Structural and Elastic Properties of Post-Perovskite Related Phases at High PT

高 PT 后钙钛矿相关相的结构和弹性性能

• 批准号: 0510501
• 负责人: John Parise
• 金额: --
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-07-15 至 2009-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0510501&HistoricalAwards=false
• 关键词: Structural; Elastic; Properties; Post; Perovskite

Seismic observations of the D" layer reveal large-scale heterogeneous structures and seismic anisotropy existing at the interface of Earth's mantle and liquid outer core. Recent experiments on MgSiO3 perovskite, the dominant phase in Earth's Lower Mantle, indicate the D" discontinuity might result from a phase transition from perovskite (pv) to a post-perovskite (ppv) of CaIrO3 structure-type. While this discovery by the mineral physics community has led to rapid application to interpretation of the seismic data, there are several open questions concerning the atomic structure and elastic properties of ppv. The structure and elastic properties are data crucial to the testing of theoretical models and to interpretation of the seismic observations. While studies of silicate ppv structure and elasticity is stymied by the extreme conditions required for synthesis, there are recent theoretical predictions and experimental evidence of pv-ppv phase transitions in NaMgF3 starting at as low as P~18 GPa. NaMgF3 is often used as an analogue for the silicate pv phase. Accurate in situ studies of NaMgF3 and of CaIrO3 at high pressures and temperatures offer a way forward for systematic theoretical/experimental studies of the crystal chemistry and elasticity of the ppv structure at ambient and at high PT conditions. Further, the ppv-NaMgF3 can be recovered to ambient conditions when quenched from above 40 GPa at room temperature, allowing accurate studies of crystallography and elasticity at ambient and high PT to address many of the gaps in our knowledge for this new, and until recently, relatively obscure class of materials. Comparisons of the compression mechanism for the pv form of NaNgF3 through the pv-ppv transition would aid in testing the validity of proposed mechanisms in a system that is tractable both theoretically and experimentally. Although challenging theoretically, CaIrO3 itself needs to be reexamined using modern diffraction techniques, since positions of oxygen were only determined graphically in the mid 60's. Because neutrons are more sensitive to the oxygen in the presence of heavy elements such as iridium than are X-rays, a systematic study of this phase at high PT using neuron scattering is required. These studies will be underpinned by theoretical work being carried out in Minnesota on both NaMgF3 and CaIrO3. The diffraction work will be carried out at neutron and synchrotron X-ray facilities with large volume high-pressure devices, where diffraction and ultrasonic data are collected simultaneously, allowing direct correlation of crystal structure and elasticity as pv-NaMgF3 transforms to ppv-NaMgF3. These results will be applicable to the possible pv-ppv transition at the core mantle-boundary.

D”层的地震观测揭示了地幔与液态外核交界面存在大规模非均质结构和地震各向异性。最近对MgSiO3钙钛矿的实验表明，D ‘ ’不连续可能是由钙钛矿（pv）向caro3结构型后钙钛矿（ppv）相变引起的。虽然矿物物理学界的这一发现迅速应用于地震数据的解释，但关于ppv的原子结构和弹性特性仍有几个悬而未决的问题。结构和弹性特性是检验理论模型和解释地震观测结果的关键数据。虽然硅酸盐ppv结构和弹性的研究受到合成所需的极端条件的阻碍，但最近有理论预测和实验证据表明，在低至P~18 GPa的NaMgF3中pv-ppv相变。NaMgF3常被用作硅酸盐pv相的类似物。在高压和高温下对NaMgF3和CaIrO3进行精确的原位研究，为在环境和高PT条件下对ppv结构的晶体化学和弹性进行系统的理论/实验研究提供了一条道路。此外，ppv-NaMgF3在室温下从40 GPa以上淬火后可以恢复到环境条件，从而可以准确地研究室温和高PT下的晶体学和弹性，以解决我们对这种新材料的许多知识空白，直到最近，相对模糊的一类材料。通过pv-ppv转换比较NaNgF3的pv形式的压缩机制将有助于在理论上和实验上都易于处理的系统中测试所提出机制的有效性。虽然理论上具有挑战性，但由于氧的位置在60年代中期才被图形化确定，因此需要使用现代衍射技术重新检查CaIrO3本身。由于中子在重元素（如铱）存在时对氧比x射线更敏感，因此需要使用神经元散射在高PT下对这一阶段进行系统研究。这些研究将以明尼苏达州正在进行的NaMgF3和CaIrO3的理论工作为基础。衍射工作将在具有大体积高压装置的中子和同步加速器x射线设备上进行，同时收集衍射和超声数据，以便在pv-NaMgF3转变为ppv-NaMgF3时直接关联晶体结构和弹性。这些结果将适用于核幔边界可能发生的pv-ppv跃迁。