地球内核超离子态铁合金及其效应

何宇; 孙士川; 李和平

doi:10.11858/gywlxb.20240707

地球内核超离子态铁合金及其效应

doi: 10.11858/gywlxb.20240707

中国科学院地球化学研究所, 中国科学院地球内部物质高温高压重点实验室, 贵州贵阳　550081

基金项目: 国家自然科学基金（42074104）；中国科学院青年交叉团队项目（JCTD-2022-16）

详细信息

作者简介:
何　宇（1985－），男，博士，研究员，主要从事高温高压下地球内部物质性质的计算模拟研究.E-mail：heyu@mail.gyig.ac.cn

中图分类号: O521.2; P313
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- 文章访问数: 142
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出版历程
- 收稿日期: 2024-01-09
- 修回日期: 2024-02-29
- 网络出版日期: 2024-05-10
- 刊出日期: 2024-06-03

Superionic Iron Alloys in Earth’s Inner Core and Their Effects

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

摘要

摘要: 超离子态介于固态与液态之间，被认为广泛存在于地球和行星内部。计算研究发现，在地球内核温度压力条件下，铁-氢、铁-碳、铁-氧合金处于超离子态，表现为氢、碳、氧等元素在固态铁合金中像液体一样快速流动。流动的轻元素导致铁合金软化及地震波速降低，与地球物理观测到的内核密度亏损和低剪切波速的特征一致。内核超离子态铁-氢合金可以与地磁场发生相互作用，在偶极地磁场的驱动下形成定向排列组构，从而解释了内核的各向异性结构成因。内核超离子态铁-轻元素合金的发现更新了人们对内核物态的认知，对掌握地球内核的结构、组成和演化以及内核结构与地球磁场的关系等具有重要意义。
- 超离子态 /
- 地球内核 /
- 铁合金 /
- 各向异性 /
- 第一性原理计算
Abstract: Under the conditions of high temperature and high pressure, a series of materials transform into superionic states, which fall between the solid and liquid states and are widely believed to exist in the interior of Earth and exoplanets. Computational research has found that under the temperature and pressure of the Earth’s inner core, iron-hydrogen, iron-carbon, and iron-oxygen alloys transform to superionic states, manifested as elements such as hydrogen, carbon, and oxygen flowing rapidly like liquids in solid iron alloys. The flowing light elements cause softening of Fe alloys and a decrease in seismic wave velocities, explaining the characteristics of core density deficient and low shear wave velocity observed in geophysics. The superionic iron-hydrogen alloy in the core can interact with the geomagnetic field, forming a lattice preferred orientation fiber driven by a dipole geomagnetic field, explaining the origin of the anisotropic structure in the inner core. The discovery of superionic iron-light-element alloys in the inner core has updated our understanding of the state of the inner core, and is of great significance for understanding the structure, composition, and evolution of Earth’s inner core, as well as the relationship between the inner core structure and the Earth’s magnetic field.
- superionic state /
- Earth’s inner core /
- Fe alloy /
- anisotropic structure /
- first-principles calculations

HTML全文

图 1 常压下H和C在金属中的扩散系数随温度的变化关系^[39]

Figure 1. Diffusion coefficients of H and C in different metals versus temperature at normal pressure^[39]

下载: 全尺寸图片幻灯片

图 2 超离子态和液态下Fe-C、Fe-H、Fe-O合金中Fe和轻元素（C、H、O）的MSD随模拟时间的变化关系

Figure 2. MSD-time curves of light elements (C, H, and O) in superionic and liquid Fe-C, Fe-H and Fe-O alloys

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图 3 260和360 GPa下C、H、O在hcp铁合金中的扩散系数随温度的变化关系

Figure 3. Diffusion coefficients of C, H, and O in hcp-Fe versus temperature at 260 and 360 GPa

下载: 全尺寸图片幻灯片

图 4 360 GPa下超离子态hcp相FeH_0.25、FeO_0.0625和FeC_0.0625的纵波波速（v_P）和横波波速（v_S）随温度的变化（文献中的计算结果：hcp-Fe的波速和预熔化效应（蓝色）^[52]、6600 K时bcc-Fe的波速（橙色）^[58]、5000 K时bcc-Fe₁₃Si₃的Voigt模型波速（青色）以及Voigt-Ruess-Hill（VRH）波速（紫色）^[59] ）

Figure 4. Compressional (v_P) and shear (v_S) wave velocities in hcp-FeH_0.25, hcp-FeO_0.0625 and hcp-FeC_0.0625 as a function of temperature at 360 GPa upon superionic transition (In comparison with previous calculation results of pure hcp-Fe with the effect of pre-melting (blue symbols)^[52], seismic velocities in bcc-Fe at 6600 K (orange symbols)^[58], and seismic velocities in bcc-Fe₁₃Si₃ at 5000 K with Voigt and Voigt-Ruess-Hill (VRH) model, respectively (cyan and purple symbols)^[59].)

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图 5 (a) 内核中地磁场示意图以及随深度变化的各向异性构造变化^[36]，(b) 蓝色区域的超离子态波速模型与观测值的对比^[66]，(c) 最内核（绿色区域）模型波速与观测值的对比^{[22, 27, 67]}

Figure 5. (a) Schematic diagram of poloidal and toroidal geomagnetic field in the inner core (IC) and depth-dependent anisotropic texture change^[36]; (b) the superionic model at the depth of blue area in comparison with geophysical observation data^[66]; (c) the superionic model of innermost inner core (green area) in comparison with geophysical observation data^{[22, 27, 67]}

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表 1 H、O、C在超离子态铁-轻元素合金中的扩散活化焓和超离子态转变温度

Table 1. Diffusion enthalpy of H, O, and C in superionic Fe-light element alloys and their superionic transition temperatures

Alloy	Pressure/GPa	D₀/(cm²·s⁻¹)	ΔH/eV	T_s/K
FeH_0.25	260	0.148	1.58	2000
FeH_0.25	360	0.317	2.14	2230
FeO_0.0625	260	0.079	1.62	2350
FeO_0.0625	360	0.067	1.72	2630
FeC_0.0625	260	0.087	1.83	2600
FeC_0.0625	360	0.074	1.60	2360

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