Superionic iron oxide-hydroxide in Earth's deep mantle
Superionic iron oxide-hydroxide in Earth's deep mantle
复制标题
地球深部地幔中的超离子氧化铁-氢氧化物
DOI：
10.1038/s41561-021-00696-2
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发表时间：
2021-03-01
影响因子：
18.3
通讯作者：
Mao, Ho-Kwang
中科院分区：
文献类型：
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作者：
Hou, Mingqiang;He, Yu;Mao, Ho-Kwang
水冰在海王星和天王星等冰行星的深层行星内部的高压和高温条件下成为超离子相，影响内部结构并产生磁场。然而，固体地球只含有含水矿物，冰的数量可以忽略不计。本文结合联合收割机高温高压电导率实验、拉曼光谱和第一性原理模拟，研究了核幔边界附近黄铁矿型FeO 2 Hx（x ≤ 1）中氢的状态。我们发现，当在室温下的压力增加超过73 GPa，对称的羟基键软化和H +（或质子）成为扩散在其晶体学网站附近。在压力下升高温度，氢的扩散率扩展到单个单元电池之外以覆盖整个固体，电导率飙升，表明向超离子态转变，其特征是自由移动的质子和固体FeO 2晶格。高扩散性的氢为电荷和质量提供了新的输运机制，决定了地球深部地幔的电导率和磁性的地球物理行为，以及氧化还原、氢循环和氢同位素混合等地球化学过程。根据电导率实验和第一性原理模拟，在地球深部下地幔的条件下，氢离子通过FeOOH晶格框架自由扩散，电导率迅速增加。
Water ice becomes a superionic phase under the high pressure and temperature conditions of deep planetary interiors of ice planets such as Neptune and Uranus, which affects interior structures and generates magnetic fields. The solid Earth, however, contains only hydrous minerals with a negligible amount of ice. Here we combine high pressure and temperature electrical conductivity experiments, Raman spectroscopy and first-principles simulations to investigate the state of hydrogen in the pyrite-type FeO 2 H x ( x ≤ 1), which is a potential H-bearing phase near the core–mantle boundary. We find that when the pressure increases beyond 73 GPa at room temperature, symmetric hydroxyl bonds are softened and the H + (or proton) becomes diffusive within the vicinity of its crystallographic site. Increasing temperature under pressure, the diffusivity of hydrogen is extended beyond the individual unit cell to cover the entire solid, and the electrical conductivity soars, indicating a transition to the superionic state, which is characterized by freely moving protons and a solid FeO 2 lattice. The highly diffusive hydrogen provides fresh transport mechanisms for charge and mass, which dictate the geophysical behaviours of electrical conductivity and magnetism, as well as geochemical processes of redox, hydrogen circulation and hydrogen isotopic mixing in Earth’s deep mantle. Under conditions of Earth’s deep lower mantle, hydrogen ions diffuse freely through the FeOOH lattice framework and electrical conductivity increases rapidly, according to electrical conductivity experiments and first-principles simulations.