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 language | English (US) |
---|---|
Article number | 184102 |
Journal | Physical Review B - Condensed Matter and Materials Physics |
Volume | 83 |
Issue number | 18 |
DOIs | |
State | Published - May 16 2011 |