Identification of post-pyrite phase transitions in SiO2 by a genetic algorithm

Shunqing Wu, Koichiro Umemoto, Min Ji, Cai Zhuang Wang, Kai Ming Ho, Renata M Wentzcovitch

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32 Scopus citations

Abstract

Using a first-principles genetic algorithm we predict an Fe2P phase is the first post-pyrite phase of SiO2 at low temperatures. This contrasts with a recently predicted cotunnite phase. Static enthalpy differences between these two phases are small near the transition pressure (0.69 TPa). While quasiharmonic free energy calculations predict an Fe 2P-→cotunnite-type transition with increasing temperature, another phase, NbCoB type, is identified as being structurally and energetically intermediate between Fe2P and cotunnite phases. This structure suggests a possible temperature-induced gradual transformation between Fe 2P and cotunnite phases. This finding would change our understanding of how planet-forming silicates, for example, MgSiO3 post-perovskite and its solid solutions, dissociate into elementary oxides at thermodynamic conditions expected in the interior of solar giants and exoplanets.

Original languageEnglish (US)
Article number184102
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume83
Issue number18
DOIs
StatePublished - May 16 2011

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