Collective motion in hcp-Fe at Earth’s inner core conditions

• DOI: 10.1073/pnas.2309952120
• Publication Date: 2023-10-02T19:09:50Z
• Authors: Youjun Zhang; Yong Wang; Yuqian Huang; Junjie Wang; Zhixin Liang; Long Hao; Zhipeng Gao; Jun Li; Qiang Wu; Hong Zhang; Yun Liu; Jian Sun; Jung-Fu Lin
• Keywords: Premelting; Shear modulus; Outer core

Earth’s inner core is predominantly composed of solid iron (Fe) and displays intriguing properties such as strong shear softening an ultrahigh Poisson’s ratio. Insofar, physical mechanisms to explain these features coherently remain highly debated. Here, we have studied longitudinal wave velocities hcp-Fe (hexagonal close-packed iron) at relevant pressure–temperature conditions the using in situ shock experiments machine learning molecular dynamics (MLMD) simulations. Our results demonstrate that velocity along Hugoniot premelting condition, defined T/T m ( T : melting temperature above 0.96, significantly reduced by ~30%, while ratio jumps approximately 0.44. MLMD simulations 230 330 GPa indicate collective motion with fast diffusive atomic migration occurs primarily [100] or [010] crystallographic direction, contributing its elastic enhanced study reveals atoms can diffusively migrate neighboring positions, forming open-loop close-loop clusters conditions. Hcp-Fe thus not ideal previously believed. The behaves like extremely soft ultralow modulus are consistent seismic observations region. findings represents underlying mechanism help unique geodynamic core.