Elasticity and structure evolution of carbonates at upper mantle conditions

在这个项目中，我们专注于从环境到中等高压和温度（15 GPa和800 K）的主要碳酸盐矿物的全弹性张量的精确和准确的实验测定及其与成分和结构参数的关系，这将在相同的样品上确定。此外，我们将补充我们的实验工作与DFT为基础的计算和同步加速器X射线热漫散射（TDS）和非弹性X射线散射（IXS）选定的样品。了解碳酸盐矿物在岩石圈压力和温度条件下的物理和化学行为是了解地球碳的深层循环的关键因素。然而，目前的知识碳酸盐的弹性性质及其依赖于其结构和组成仍然是远远不够的。这个建议的总体目标是了解的p，T，x-依赖的弹性刚度张量的碳酸盐地幔条件。这一目标将通过布里渊散射，密度泛函理论计算，热漫散射实验和非弹性X射线散射实验的组合来实现。为了实现这些目标，我们将讨论以下主题：（a）通过单晶衍射、红外和拉曼光谱、低温量热法、电子探针和光谱仪进行完整的样品表征;（B）在高达15 GPa的环境条件下，对成分和结构特征良好的合成和天然样品进行布里渊散射测量。这将使我们能够理解弹性张量对压力，成分和有序状态的依赖性;（c）将弹性系统学扩展到对应于 （d）利用同步辐射X射线热漫散射技术从高温TDS中提取弹性刚度系数，并利用高分辨率IXS测量声学声子;（e）通过基于密度泛函理论的计算来补充实验研究，以确定非谐性、非线性压力依赖性的影响，以及排序状态以提供TDS测量的基准。

In this project we focus on the precise and accurate experimental determination of the full elastic tensor of the main carbonate minerals from ambient to moderate high pressures and temperatures (15 GPa and and 800 K) and its relationship with compositional and structural parameters, which will be determined on the same samples. In addition, we will complement our experimental work with DFT-based computations and synchrotron x-ray thermal diffuse scattering (TDS) and inelastic x-ray scattering (IXS) for selected samples. Knowing the physical and chemical behaviour of carbonate minerals at pressure and temperature conditions of the lithosphere is a key factor in understanding the deep cycle of carbon in our planet. However, the current knowledge of the elastic properties of carbonates and their dependence on their structure and composition is still far from being complete. The overall objective of this proposal is to understand the p, T, x-dependence of the elastic stiffness tensor of carbonates up to mantle conditions. This aim will be achieved by a combination of Brillouin scattering, density functional theory calculations, thermal diffuse scattering experiments and inelastic x-ray scattering experiments. In order to achieve the objectives we will address the following topics: (a) perform complete samples characterization by single crystal diffraction, IR- and Raman spectroscopy, low temperature calorimetry, electron microprobe and dilatometry as required; (b) carry out Brillouin scattering measurements of compositionally and structurally well characterised synthetic and natural samples at ambient conditions up to pressures of 15 GPa. This will allow us to understand the dependence of the elastic tensor on pressure, composition and ordering state; (c) extend the elasticity systematics to pressures corresponding to the upper mantle and high temperatures by Brillouin scattering in the resistive-heated diamond anvil cell; (d) use synchrotron x-ray thermal diffuse scattering to extract elastic stiffnes coefficients from TDS for high temperatures and measure acoustic phonons by high resolution IXS; (e) complement the experimental studies by density functional theory based calculations, in order to establish the effect of anharmonicity, non-linear pressure dependencies, and ordering state to provide a benchmark for the TDS measurements.