Collaborative Research: CSEDI--First Principles Calculations and Measurements of Thermal Diffusivity for Application to the Earth's Interior

地球，像任何其他温暖的物体一样，随着时间的推移，通过向周围散发热量而冷却。限制速度的步骤是从较热的内部向地表传递热量，在地表，热量释放表现为火山爆发和地壳和岩石圈板块的运动，这反过来又产生地震。这些近地表现象影响着生物圈和人类活动，因此了解驱动它们的内部热源很重要。内部的冷却是由矿物和岩石的物理性质决定的，其中最重要的是热扩散率和导电性。最近材料科学领域的激光闪光分析（LFA）技术的转移使地质材料的热输运特性得以精确测量。然而，对地球内部的研究需要在实验无法获得的条件下的数据，例如，t2300k和p100gpa。因此，需要一个强大的理论模型来将实验室数据中看到的趋势外推到地球上的条件。模型是可用的，但有严重的缺陷，包括以包含重大和系统性错误的旧数据为基准。这一建议涉及发展一个大大改进的健壮的理论模型，并提供准确的，最先进的热扩散率测量，该模型可以作为基准。该研究对了解岩石圈最外层和金属核-岩石地幔内部边界的传导、内部地幔的循环以及行星体守恒方程非线性反馈的热演化具有重要意义。这项工作不仅将进一步加深我们对行星尺度过程的理解，而且还将探索热输运的微观起源。具体来说，旧的方法，包括与热电偶的物理接触，在298 K附近低估了热扩散系数(D)约25%，并且提供了不正确的D/T符号和大小。许多模型基于错误的概念，即导热系数（* =*CPD，其中为密度，CP为热容）可以完全从热力学性质中获得，热力学性质是静态的，描述了平衡行为，而传输本质上是动态的，涉及振动原子的相互作用，并且发生在非平衡条件下。因此，我们提出了一种基于计算方法的新型模型的构建，该计算方法结合了矿物振动动态相互作用的定量第一性原理计算和微观玻尔兹曼输运理论，以预测稳态非平衡分布和振动能量的变化，并将该模型与简单但相关的系统的激光测量相比较。矿物物理组和固态理论组将并行工作，分别建立可靠的实验和理论数据。最初，研究将集中在计算明显可行的简单系统上：Si， NaCl和MgO，随后扩展到Al2O3和Mg2SiO4。实验工作将集中于将金刚石砧细胞与LFA连接以提高测量精度*

The Earth, like any other warm object, cools with time by shedding its heat to the surroundings. The rate limiting step is transfer of heat from inside the hotter interior to the surface, where heat release is manifest in volcanoes and motions of the crustal and lithospheric plates, which in turn generate earthquakes. These near-surface phenomena impact the biosphere and human endeavors and thus understanding the interior heat source that drives them is important. Cooling of the interior is governed by physical properties of minerals and rocks, foremost of which are thermal diffusivity and conductivity. Recent technology transfer of laser-flash analysis (LFA) from materials science now permits accurate measurement of thermal transport properties of geologic materials. However, studies of the Earth's interior require data at conditions not accessible by experiment, e.g., T 2300 K and P 100 GPa. Therefore, a robust theoretical model is needed to extrapolate the trends seen in the laboratory data to conditions in the Earth. Models are available, but have serious flaws, including being benchmarked against old data that contain significant and systematic errors. This proposal concerns development of a much improved robust theoretical model and providing accurate, state-of-the-art measurements of thermal diffusivity against which this model can be benchmarked. The proposed research is important to understand conduction in the outermost lithosphere layers and in the interior boundary between metal core and rock mantle, mantle circulations in the interior, and thermal evolution of planetary bodies due to nonlinear feedback in conservation equations. This work will further our understanding of not only planetary scale processes, but also probes the microscopic origin of heat transport.Specifically, older methods, involving physical contact with thermocouples, underestimate thermal diffusivity (D) by ~25% near 298 K, and provide incorrect signs and magnitude for D/T. Many models are based on the erroneous notion that thermal conductivity (* =*CPD, where is density and CP is heat capacity) can be obtained entirely from thermodynamic properties, which are static and depict equilibrium behavior, whereas transport by it nature is dynamic, involving interactions of vibrating atoms, and occurs under non-equilibrium conditions. We therefore propose construction of a new type of model based on a computational method that combines the quantitative, first-principles calculation of the dynamic interactions of vibrations in the mineral and microscopic Boltzmann transport theory to predict steady-state non-equilibrium distribution and changes in vibrational energy, and to benchmark this model against laser-flash measurements of simple, but relevant, systems. The mineral physics group and the solid-state theory group will work in parallel to establish reliable experimental and theoretical data, respectively. Initially, the study will focus on simple systems for which calculations are clearly feasible: Si, NaCl, and MgO, subsequently expanding to Al2O3 and Mg2SiO4. Experimental efforts will concentrate on interfacing a diamond anvil cell with the LFA to improve accuracy in measuring *