2000 Fiscal Year Final Research Report Summary
Lattice instability and kinetic study of mantle substances in the nonequilibrium process under high-pressure and high stress field
| Project/Area Number |
10304044
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (A).
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Petrology/Mineralogy/Science of ore deposit
|
|---|
| Research Institution | Osaka University |
|---|
Principal Investigator |
YAMANAKA Takamitsu Gradute School of Science, Osaka Univ. Professor, 大学院・理学研究科, 教授 (30011729)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
NAGAI Takaya Gradute School of Science, Osaka Univ. Research Asociate, 大学院・理学研究科, 助手 (20243131)
OHTAKA Osamu Gradute School of Science, Osaka Univ. Associate Prof., 大学院・理学研究科, 助教授 (40213748)
YOSHIASA Akira Gradute School of Science, Osaka Univ. Associate Prof., 大学院・理学研究科, 助教授 (00191536)
|
|---|
| Project Period (FY) |
1998 – 2000
|
| Keywords | Material science of earth's interiors / structure transition of high pressure and high stress field / metastable and nonequilibrium process / time resolved diffraction pattern measurement / imaging plate X-ray ditector / compression with diamond anvil / solid transfer / dynamics of straction transition |
|---|
| Research Abstract |
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
|
