Partially Diffusive Helium-Silica Compound under High Pressure
Cong Liu1,2, Junjie Wang1, Xin Deng3, Xiaomeng Wang1, Chris J. Pickard4,5, Ravit Helled6, Zhongqing Wu3, Hui-Tian Wang1, Dingyu Xing1, and Jian Sun1*
1National Laboratory of Solid State Microstructures, School of Physics and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China 2Departament de Física, Universitat Politècnica de Catalunya, Campus Nord B4-B5, E-08034 Barcelona, Spain 3Laboratory of Seismology and Physics of Earth's Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China 4Department of Materials Science & Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK 5Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan 6Institute for Computational Science, Center for Theoretical Astrophysics & Cosmology, University of Zurich, Switzerland
Abstract：Helium is the second most abundant element in the universe, and together with silica, they are important components of giant planets. Exploring the reactivity and state of helium and silica under high pressure is crucial for understanding of the evolution and internal structure of giant planets. Here, using first-principles calculations and crystal structure predictions, we identify four stable phases of a helium-silica compound with seven/eight-coordinated silicon atoms at pressure of 600–4000 GPa, corresponding to the interior condition of the outer planets in the solar system. The density of HeSiO$_{2}$ agrees with current structure models of the planets. This helium-silica compound exhibits a superionic-like helium diffusive state under the high-pressure and high-temperature conditions along the isentropes of Saturn, a metallic fluid state in Jupiter, and a solid state in the deep interiors of Uranus and Neptune. These results show that helium may affect the erosion of the rocky core in giant planets and may help to form a diluted core region, which not only highlight the reactivity of helium under high pressure but also provide evidence helpful for building more sophisticated interior models of giant planets.
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2022, Vol. 39 
