Superionic Silica-Water and Silica-Hydrogen Compounds in the Deep Interiors of Uranus and Neptune
Superionic Silica-Water and Silica-Hydrogen Compounds in the Deep Interiors of Uranus and Neptune
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DOI：
10.1103/physrevlett.128.035702
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发表时间：
2022-01-21
影响因子：
8.6
通讯作者：
Sun, Jian
中科院分区：
文献类型：
--
作者：
Gao, Hao;Liu, Cong;Sun, Jian
硅、水和氢被认为是天体的主要成分，对天王星和海王星等巨行星的形成和演化有重要影响。因此，研究它们在行星条件下的状态和可能的反应是非常重要的。在此，我们利用先进的晶体结构搜索和Si-O-H系统的第一性原理计算，发现硅-水化合物（SiO2）2（H2O）和硅-氢化合物SiO2 H2可以分别在450和650 GPa以上的高压下存在。进一步的模拟显示，在对应于天王星和海王星内部的高压和高温条件下，这些化合物表现出超离子行为，其中质子像液体一样自由扩散，而硅和氧框架固定为固体。因此，这些超离子硅水和硅氢化合物可以被认为是巨星深部地幔或核的重要组成部分，这也为它们的异常磁场提供了另一种来源。最常见的天然材料在高压下的这些意想不到的物理和化学性质为理解一些深奥的问题提供了关键线索，包括巨行星核心的分层和侵蚀，并为建立太阳巨星和系外行星的可靠模型提供了线索。
Silica, water, and hydrogen are known to be the major components of celestial bodies, and have significant influence on the formation and evolution of giant planets, such as Uranus and Neptune. Thus, it is of fundamental importance to investigate their states and possible reactions under the planetary conditions. Here, using advanced crystal structure searches and first-principles calculations in the Si-O-H system, we find that a silica-water compound (SiO2)2(H2O) anda silica-hydrogen compound SiO2H2 can exist under high pressures above 450 and 650 GPa, respectively. Further simulations reveal that, at high pressure and high temperature conditions corresponding to the interiors of Uranus and Neptune, these compounds exhibit superionic behavior, in which protons diffuse freely like liquid while the silicon and oxygen framework is fixed as solid. Therefore, these superionic silica-water and silica-hydrogen compounds could be regarded as important components of the deep mantle or core of giants, which also provides an alternative origin for their anomalous magnetic fields. These unexpected physical and chemical properties of the most common natural materials at high pressure offer key clues to understand some abstruse issues including demixing and erosion of the core in giant planets, and shed light on building reliable models for solar giants and exoplanets.