Key Laboratory of High-Temperature and High-Pressure Study of the Earth's Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, Guizhou, China.
University of Chinese Academy of Sciences, 100049, Beijing, China.
Nat Commun. 2023 Mar 24;14(1):1656. doi: 10.1038/s41467-023-37376-1.
Seismological observations suggest that Earth's inner core (IC) is heterogeneous and anisotropic. Increasing seismological observations make the understanding of the mineralogy and mechanism for the complex IC texture extremely challenging, and the driving force for the anisotropic texture remains unclear. Under IC conditions, hydrogen becomes highly diffusive like liquid in the hexagonal-close-packed (hcp) solid Fe lattice, which is known as the superionic state. Here, we reveal that H-ion diffusion in superionic Fe-H alloy is anisotropic with the lowest barrier energy along the c-axis. In the presence of an external electric field, the alignment of the Fe-H lattice with the c-axis pointing to the field direction is energetically favorable. Due to this effect, Fe-H alloys are aligned with the c-axis parallel to the equatorial plane by the diffusion of the north-south dipole geomagnetic field into the inner core. The aligned texture driven by the geomagnetic field presents significant seismic anisotropy, which explains the anisotropic seismic velocities in the IC, suggesting a strong coupling between the IC structure and geomagnetic field.
地震学观测表明，地球的内核（IC）是不均匀和各向异性的。越来越多的地震学观测使得理解复杂的 IC 结构的矿物学和机制极具挑战性，各向异性结构的驱动力仍不清楚。在 IC 条件下，氢在六方密堆积（hcp）固体 Fe 晶格中变得像液体一样高度扩散，这被称为超离子态。在这里，我们揭示了超离子 Fe-H 合金中 H-离子的扩散具有各向异性，沿 c 轴的最低势垒能。在外部电场的存在下，Fe-H 晶格与指向场方向的 c 轴对齐在能量上是有利的。由于这种效应，Fe-H 合金通过南北偶极地磁场的扩散与 c 轴平行于赤道面排列。由地磁场驱动的取向织构呈现出显著的地震各向异性，这解释了 IC 中各向异性地震速度，表明 IC 结构与地磁场之间存在强烈的耦合。
