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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

EarthAfs内部在压缩下的结构变化，例如相变、分解、非晶化或固体反应，已经通过塑性和弹性变形引起的晶格不稳定性进行了讨论。为了阐明地球物理动力学过程，它们的非热结构变化成为更加关键的问题。原位压力引起的结构变化已通过同步加速器辐射进行了研究。链状结构或辉石、橄榄石等层状结构等各向异性结构受到地幔剪切应力的较大影响。非静水条件下产生各向异性晶格变形，这与静水压缩不同。以下实验结果已发表在科学期刊上，并在国际会议或国内科学年会上报告：（1）在动力学低温下，原子迁移率不足以产生热力学稳定相。相变可以通过应力场下的非扩散马氏体转变或小原子位移来实现。 FeGeO3 单斜辉石在静水条件下表现出向高压相（伪钛铁矿）的可逆转变，这是新发现的。然后转变为钛铁矿并进一步转变为钙钛矿结构。这种转变路径是首次发现的。(2)结构变化主要是由外部压力和原子间力之间的维里定理引起的弹性转变引起的。通过使用新设计的金刚石砧和同步加速器辐射，澄清了在高达 50GPa 的高压下 SiO2 石英石的电子密度测量。通过单晶结构分析，证实了成键电子密度随压力的变化。(3)利用SPring-8多砧高压装置，通过时间分辨衍射实验，对石英-柯石英转变动力学进行了研究。分别分析成核和生长，从而给出转变速率和活化能。阐明了成核始于晶面或晶界。(4)研究了水合物的压力诱导非晶化,发现晶格转变的弹性和塑性变形两种不同类型导致了非晶化。(5)MD计算表明这些相变及其动力学过程反映了弹性不稳定性的机制,这是相变过程中原子运动的前兆。一些亚晶格（例如致密区）被保留，而其他亚晶格以随机方式变形。根据 MD 计算得出的作为压力函数的弹性常数 cij 揭示了结构转变过程中的弹性不稳定性。晶格不稳定性可以通过基于 BomÅfs 准则的弹性张量来解释。在某些弹性张量或其组合变为负值的情况下，结构变得不稳定，从而导致相变。(6)结构各向异性按照OstwaldÅfs阶跃规则，使压力下相变动力学中亚稳相发生变化。那么热力学稳定相不仅仅是自然界中发现的候选物。非静水或准静水条件在相变过程中产生亚稳态或中间相。(7)高压EXAFS光谱带来了固体离子的局域结构。通过高温高压研究观察了非哈龙热效应对金金属电对电位的影响。较少的