下地幔压力条件下方镁铁矿、钙钛矿和后钙钛矿的电子结构和光学性质

发布时间：2018-03-08 08:18

本文选题：自旋相变　切入点：结构相变　出处：《四川师范大学》2017年硕士论文　论文类型：学位论文

【摘要】：(Mg,Fe)O方镁铁矿和3(Mg,Fe)Si O钙钛矿是下地幔中富含的矿物材料,而后钙钛矿相(PP v)则是下地幔底部D′区域中最主要的矿物物质。探究这些材料在下地幔压力环境下的物理性质有其重要地学价值。近年来,关于下地幔矿物辐射热导率的研究,已成为高压领域一个重要的课题。其原因是,这些信息的获得对理解下地幔的动力学过程具有重要的意义,为了获取这些信息,需要计算得到(Mg,Fe)O方镁铁矿和3(Mg,Fe)SiO钙钛矿以及后钙钛矿在下地幔压力环境下的光吸收谱和折射率数据。同时,由于矿物的光学性质与其电子结构紧密相关,电子结构信息的获得将对理解矿物光学性质变化规律的微观机理有重要贡献。因此,本文采用第一性原理方法,在常温和下地幔压力环境下,计算了方镁铁矿、钙钛矿、后钙钛矿理想晶体以及含空位缺陷晶体的电子结构和光学性质。本文主要研究工作和结论如下:(1)基于第一性原理方法,研究了(Mg_(0.8125),Fe_(0.1875))O方镁铁矿理想晶体、含氧离子空位点缺陷晶体在下地幔压力下的电子结构和光学性质。计算结果表明:与晶体场等理论预测结果一致,二价铁的电子自旋相变将导致理想晶体带隙变宽并引起其吸收光谱明显蓝移,且大约在波数15000cm-1内出现透明现象。然而,缺陷晶体在近红外光区的吸收性却随铁杂质的自旋态转变而显著增强。这意味着,在真实的掺杂浓度下,仅考虑自旋和压力因素还不能解释高压吸收谱实验的观察结果,压力诱导的O2-空位点缺陷可能是引起预测与实验结果出现本质差异的重要原因。理想晶体的折射率数据表明:铁自旋相变对其折射率规律的影响并不明显。当缺陷晶体发生自旋相变时,在低能区域,其折射率缓慢降低;但在高能区域其折射率却增大,压力和波数对折射率存在显著影响。(2)电子结构计算数据表明,空位点缺陷和自旋相变的共同作用下,总态密度整体蓝移并引起带隙变宽,价带和导带的峰值强度增加且展开的宽度减小,主峰个数降低,这些变化才是引起高压吸收谱实验中光吸收性增强的原因。(3)采用第一性原理方法,计算了(Mg_(0.875),Fe_(0.125))SiO_3钙钛矿和(Mg0.9,Fe0.1)SiO_3后钙钛矿在高压下的光学性质和电子结构。计算数据表明:钙钛矿的结构相变将导致其吸收性增强,证实了基于实验数据的推断。而后钙钛矿二价铁吸收带的波数位置与实验观测结果相近。在后钙钛矿相区,压力将导致吸收带的强度缓慢增加,但二价铁自旋态的转变对其吸收谱的影响却非常微弱。钙钛矿的结构相变将导致其折射率升高;在后钙钛矿相区,压力及自旋态转变对折射率的影响不明显。(4)电子结构计算数据表明,不同结构相的态密度受压力因素的影响也存在较大差异。在钙钛矿相区,态密度随压力的增大而变化缓慢,而后钙钛矿相则不同:随压力的增大,态密度峰值强度降低并伴随发生显著的蓝移现象,尖峰的个数减少却表现为宽度增宽,这些变化都与光学性质的变化基本一致。
[Abstract]:(Mg, Fe) O (Mg, 3 mg iron and Fe Si O) is rich in mineral materials of perovskite in the lower mantle, and the perovskite phase (PP V) is the main mineral material at the bottom of the lower mantle D 'area. In the lower mantle under pressure on the physical properties of these materials have the an important study value. In recent years, research on radiation thermal conductivity of the lower mantle mineral, has become an important subject in high voltage field. The reason is that the process of understanding the dynamics of the lower mantle obtained this information is of great significance, in order to obtain the information needed to calculate the (Mg, Fe) O MAGNESIOFERRITE and 3 (Mg, Fe) SiO perovskite and after the absorption and refraction of perovskite in the lower mantle pressure under the environment of light rate data. At the same time, due to the close related optical properties and electronic structures of minerals, micro electronic structure information obtained will be to understand the changes of optical properties of minerals An important contribution mechanism. Therefore, in this paper, by using the first principle method, at room temperature and the lower mantle pressure environment, magnesia iron ore, the calculation of post perovskite crystal and ideal perovskite, with vacancy crystal electronic structure and optical properties are as follows. The main research work and conclusions: (1) the first principle method based on the study, (Mg_ (0.8125), Fe_ (0.1875)) O MAGNESIOFERRITE ideal crystal, electronic structure and optical properties of oxygen ion vacancy defect in the lower mantle pressure. The calculation results show that the result is consistent with the crystal field theory predicts that electronic spin transition two valent iron will lead to ideal crystal band gap widened and caused the obvious blue shift of absorption spectra, and about wavenumber 15000cm-1 appeared in transparency. However, the defects in the crystal absorption in the infrared region with the spin state of iron impurities change remarkably. This means that, The doping concentration of real, only considering the spin and pressure factors cannot explain the experimental observations of high pressure absorption spectrum, O2- vacancy defects induced by pressure may lead to the prediction and experimental results appear important reasons. The essential difference between the refraction rate of ideal crystal data show that: the effect of iron phase of spin rate regularity of the index of refraction is not when the defect is obvious. Crystal phase of spin, in the low energy region, the refractive index decreased slowly; but in the high-energy region of the refractive index is increased, the pressure and wave number on the refractive index has a significant impact. (2) the electronic structure calculation data show that the interaction of vacancy defects and spin transition, the total density of states the blue shift and cause the gap becomes wider and the peak intensity of the valence band and conduction band increases and the peak width decreases, the number is reduced, these changes is caused by high pressure absorption spectrum of enhanced light absorption experiment in charge The reason. (3) by using the first principle method, the calculation of (Mg_ (0.875), Fe_ (0.125)) SiO_3 (Mg0.9, Fe0.1) perovskite and SiO_3 perovskite under high pressure optical properties and electronic structure. The calculated data show that the perovskite structure transition will lead to its absorption enhancement, confirmed the experimental data the inference based on two valent iron absorption and perovskite. Results and experimental observations with wavenumber positions are similar. In the post perovskite phase, pressure will cause the intensity of absorption band increased slowly, but the change of two valent iron spin on its absorption spectrum influence is very weak. The perovskite structure transition will lead to its refractive index in the post perovskite phase increases; area, pressure and spin state transition has no significant effect on the refractive index. (4) calculated data show that the electronic structure, density of states of different structure affected by stress factors are also quite different. In perovskite phase, the density of States With the increase of pressure, the perovskite phase changes slowly, and then the perovskite phase is different. As the pressure increases, the peak value of density of state decreases, and a significant blue shift occurs. The number of spikes decreases as the width increases. These changes are basically consistent with the change of optical properties.

【学位授予单位】：四川师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O469

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