高压下光伏及多铁储能材料的第一性原理研究

发布时间：2018-12-21 17:48

【摘要】：压力对物质的合成和性质有着巨大影响。高压将使材料的原子间距缩短,改变原子的化学价态,使原子间发生电荷转移,使晶体结构发生变化,从而引发一些特殊的化学反应。因此,高压物理是合成和发现新材料的重要手段。本论文以高压物理为支点,主要包括两个部分。第一部分为高压下的光伏材料方面的研究工作,介绍光伏材料的基本性质和研究分析的方法,并利用第一性原理对I-III-VI族化合物中的AgInS_2进行高压下的理论研究,对于寻找和设计新型光伏半导体材料有着重要的意义。第二部分我们立足于多铁磁电材料的基本理论和应用,并结合目前国内外研究的最新进展,用第一性原理方法研究了高氧压和高压下的多铁材料DyNiO_3的性质并分析研究了其磁电耦合效应的微观物理机制。为设计这种新型的信息存储材料奠定了理论基础。本论文的具体内容如下:首先我们针对目前光伏材料的研究热点I-III-VI族化合物中的AgIn S_2材料,基于第一性原理利用CALYPSO材料结构预测方法进行了高压下的新相结构预测。先前的实验研究发现,CuInS_2在高压9.5GPa左右将转变为立方相结构,并伴随着一些其他性质的改变。然而,对于这种I-III-VI化合物高压下的晶体结构和电子结构性质等理论研究却罕有报道。我们通过理论模拟发现,AgIn S_2的在12.5GPa的压力下结构将从四方相(对称性为I-42d)转变为立方相(对称性为Fd-3m),与实验得出的结论吻合,但是相变压力要大于CuInS_2的相变压力9.5GPa。为了得到体系更加精确的带隙值,我们采用了杂化泛函HSE06方法,计算所得到AgInS_2的立方相带隙为1.2eV左右,较之它的四方相的带隙(2.0eV左右),更为接近理想带隙(1.4eV)。在计算得到声子谱中我们发现布里渊区中没有虚频的存在,说明该结构满足动力学稳定性。同时我们通过计算体系的电子局域函数和电荷密度分析了这种化合物的原子间成键形式。并对常压与高压下不同结构的光学性质进行了计算比较。基于对新材料的设计角度,我们利用密度泛函理论,以高氧压合成的钙钛矿型DyNiO_3为研究对象,分析了GGA+U方法中,U值对该体系性质的影响。系统的研究了该化合物的电子结构、化学键、磁性、铁电性,并分析了其铁电性的来源。我们得到的结果显示,考虑了自旋极化和反铁磁磁结构后高氧压下DyNiO_3体系的对称性由P21/n转变为了P21。计算得出的电子结构性质显示出体系的带隙为0.715eV,为间接带隙化合物。体系中的Ni原子发生了电荷歧化,Ni1原子和Ni2原子的磁矩分别为1.703μB和0.710μB。从体系态密度图的分析中还发现Ni-3d和O-2p态发生了耦合。基于第一性原理,我们还计算了体系的波恩有效电荷和电子局域函数,确定了Ni-O键为离子键。并得到了体系的自发电极化值为6.78μC/cm2,沿着晶格b轴的方向,并指出体系中格点和键中心的电荷有序导致了DyNiO_3中铁电性的形成。最后我们基于第一性原理方法研究了高压下的DyNiO_3的晶体结构、电子结构、磁性和铁电性质。结果表明,在高压下DyNiO_3的晶体结构发生了改变,晶格常数和体积随着压力从0GPa到10GPa的增加而减小。在10GPa的压力下,DyNiO_3的晶体对称性由P21转变为P21/n,并且带隙由高氧压下的0.715eV变为1.25eV,为间接带隙化合物。通过对体系态密度的研究,我们还发现在高压下,Ni1原子位的磁矩不变,而Ni2原子位的磁距在0-10GPa下随着压力的增大而减小,导致了体系磁结构变化。在压力大于6GPa时,Ni2原子位的磁矩消失。这种体系的晶体结构磁结构的变化,消除了体系中的键中心的电荷有序,导致了铁电性消失,从而可以实现用高压对该体系的铁电性的调控。
[Abstract]:The pressure has a great influence on the composition and properties of the substance. The high pressure will shorten the atomic distance of the material, change the chemical valence state of the atom, transfer the charge transfer between the atoms, and cause the crystal structure to change, thus causing some special chemical reactions. Therefore, high-pressure physics is an important means of synthesizing and discovering new materials. The paper takes the high-pressure physics as the fulcrum, which mainly includes two parts. The first part is the research work of the photovoltaic material under high pressure, introduces the basic properties of the photovoltaic material and the method of the research and analysis, and uses the first principle to study the theory of AgInS _ 2 in the compound of the group I-III-VI. It is of great significance to find and design a new type of photovoltaic semiconductor material. The second part is based on the basic theory and application of the multi-ferromagnet electric material, and in combination with the latest development of the research at home and abroad, the properties of the multi-iron material DyNiO _ 3 under high oxygen pressure and high pressure are studied by the first principle method and the micro-physical mechanism of the magnetoelectric coupling effect is analyzed. The theoretical basis is laid for the design of this new information storage material. The specific content of this thesis is as follows: First of all, the new phase structure prediction under high pressure is carried out based on the first principle, based on the first principle, based on the first principle of the AgIn S _ 2 material in the hot spot I-III-VI compound of the present photovoltaic material. Previous experimental studies have found that CuInS _ 2 will transition to a cubic phase structure at a high pressure of 9.5GPa and with some other changes in properties. However, theoretical studies such as the crystal structure and the properties of the electron structure under the high pressure of the I-III-VI compound are rare. The theoretical simulation shows that the structure of AgIn S _ 2 at the pressure of 12. 