 6.5 GPa. It is also stable. It can also be explained that the lattice vibration mode has a violent change compared with the intramolecular model. The main reason is that the interaction between molecules is stronger than the intramolecular interaction under the action of pressure. (3) the results of the first principle show that the anthracene molecule is strong under the action of pressure. With the increase of pressure, the lattice constant a, B and C gradually decrease, while the maximum variation of a in the pressure range 0-30GPa is Aa=1.65A, while the lattice parameters B and C are respectively the Ab=0.73 A and delta c=0.79 A. in the corresponding pressure range but increase the value of all the covalent bonds under the pressure modulation. The intermolecular C-C, C-H atoms both decrease sharply with the pressure, and the shortest C-C bond change in the 0-30 GPa pressure range is 18 mA, and the intermolecular C-H and C-C atom spacing is 618-739 mA, which shows that the interaction between the molecules is much stronger than the interaction of the atoms. It occurs about 0 to 5 GPa intervals, which may be because in this pressure range the crystal is easy to compress, and as the pressure increases, the molecular dense structure leads to the smaller compression rate in the high pressure region. The naphthalene molecules also show the same behavior. (4) through the first principle, the gap between naphthalene and anthracene increases with the pressure. The results also show that the contribution of valence band and conduction band near the Fermi surface of naphthalene, anthracene and two naphthalene mainly comes from the 2p electron state of C. The contribution of valence band is mainly from the 1s electron state of H atom. The main contribution of the conduction band is 2p electron of 1s electron of H atom and the C atom of H atom.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O521.21

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