高压下第四主族及典型镧系元素氢化物的第一性原理研究

发布时间：2018-08-18 16:17

【摘要】：探究高压下氢化物的结构和性质是寻找潜在高温超导材料的重要研究方向之一,也是理解和揭示固态氢金属化和超导电性等机制的重要途径之一,因此高压下氢化物的探究是凝聚态物理领域的前沿和重要课题。在本文中我们选取了第四主族和镧系元素氢化物,对其高压下的结构、电子结构及超导电性进行了探究,得到了如下重要结果:1.理论预测了硅烷高压下的晶体结构,提出两个新相,其中C2/m结构超导转变温度达到100 K。进一步探究了该结构高Tc的可能原因,通过理论分析比较影响Tc的参数,得出费米面处较高的电子态密度是导致该结构Tc高的原因。该结果完善了硅烷高压下的相图,对传统超导体超导机制的分析及氢的金属化探究具有重要意义。2.利用结构搜索方法重新寻找了锗烷的高压结构,通过焓值比较及零点振动能修正,最终得到两个能量上优于已知结构的新的金属相Ama2和C2/c,超导电性探究得出两者都具有较高的超导转变温度。该部分计算结果更新了锗烷的高压相图,为理论和实验进一步研究Ge-H体系做了知识储备。3.通过对Sn-H体系进行变组分结构搜索,预测了一个层状新结构C2/m Sn H4,此外还提出一个新的稳定的组分Sn H8化合物(I-4m2),该结构中所有H都以H2或H3单元的形式存在,进一步探究得出H原子的振动模式对该结构超导转变温度起了重要作用。该部分计算首次给出Sn-H体系的高压相图,为以后Sn-H体系的高压实验提供了指导。4.通过对Pb-H体系进行变组分结构搜索,首次给出Pb-H体系高压相图,发现探究相对较多的Pb H4化合物在整个研究的压力区间都具有较高的焓值,不满足热力学稳定性。对该体系稳定的组分Pb H8结构的超导电性探究发现其具有较高的超导临界温度。该结果提出了Pb-H体系高压下稳定的相空间结构,对以后该体系性质研究做了铺垫。5.理论预测了高压下镧系稀土元素(Er、Ho)氢化物稳定结构,首次给出了两个体系高压下的相图,为进一步探究该体系可能的超导电性做了铺垫,且对其他稀土元素氢化物的研究有一定的参考意义。
[Abstract]:To explore the structure and properties of hydride at high pressure is one of the important research directions for the potential high temperature superconducting materials. It is also one of the important ways to understand and reveal the mechanism of hydrogen metallization and superconductivity in solid state. Therefore, the exploration of hydride at high pressure is the frontier and important subject in condensed matter physics. In this paper, the structure, electronic structure and superconductivity of the fourth host group and lanthanide hydride at high pressure are investigated, and the following important results are obtained: 1. The crystal structure of silane under high pressure is predicted theoretically and two new phases are proposed in which the superconducting transition temperature of C _ 2 / m structure reaches 100K. The possible causes of the high Tc of the structure are further explored. By theoretical analysis and comparison of the parameters affecting Tc, it is concluded that the high density of electronic states at Fermi surface is the reason for the high Tc of the structure. The results improve the phase diagram of silane under high pressure, which is of great significance to the analysis of superconducting mechanism and the investigation of hydrogen metallization. The high pressure structure of germanium has been rediscovered by structural search method. The comparison of enthalpy and the correction of zero vibration energy have been carried out. Finally, two new metallic phases, Ama2 and C _ 2 / c, whose energy is superior to those of known structures, have been obtained. The superconductivity of these two phases has been investigated and the superconducting transition temperatures have been found to be higher. In this part, the high pressure phase diagram of germanium alkane is updated, and the knowledge reserve is made for the further study of Ge-H system in theory and experiment. A new layered structure C 2 / m Sn H 4 is predicted by searching the variable component structure of Sn-H system. A new stable component Sn H 8 compound (I-4m2) is also proposed, in which all H exists in the form of H 2 or H 3 units. It is found that the vibrational mode of H atom plays an important role in the superconducting transition temperature of the structure. In this part, the high-pressure phase diagram of Sn-H system is given for the first time, which provides guidance for the future high-voltage experiment of Sn-H system. The high pressure phase diagram of Pb-H system was obtained by searching for the variable component structure of Pb-H system. It was found that the relatively large number of PbH4 compounds had higher enthalpy values in the whole pressure range of the study, which did not satisfy the thermodynamic stability. The superconductivity of the stable component Pb H _ 8 is investigated. It is found that the superconducting critical temperature of the system is high. The stable phase space structure of Pb-H system under high pressure is proposed. The stable structure of lanthanide rare earth element (Er-Ho) hydride under high pressure is predicted theoretically, and the phase diagram of two systems at high pressure is given for the first time, which lays the groundwork for further exploring the possible superconductivity of the system. It has some reference significance for the study of other rare earth element hydride.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O511.3

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