【作者】 谢远亮；

【导师】 邹广田；

【作者基本信息】 吉林大学 ， 凝聚态物理， 2004， 硕士

【摘要】 高压物理研究中，常用红宝石荧光R₁线随压力增加而红移来标定压力。本论文研究高温高压对红宝石荧光R₁线的影响，研究从实验入手，同时做了相关的理论计算。高温高压实验（5GPa＜P＜10GPa，1300K＜T＜2500K）是在激光加热在位高温高压拉曼系统（in situ LHDAC-R）上完成的，理论计算是在运行于高性能工作站上的Materials Studio进行的。 进行红宝石压标的高温高压研究，既是实验上的需求，又有理论上的意义。由于常压下温度对R₁线的影响很大，在1100K时，温度引起R₁线的红移量是195cm^-1，与26.7GPa压力产生的红移量相当。在高温高压条件下用红宝石标压，需要进行研究的问题有：高温时，压腔內的热压不可忽略；高温高压下，电声相互作用发生变化等。因此在高温高压区对红宝石压标进行校正是一个很重要的问题。 红宝石压标目前的理论解释是以晶体场理论为基础的，它使用的模型是[CrO₆]^9-，计算方法是含有经验参数的半经验性算法，一般只把Cr³⁺当作量子体系。由于在高温高压条件下，压腔中红宝石周围的环境很复杂，实验受影响的因素较多，如压机类型、传压介质的选择、垫片是否预压等，要弄清实验中的问题，必须从理论上弄清高温高压对R₁线的影响，而半经验性算法需要从高温高压实验数据中拟和的经验参数，过于依赖实验，无法从根本上解决这个问题。严格的从头算法并不需高温高压实验数据作为计算条件，所以进行从头计算是必要的。 我们实验室在世界上首次把激光加热、金刚石对顶砧（DAC）、拉曼光谱测量等技术结合起来而建立的激光加热在位高温高压拉曼（in situ LHDAC-R）系统，是由激光加热、拉曼光谱测量、光谱测温及加热监控等几个子系统构成的。该系统能实现P＞100GPa，T＞3000K的极端实验条件，我们已经利用它在开展高温高压在位拉曼光谱、合成新材料、寻找物质新相等方面研究。该系统需要用红宝石荧光Rl线在高温高压条件下标定压力，所以本文将研究高温高压对红宝石荧光RI线的影响规律。 本研究中的高温高压实验，选用NaCI作为传压介质和保温材料，为减少压力梯度的影响，红宝石微粒的直径小于10拜m。垫片采用T301不锈钢片，样品腔的直径为100拜m。实验共四组，加热前的压力分别为5.SGPa、6.gGPa、8.OGPa、9.4GPa，压力由红宝石标定。加热过程中，逐渐增大激光器的功率，通过监视器观察加热情况。对加热中燃烧比较稳定的状态进行测量，同时收集红外辐射谱和荧光谱，由红外辐射谱计算出温度。 高温高压条件下测量红宝石荧光Rl线发现:随着温度的升高，高压会抑制温度引起的红移量。对!Cr06}g一用DFT方法计算晶格畸变对Rl线频移的影响，得到:Cr一O键长变短，Rl线会红移;O一Cr一O键角变小，Rl线蓝移。这个结果表明高温高压条件下，Rl线的红移是晶格畸变（Cr一O键长和O一Cr一O键角的变化）以及电声相互作用（声学支和光学支贡献的叠加）等多个因素的综合效应。 以A147CrO72为计算模型，用DFT方法计算出室温常压下的能带，计算值与红宝石的实验值比较相差较大，这是由于计算体系过小引起的。进一步计算杂质Cr3十进入A12O3后对周围晶格的影响，发现Cr3+对其第三近邻原子的影响仍不可忽略。 本文使用的从头算法对传统方法作了重要改进，使用的计算模型考虑了红宝石中Cr3+周围晶格的各向异性，更接近于实际问题，更合理，计算前不需要用实验数据拟和经验参数。 建议用从头算法计算高温高压下红宝石的能带，计算模型选择为A场03 CrO306，这个由510个原子构成的大体系需要的运算量很大，有关计算正在准备进行。更多还原

【Abstract】 The ruby pressure scale, in which pressure is measured on the basis of R1 ruby fluorescence line, is one of the most widely used pressure scale in high pressure study. However, the ruby pressure scale is sensitive to temperature. At atmospheric pressure and 1100K ,the redshift is about 195cm-1,which is equal to the redshift when pressure is 26.7GPa at room temperature.This work mainly studies on the effect of HPHT to the R1 line, including HPHT experiments and some related theory calculations. The HPHT experiments (5GPa < P < 10GPa, 1300K < T < 2500K) are taken on the in situ Laser Heated Diamond Anvil Cell Raman (LHDAC-R) system, and the calculations are taken on Materials Studio running on high performance workstation.The in situ LHDAC-R system is based on double-sided laser heating technique and was constructed in our lab for the first time in the world. Heating the sample in a DAC by introducing laser energy into the DAC,we can perform in intu Raman scattering measurement at megabar pressures and temperatures higher than 3000K. With in situ LHDAC-R system,we have performed in situ HPHT Raman spectroscopy, new materials synthesis, searching for new HPHT state, etc. The error of temperature measurement bv spectral radiometry used on the m situ LHDAC-R system is less than 5%. However, the pressure is not measured in the DAC when laser heating sample as many people did before.In the HPHT experiments of this study, NaCl is chosen as pressure media and insulating material . To avoid the pressure grads ,the size of ruby chip is about 10 m. Gasket is made of T301 stainless steel with a 100 m hole. Four experiments were performed in which the pressures before heating are 5.5,6.9,8.0,9.6GPa . In the former two impressed gaskets are used and inthe latter two not. The power of laser is adjusted while heating for elevating temperature,and the burning state of sample in DAC is watched using monitor. When the sample burns tranquilly,the ruby fluorescence and thermal radiation spectrum are measured.The experiment results tell us that redshift of RI line under HPHT condition is smaller than the one under the same temperature and atmospheric pressure.lt shows that high pressure decreases the redshift of temperature.The redshift of HPHT is not equal to the sum of shift from pressure and temperature respectively.We used [CrO6]9~ as DFT calculation model in order to calculated effect of lattice aberration.lt shows that the redshift of Rj line occurs when the length of Cr-0 bond gets shorter; and blueshift of the R\ line occurs when the bond angle of O-Cr-0 becomes smaller.These results shows that RI line shift at HPHT is the effect of lattice aberration and electron phonon interaction(EPI). The former includes bond stretching of Cr-O and bond angle torsion of 0-Cr-O,while the latter includes acoustic branches and optical branches.More DFT calculations of energy band structures on ALjyCrOyj have been accomplished. The calculation results have a large error ,because the model is too small.The ab initio calculations in this paper are better than old calculations , such as crystal field theory(CFT).The anisotropy which is neglected in CFT calculations is considered in ab initio ones . Moreover, CFT calculations need the empirical parameters fitted from experiments but ab initio calculations not .The calculations in this paper are more reasonable than before .To obtain the HPHT energy band structures of ruby by ab initio calculations, Al2o3CrO3o6 is a more reasonable model. This model is very large and computationally expensive .Some calculations will soon be performed.更多还原