發(fā)布時間：2018-08-18 16:17

【摘要】：探究高壓下氫化物的結(jié)構(gòu)和性質(zhì)是尋找潛在高溫超導(dǎo)材料的重要研究方向之一,也是理解和揭示固態(tài)氫金屬化和超導(dǎo)電性等機(jī)制的重要途徑之一,因此高壓下氫化物的探究是凝聚態(tài)物理領(lǐng)域的前沿和重要課題。在本文中我們選取了第四主族和鑭系元素氫化物,對其高壓下的結(jié)構(gòu)、電子結(jié)構(gòu)及超導(dǎo)電性進(jìn)行了探究,得到了如下重要結(jié)果:1.理論預(yù)測了硅烷高壓下的晶體結(jié)構(gòu),提出兩個新相,其中C2/m結(jié)構(gòu)超導(dǎo)轉(zhuǎn)變溫度達(dá)到100 K。進(jìn)一步探究了該結(jié)構(gòu)高Tc的可能原因,通過理論分析比較影響Tc的參數(shù),得出費(fèi)米面處較高的電子態(tài)密度是導(dǎo)致該結(jié)構(gòu)Tc高的原因。該結(jié)果完善了硅烷高壓下的相圖,對傳統(tǒng)超導(dǎo)體超導(dǎo)機(jī)制的分析及氫的金屬化探究具有重要意義。2.利用結(jié)構(gòu)搜索方法重新尋找了鍺烷的高壓結(jié)構(gòu),通過焓值比較及零點(diǎn)振動能修正,最終得到兩個能量上優(yōu)于已知結(jié)構(gòu)的新的金屬相Ama2和C2/c,超導(dǎo)電性探究得出兩者都具有較高的超導(dǎo)轉(zhuǎn)變溫度。該部分計(jì)算結(jié)果更新了鍺烷的高壓相圖,為理論和實(shí)驗(yàn)進(jìn)一步研究Ge-H體系做了知識儲備。3.通過對Sn-H體系進(jìn)行變組分結(jié)構(gòu)搜索,預(yù)測了一個層狀新結(jié)構(gòu)C2/m Sn H4,此外還提出一個新的穩(wěn)定的組分Sn H8化合物(I-4m2),該結(jié)構(gòu)中所有H都以H2或H3單元的形式存在,進(jìn)一步探究得出H原子的振動模式對該結(jié)構(gòu)超導(dǎo)轉(zhuǎn)變溫度起了重要作用。該部分計(jì)算首次給出Sn-H體系的高壓相圖,為以后Sn-H體系的高壓實(shí)驗(yàn)提供了指導(dǎo)。4.通過對Pb-H體系進(jìn)行變組分結(jié)構(gòu)搜索,首次給出Pb-H體系高壓相圖,發(fā)現(xiàn)探究相對較多的Pb H4化合物在整個研究的壓力區(qū)間都具有較高的焓值,不滿足熱力學(xué)穩(wěn)定性。對該體系穩(wěn)定的組分Pb H8結(jié)構(gòu)的超導(dǎo)電性探究發(fā)現(xiàn)其具有較高的超導(dǎo)臨界溫度。該結(jié)果提出了Pb-H體系高壓下穩(wěn)定的相空間結(jié)構(gòu),對以后該體系性質(zhì)研究做了鋪墊。5.理論預(yù)測了高壓下鑭系稀土元素(Er、Ho)氫化物穩(wěn)定結(jié)構(gòu),首次給出了兩個體系高壓下的相圖,為進(jìn)一步探究該體系可能的超導(dǎo)電性做了鋪墊,且對其他稀土元素氫化物的研究有一定的參考意義。
[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.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：O511.3

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