Zhang Youjun, Luo Kai, Hou Mingqiang, Driscoll Peter, Salke Nilesh P, Minár Ján, Prakapenka Vitali B, Greenberg Eran, Hemley Russell J, Cohen R E, Lin Jung-Fu
Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China.
Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015.
Proc Natl Acad Sci U S A. 2022 Jan 4;119(1). doi: 10.1073/pnas.2119001119.
Light elements in Earth's core play a key role in driving convection and influencing geodynamics, both of which are crucial to the geodynamo. However, the thermal transport properties of iron alloys at high-pressure and -temperature conditions remain uncertain. Here we investigate the transport properties of solid hexagonal close-packed and liquid Fe-Si alloys with 4.3 and 9.0 wt % Si at high pressure and temperature using laser-heated diamond anvil cell experiments and first-principles molecular dynamics and dynamical mean field theory calculations. In contrast to the case of Fe, Si impurity scattering gradually dominates the total scattering in Fe-Si alloys with increasing Si concentration, leading to temperature independence of the resistivity and less electron-electron contribution to the conductivity in Fe-9Si. Our results show a thermal conductivity of ∼100 to 110 W⋅m⋅K for liquid Fe-9Si near the topmost outer core. If Earth's core consists of a large amount of silicon (e.g., > 4.3 wt %) with such a high thermal conductivity, a subadiabatic heat flow across the core-mantle boundary is likely, leaving a 400- to 500-km-deep thermally stratified layer below the core-mantle boundary, and challenges proposed thermal convection in Fe-Si liquid outer core.
地球核心中的轻元素在驱动对流和影响地球动力学方面发挥着关键作用，而这两者对地球发电机来说都至关重要。然而，铁合金在高压和高温条件下的热输运性质仍不确定。在此，我们利用激光加热金刚石砧室实验以及第一性原理分子动力学和动态平均场理论计算，研究了含4.3 wt%和9.0 wt%硅的固体六方密堆积和液态Fe-Si合金在高压和高温下的输运性质。与铁的情况不同，随着硅浓度的增加，硅杂质散射在Fe-Si合金的总散射中逐渐占主导地位，导致Fe-9Si的电阻率与温度无关，且电子-电子对电导率的贡献减小。我们的结果表明，液态Fe-9Si在最外层地核附近的热导率约为100至110 W⋅m⋅K。如果地核由大量具有如此高导热率的硅（例如，> 4.3 wt%）组成，那么穿过核幔边界的次绝热热流很可能出现，在核幔边界下方留下一个400至500公里深的热分层，这对所提出的Fe-Si液态外核中的热对流提出了挑战。