5GPa will transition from the tetragonal phase (symmetry I-42d) to the cubic phase (symmetry is Fd-3m), which is in agreement with the conclusions of the experiment, but the phase change pressure is higher than the phase change pressure of CuInS _ 2 by 9.5GPa. In order to get a more accurate band gap, we used the hybrid HSE06 method to calculate the cubic phase band gap of AgInS _ 2 as 1. 2eV, which is closer to the ideal band gap (1. 4eV) than the band gap (about 2.0eV) of the tetragonal phase. In the calculation of the acoustic subspectrum, we find that there is no virtual frequency in the Brillouin zone, which indicates that the structure can satisfy the dynamic stability. At the same time, we used the electronic local function and the charge density of the system to analyze the form of the bond between the atoms of the compound. The optical properties of different structures under normal pressure and high pressure are compared. Based on the design angle of the new material, we use the density functional theory, the perovskite type DyNiO _ 3 synthesized with the high oxygen pressure as the research object, and the influence of U value on the property of the system in the GGA + U method is analyzed. The electronic structure, chemical bond, magnetism and ferroelectricity of the compound are studied and the source of its ferroelectric property is analyzed. The results show that the symmetry of the DyNiO _ 3 system under high oxygen pressure after spin-polarization and anti-ferromagnetic structure is changed from P21/ n to P21. The calculated electron structure properties show that the band gap of the system is 0. 715eV, which is an indirect bandgap compound. The Ni atoms in the system have the charge disproportionation. The magnetic moments of the Ni1 and Ni2 atoms are respectively 1. 703. mu.B and 0. 7710. m u.B. The coupling between the Ni-3d and the O-2p states is also found from the analysis of the system state density map. Based on the first principle, we also calculated the effective charge and the electronic local function of the system, and determined that the Ni-O bond is an ionic bond. The spontaneous polarization of the system is 6.78. m u.C/ cm2, along the direction of the lattice b axis, and the charge order of the lattice point and the key center in the system results in the formation of the ferroelectric in DyNiO _ 3. Finally, based on the first principle, the crystal structure, electronic structure, magnetism and ferroelectric property of DyNiO _ 3 under high pressure are studied. The results show that the crystal structure of DyNiO _ 3 has changed under high pressure, and the lattice constant and volume decrease with the increase of the pressure from 0GPa to 10GPa. Under the pressure of 10GPa, the crystal symmetry of DyNiO _ 3 is changed from P21 to P21/ n, and the band gap is changed from 0. 715eV at high oxygen pressure to 1. 25eV, and is an indirect bandgap compound. Through the study of the density of the system state, we have also found that the magnetic moment of the Ni1 atom bit is the same at high pressure, while the magnetic distance of the Ni2 atomic bit decreases with the increase of the pressure at 0-10GPa, resulting in the change of the magnetic structure of the system. When the pressure is greater than 6GPa, the magnetic moment of the Ni2 atomic bit disappears. the change of the magnetic structure of the crystal structure of the system eliminates the charge order of the key center in the system, leads to the disappearance of the ferroelectric property, and can realize the regulation of the ferroelectric property of the system by high voltage.
【学位授予单位】：长春理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O521

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