Elasticity and structure evolution of carbonates at upper mantle conditions

在这个项目中，我们致力于从常压到中高压和温度(15 GPa和800K)精确和准确地测定主要碳酸盐矿物的全弹性张量，以及它与成分和结构参数的关系，这些参数将在相同的样品上测定。此外，我们还将通过基于密度泛函理论的计算和选定样品的同步X射线热扩散散射(TDS)和非弹性X射线散射(IXS)来补充我们的实验工作。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，是了解地球上碳的深层循环的关键因素。然而，目前关于碳酸盐的弹性性质及其对其结构和组成的依赖的知识仍然很不完整。这一建议的总体目标是了解碳酸盐弹性刚度张量在地幔条件下的p、T、x依赖关系。这一目标将通过布里渊散射、密度泛函理论计算、热扩散散射实验和非弹性X射线散射实验相结合来实现。为了实现这些目标，我们将致力于以下主题：(A)根据需要，通过单晶衍射、红外光谱和拉曼光谱、低温热量计、电子探针和膨胀法对样品进行完整的表征；(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样品和天然样品进行布里渊散射测量。这将使我们能够了解弹性张量对压力、成分和有序态的依赖；(C)通过在电阻加热的钻石顶顶盒中的布里渊散射，将弹性体系扩展到对应于上地幔和高温的压力；(D)利用同步加速器x射线热扩散散射从TDS提取高温弹性刚度系数，并通过高分辨率IXS测量声子；(E)补充基于密度泛函理论的计算的实验研究，以建立非谐性、非线性压力依赖性和有序态的影响，为TDS的测量提供基准。

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.