Superionic silica-water and silica-hydrogen compounds under high pressure

Abstract

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) and a 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.

13 pages, 4 figures

References in corpus (5)

• High-pressure phases of silane
• Constraining the Origins of Neptune's Carbon Monoxide Abundance with CARMA Millimeter-wave Observations
• Thermal evolution of Uranus and Neptune I: adiabatic models
• Enhancing Crystal Structure Prediction by decomposition methods based on graph theory
• Ultrahigh-Pressure Magnesium Hydrosilicates as Reservoirs of Water in Early Earth

Cited by in corpus (6)

• Ultrahigh-Pressure Magnesium Hydrosilicates as Reservoirs of Water in Early Earth
• Stochastic and Mixed Density Functional Theory within the projector augmented wave formalism for the simulation of warm dense matter
• Partially Diffusive Helium-Silica Compound in the Deep Interiors of Giant Planets
• Ab initio superionic-liquid phase diagram of Fe1-xOx under Earth's inner core conditions
• The linear-mixing approximation in silica-water mixtures at planetary conditions
• Icy or rocky? Convective or stable? New interior models of Uranus and Neptune