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Lattice instability and kinetic study of mantle substances in the nonequilibrium process under high-pressure and high stress field

高压高应力场下地幔物质非平衡过程晶格不稳定性及动力学研究

基本信息

批准号：
10304044
负责人：
YAMANAKA Takamitsu
金额：
$ 21.89万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

Structure changes of EarthAfs interiors under compression, such as phase transformation, decomposition, amorphization or solid reactions have been discussed by the lattice instability due to the plastic and elastic deformation. Their athermal structure changes become more crucial problems in order to elucidate geophysical dynamical process. In situ pressure-induced structure changes have been investigated by synchrotron radiation. Anisotropic structures such as chain structure or layered structures like pyroxene and olivine are subjected to a large effect of the shear stress in the mantle. Nonhydrostatic condition gave an anisotropic lattice deformation, which is different from those hydrostatic compression. The following experimental results have been published in science jourals and reported at international conference or domestic science anual meetings :(1) At kinetically low temperatures atomic mobility is not large enough to generate thermodynamically stable phases. The phase tran … More sition is possible by the non-diffusion martensic transformation or small atomic displacement under stress field. FeGeO3 clinopyroxene showed a reversible transformation to high-pressure phase (pseudo ilmenite) under hydrostatic condition, which was newly found. Then it transforms to ilmenite and further perovskite structure. This transition path was firstly found.(2) The structure changes are resulted from the elastic transformation mainly due to the virial theorem between external pressure and interatomic forces. Electron density measurement of SiO2 stishovite under high pressures up to 50GPa was clarified by using the newly devised diamond anvil and synchrotron radiation. Through single-crystal structure analysis the bonding electron density changes with pressure was confirmed.(3) Kinetic study of quartz-coesite transition was carried out by time-resolved diffraction experiment using multianvil high-pressure apparatus at SPring-8. Nucleation and growth were separately analyzed resulting in giving the transition rate and activation energy. It is clarified that the nucleation starts at the crystal surface or grain boundary.(4) Pressure-induced amorfization of hydrates were examined and two different types of the elastic and plastic deformation of lattice transition bring the amorfization.(5) MD calculation suggested that those phase transformations and their dynamical processes reflect the mechanism of elastic instability, which is a precursor atomic movement on the transition process. Some sublattices such as dense zone are preserved and the others are deformed in the random fashion. Elastic constants cij as a function of pressure calculated from MD reveal elastic instability in the course of structure transformation. The lattice instability can be interpreted by elastic tensors based on BomÅfs criterion. Under the condition that some elastic tensors or their combination become negative, structure becomes unstable resulting in the transformation.(6) Structure anisotropy brings the variation of metastable phases in the kinetics of phase transformation under pressure by OstwaldÅfs step rule. Then thermodynamically stable phases are not only candidates found in nature. Nonhydrostatic or quasihydrostatic condition brings metastable or intermediate phases in the proen of phase transition.(7) High-pressure EXAFS spectroscopy brought the local structure of solid ionics. Anharonic thermal effect on the pair potential of gold metal was observed by high-tcmperature and pressure study. Less

从塑性变形和弹性变形引起的晶格不稳定性出发，讨论了压缩条件下EarthAfs内部结构的变化，如相变、分解、非晶化和固相反应等。它们的非热结构变化成为阐明地球物理动力学过程的关键问题。原位压力引起的结构变化已经研究了同步辐射。地幔中的各向异性结构，如链状结构或层状结构，如辉石、橄榄石等，都受到很大的剪应力的影响。非流体静力学条件下，晶格的变形各向异性，这与流体静力学压缩不同。以下实验结果已在科学期刊上发表并在国际会议或国内科学年会上报道：（1）在动力学低温下，原子迁移率不足以产生热力学稳定相。相位转换 ...更多信息通过非扩散马氏体相变或在应力场作用下的小原子位移，使相变成为可能。新发现的FeGeO 3单斜辉石在静水压力条件下发生了高压相（假钛铁矿）的可逆转变，然后转变为钛铁矿，进而形成钙钛矿结构。首次发现了这一过渡路径。(2)结构的变化主要是由弹性变形引起的，这主要是由于外压和原子间力之间的维里定理。利用新设计的金刚石对顶砧和同步辐射技术，对SiO_2中石英石在50 GPa高压下的电子密度进行了测量。通过单晶结构分析，证实了键合电子密度随压力的变化。(3)在SPring-8多砧高压装置上，利用时间分辨衍射实验对石英-柯石英相变进行了动力学研究。分别分析了成核和生长过程，给出了转变速率和活化能。它是澄清，形核开始在晶体表面或晶界。(4)研究了压力诱导水合物的非晶化现象，发现非晶化是由晶格转变的两种不同的弹性和塑性变形引起的。(5)分子动力学计算表明，这些相变及其动力学过程反映了弹性不稳定性机制，弹性不稳定性是相变过程中原子运动的前兆。一些子晶格，如致密区被保留下来，而其他的则以随机的方式变形。由MD计算的弹性常数cij作为压力的函数，揭示了结构转变过程中的弹性不稳定性。晶格不稳定性可以用基于Bom Bounfs判据的弹性张量来解释。在某些弹性张量或它们的组合变为负值的条件下，结构将变得不稳定，从而导致变形。(6)根据Ostwald-Schlafs阶跃规则，结构各向异性引起了加压相变动力学中亚稳相的变化。因此，热力学稳定相不仅是自然界中发现的候选相。非流体静力学或准流体静力学条件在相变过程中产生亚稳相或中间相。(7)高压EXAFS谱带来了固体离子的局域结构。通过高温高压研究，观察到了非谐振热效应对金属金的电子对势的影响。少