极端条件下地核中轻元素的研究

The chemical composition and the structure of materials in Earth's core is the key to understand Earth's formation and evolution, interior energy recycling and the generation of Earth's magnetic field. Due to extreme conditions (pressure above ~100 GPa, temperature above ~3000 K) of Earth's core, the unique high pressures and temperatures behaviors of its components have been attracted to lots of studies and become one of the most challenging scientific issues in condensed matter physics. The main component of Earth's core is believed to be iron, and a certain amount of lighter elements (L) with their atomic number smaller than iron (26) is also considered to present in the core. The amount and types of light elements are significant in determining the earth's chemical model, the core anisotropy and geodynamics. Here we propose a study that will undertake a series of investigations of light elements in Earth's core. Diamond anvil cells (DAC) will be combined with microanalysis techniques, to study the partition coefficient of light elements between the core and mantle, phase diagram of Fe-L compounds, and the melting and crystallization behavior of light elements under Earth's core conditions. By developing and applying innovative electromagnetic devices, the behaviors of iron-light elements compounds under controllable magnetic field will be explored, and new results will be provided to understand the behaviors of Fe-L compounds in Earth's core under extreme conditions.

地球内核的化学组成及结构状态是理解地球形成与演化、地球内部能量的产生与释放以及地球磁场的产生与变化的关键问题。由于地球内核处于极端条件(压力大于100 GPa, 温度大于3000 K),研究内核物质在这一超高温高压环境下独特的物理化学变化及也成为凝聚态物理中最具挑战的基础问题之一。内核主要成分为Fe,同时含有一些原子序数较低的轻元素(L)。轻元素的组成与含量对确定地球的化学模型、地核的各向异性以及地球动力学有重要意义。本申请项目将对地核中的轻元素展开一系列研究，利用金刚石压砧（DAC）结合微区分析技术，对轻元素在核幔的分异、轻元素与铁的相图及高压结构、铁轻元素合金在高压下的熔融、结晶等问题进行深入研究。通过设计并使用新的电磁学元件，探索铁轻元素物质在电磁场作用下的高压行为，有望为地球深部研究提供新的数据，更深入地了解铁轻元素在极端条件下的性质。

铁-硫-磷Fe-S-P化合物是陨石及月岩中常见矿物。它们能够在一定的温压条件下形成固溶体。我们用大压机方法合成了高质量的Fe3(S,P)固溶体并研究了其稳定性。我们分别利用同步辐射X射线衍射与X射线发射谱研究了Fe3(S0.5P0.5)样品的压缩性和铁自旋态变化。Fe3(S,P)固体溶液中S的溶解度随压力的增加而增加，合成的纯相Fe3S和Fe3(S0.13P0.87)的最低压强分别是21和8 GPa。Fe3(S0.5P0.5)在18 GPa时，Fe3(S0.5P0.5)的晶胞参数发生不连续变化，对应于固溶体中Fe的自旋由高自旋向低自旋的转变。Fe3(S,P) 固溶体中S的含量随压力的变化也使其成为一种潜在的标型矿物。相关结果发表在《美国矿物学家》。由于氯(Cl)元素具有强亲水性，其在地球化学中有着特殊地位。通过(Mg,Fe)SiO3与盐水及α-FeOOH与盐在约100 GPa，2000 K的高温高压化学反应实验，我们首次合成并解析出了氯化亚铁FeCl2高压立方相。此实验结果表明地球内部Cl循环在含水条件下可以被扩展到下地幔深部。相关结果正在审阅中。