2011年
Prediction of a hexagonal SiO2 phase affecting stabilities of MgSiO3and CaSiO3at multimegabar pressures
Proceedings of the National Academy of Sciences of the United States of America
- ,
- 巻
- 108
- 号
- 4
- 開始ページ
- 1252
- 終了ページ
- 1255
- 記述言語
- 英語
- 掲載種別
- 研究論文(学術雑誌)
- DOI
- 10.1073/pnas.1013594108
Ultrahigh-pressure phase relationship of SiO2 silica in multimegabar pressure condition is still quite unclear. Here, we report a theoretical prediction on a previously uncharacterized stable structure of silica with an unexpected hexagonal Fe2P-type form. This phase, more stable than the cotunnite-type structure, a previously postulated postpyrite phase, was discovered to stabilize at 640 GPa through a careful structure search by means of ab initio density functional computations over various structure models. This is the first evidential result of the pressure-induced phase transition to the Fe2P-type structure among all dioxide compounds. The crystal structure consists of closely packed, fairly regular SiO9 tricapped trigonal prisms with a significantly compact lattice. Additional investigation further elucidates large effects of this phase change in SiO 2 on the stability of MgSiO3 and CaSiO3 at multimegabar pressures. A postperovskite phase of MgSiO3 breaks down at 1.04 TPa along an assumed adiabat of super-Earths and yields Fe 2P-type SiO2 and CsCl (B2)-type MgO. CaSiO3 perovskite, on the other hand, directly dissociates into SiO2 and metallic CaO, skipping a postperovskite polymorph. Predicted ultrahigh-pressure and temperature phase diagrams of SiO2, MgSiO3, and CaSiO3 indicate that the Fe2P-type SiO2 could be one of the dominant components in the deep mantles of terrestrial exoplanets and the cores of gas giants.
- リンク情報
- ID情報
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- DOI : 10.1073/pnas.1013594108
- ISSN : 0027-8424
- ORCIDのPut Code : 49519588
- PubMed ID : 21209327
- SCOPUS ID : 79952126784