Fe和Fe合金在高温高压下的电热输运性质以及地核的热演化研究

Based on several constraints from seismology, geochemical considerations, and mineral physics, the Earth’s core is composed of Fe-Ni alloy with ~10% of light elements such as Si, S, O, C, and H, which contains a solid inner and a liquid outer core. The core works like a heat engine through heat transfer with a slow cooling and freezing of the liquid Fe core, powering the Earth’s magnetic field and tectonic movements. The heat transfer from the core into the mantle places constraints on the dynamics and thermal evolution of Earth’s core, which could mostly be determined by the transport properties of Fe at relative conditions of the core. However, it has been a challenging task because of the extreme conditions required for these experiments (~136 GPa-360 GPa, ~4000-6000 K), and because obtaining accurate verification of electron-phonon and electron-electron scatterings with theoretical calculations is problematic. The recent studies by different approaches and methods in the experiments and numerical simulations reach different and controversial conclusions at Earth’s core conditions. Here, we will study the transport properties of Fe and Fe-Si alloys at relevant conditions of the Earth’s core through improving and unique experimental method and theoretical calculations. We will figure out the effects of pressure, temperature, and phase transitions on electrical and thermal conductivities of Fe and Fe-Si alloys, and further understand the physics of the transport properties from first principles calculations. The expected results can play an important role to understand the thermal evolution of the Earth’s core, and will have a significant impact in the interdisciplinary field of condensed matter physics and geoscience.

基于地震学、地球化学和矿物物理等数据，地核主要由Fe-Ni和~10%的轻元素（如Si、S、O、C、和H）组成，分为固体内核与液体外核。通过核幔边界的热传递以及地核的长期冷却作用，地核就像一个热引擎为地球的磁场和板块运动提供了能源动力。核幔边界的热传递主要由Fe和Fe合金在高温高压下的电热输运性质决定。由于地核处于超高温高压极端条件（~136 GPa-360 GPa, ~4000-6000 K），实验难以达到并且理论计算也存在很大的不确定性，因而至今该方面研究结果存在很大争议，是地球科学中亟待解决的问题。本项目拟通过高温高压实验和第一性原理计算对Fe和Fe-Si在地核条件下的输运性质进行研究。研究拟了解压力、温度以及轻元素Si对Fe电热导率的影响，并且从物理上了解电子-声子和电子-电子散射对输运性质的作用。该结果将进一步认识地核的热演化，对凝聚态物理和地球科学之间的交叉融合产生积极的意义。

地核主要由铁和一定量的轻元素组成并处于极端高温高压环境（>135 GPa和3500 K）。地核的电热输运性质决定了地核的热传递、冷却速率、地球发电机机制以及熔融地核的结晶与热演化过程。研究地核的动力学和热演化问题需要首先确定Fe和Fe合金在地核温压下的电、热输运性质。然而，由于极端条件物理实验和理论计算的挑战性，关于铁和铁合金在高温高压下的输运性质研究结果非常有限且不一致。本课题基于激光加热金刚石压腔与同步辐射高温高压实验和第一性原理理论计算研究了Fe、Fe-Ni和Fe-Si合金在地核温压下的电阻率和热导率。实验和计算研究结果取得了一致，发现了在高温高下电子-电子散射对铁和铁合金的电、热导率贡献不可忽略，并且在高温高压下传统的Wiedemann-Franz物理定律的适用性被打破。本项目研究结果确定了地核的电、热输运性质，建立了地核的热对流和热演化模型。研究揭示了熔融地核在10-13亿年前开始结晶并形成内地核，并且目前熔融外地核的对流主要由成分对流贡献。地核中如果存在大量Si轻元素，地核顶部可能会形成热分层。