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

TitleIdentification of post-pyrite phase transitions in SiO2 by a genetic algorithm
Publication TypeJournal Article
Year of Publication2011
AuthorsWu SQ, Umemoto K, Ji M, Wang CZ, Ho KM, Wentzcovitch RM
Journal TitlePhysical Review B
Volume83
Pages184102
Date Published05/16
ISBN Number1098-0121
Accession NumberISI:000290709300002
Keywordscrystal-structure, gas, lower mantle, mgsio3, molecular-dynamics, namgf3, perovskite phase, planets, principles
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 Fe2P--> 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 Fe2P 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.

URL<Go to ISI>://000290709300002
DOI10.1103/PhysRevB.83.184102
Alternate JournalPhys Rev BPhys Rev B