本文選題：自旋相變　切入點(diǎn)：結(jié)構(gòu)相變　出處：《四川師范大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：(Mg,Fe)O方鎂鐵礦和3(Mg,Fe)Si O鈣鈦礦是下地幔中富含的礦物材料,而后鈣鈦礦相(PP v)則是下地幔底部D′區(qū)域中最主要的礦物物質(zhì)。探究這些材料在下地幔壓力環(huán)境下的物理性質(zhì)有其重要地學(xué)價(jià)值。近年來,關(guān)于下地幔礦物輻射熱導(dǎo)率的研究,已成為高壓領(lǐng)域一個(gè)重要的課題。其原因是,這些信息的獲得對(duì)理解下地幔的動(dòng)力學(xué)過程具有重要的意義,為了獲取這些信息,需要計(jì)算得到(Mg,Fe)O方鎂鐵礦和3(Mg,Fe)SiO鈣鈦礦以及后鈣鈦礦在下地幔壓力環(huán)境下的光吸收譜和折射率數(shù)據(jù)。同時(shí),由于礦物的光學(xué)性質(zhì)與其電子結(jié)構(gòu)緊密相關(guān),電子結(jié)構(gòu)信息的獲得將對(duì)理解礦物光學(xué)性質(zhì)變化規(guī)律的微觀機(jī)理有重要貢獻(xiàn)。因此,本文采用第一性原理方法,在常溫和下地幔壓力環(huán)境下,計(jì)算了方鎂鐵礦、鈣鈦礦、后鈣鈦礦理想晶體以及含空位缺陷晶體的電子結(jié)構(gòu)和光學(xué)性質(zhì)。本文主要研究工作和結(jié)論如下:(1)基于第一性原理方法,研究了(Mg_(0.8125),Fe_(0.1875))O方鎂鐵礦理想晶體、含氧離子空位點(diǎn)缺陷晶體在下地幔壓力下的電子結(jié)構(gòu)和光學(xué)性質(zhì)。計(jì)算結(jié)果表明:與晶體場(chǎng)等理論預(yù)測(cè)結(jié)果一致,二價(jià)鐵的電子自旋相變將導(dǎo)致理想晶體帶隙變寬并引起其吸收光譜明顯藍(lán)移,且大約在波數(shù)15000cm-1內(nèi)出現(xiàn)透明現(xiàn)象。然而,缺陷晶體在近紅外光區(qū)的吸收性卻隨鐵雜質(zhì)的自旋態(tài)轉(zhuǎn)變而顯著增強(qiáng)。這意味著,在真實(shí)的摻雜濃度下,僅考慮自旋和壓力因素還不能解釋高壓吸收譜實(shí)驗(yàn)的觀察結(jié)果,壓力誘導(dǎo)的O2-空位點(diǎn)缺陷可能是引起預(yù)測(cè)與實(shí)驗(yàn)結(jié)果出現(xiàn)本質(zhì)差異的重要原因。理想晶體的折射率數(shù)據(jù)表明:鐵自旋相變對(duì)其折射率規(guī)律的影響并不明顯。當(dāng)缺陷晶體發(fā)生自旋相變時(shí),在低能區(qū)域,其折射率緩慢降低;但在高能區(qū)域其折射率卻增大,壓力和波數(shù)對(duì)折射率存在顯著影響。(2)電子結(jié)構(gòu)計(jì)算數(shù)據(jù)表明,空位點(diǎn)缺陷和自旋相變的共同作用下,總態(tài)密度整體藍(lán)移并引起帶隙變寬,價(jià)帶和導(dǎo)帶的峰值強(qiáng)度增加且展開的寬度減小,主峰個(gè)數(shù)降低,這些變化才是引起高壓吸收譜實(shí)驗(yàn)中光吸收性增強(qiáng)的原因。(3)采用第一性原理方法,計(jì)算了(Mg_(0.875),Fe_(0.125))SiO_3鈣鈦礦和(Mg0.9,Fe0.1)SiO_3后鈣鈦礦在高壓下的光學(xué)性質(zhì)和電子結(jié)構(gòu)。計(jì)算數(shù)據(jù)表明:鈣鈦礦的結(jié)構(gòu)相變將導(dǎo)致其吸收性增強(qiáng),證實(shí)了基于實(shí)驗(yàn)數(shù)據(jù)的推斷。而后鈣鈦礦二價(jià)鐵吸收帶的波數(shù)位置與實(shí)驗(yàn)觀測(cè)結(jié)果相近。在后鈣鈦礦相區(qū),壓力將導(dǎo)致吸收帶的強(qiáng)度緩慢增加,但二價(jià)鐵自旋態(tài)的轉(zhuǎn)變對(duì)其吸收譜的影響卻非常微弱。鈣鈦礦的結(jié)構(gòu)相變將導(dǎo)致其折射率升高;在后鈣鈦礦相區(qū),壓力及自旋態(tài)轉(zhuǎn)變對(duì)折射率的影響不明顯。(4)電子結(jié)構(gòu)計(jì)算數(shù)據(jù)表明,不同結(jié)構(gòu)相的態(tài)密度受壓力因素的影響也存在較大差異。在鈣鈦礦相區(qū),態(tài)密度隨壓力的增大而變化緩慢,而后鈣鈦礦相則不同:隨壓力的增大,態(tài)密度峰值強(qiáng)度降低并伴隨發(fā)生顯著的藍(lán)移現(xiàn)象,尖峰的個(gè)數(shù)減少卻表現(xiàn)為寬度增寬,這些變化都與光學(xué)性質(zhì)的變化基本一致。
[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.

【學(xué)位授予單位】：四川師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O469

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