Computational searches for iron oxides at high pressures

We have used density-functional-theory methods and the ab initio random structure searching (AIRSS) approach to predict stable structures and stoichiometries of mixtures of iron and oxygen at high pressures. Searching was performed for 12 different stoichiometries at pressures of 100, 350 and 500 GPa, which involved relaxing more than 32 000 structures. We find that Fe2O3 and FeO2 are the only phases stable to decomposition at 100 GPa, while at 350 and 500 GPa several stoichiometries are found to be stable or very nearly stable. We report a new structure of Fe2O3 with P2(1)2(1)2(1)2 symmetry which is found to be more stable than the known Rh2O3(II) phase at pressures above  ∼233 GPa. We also report two new structures of FeO, with Pnma and R3m symmetries, which are found to be stable within the ranges 195-285 GPa and 285-500 GPa, respectively, and two new structures of Fe3O4 with Pca21 and P21/c symmetries, which are found to be stable within the ranges 100-340 GPa and 340-500 GPa, respectively. Finally, we report two new structures of Fe4O5 with P42/n and [Formula: see text] symmetries, which are found to be stable within the ranges 100-231 GPa and 231-500 GPa, respectively. Our new structures of Fe3O4 and Fe4O5 are found to have lower enthalpies than their known structures within their respective stable pressure ranges.

[1]  R. Cohen,et al.  Magnetic Collapse in Transition Metal Oxides at High Pressure: Implications for the Earth , 1997, Science.

[2]  D. Vanderbilt,et al.  Soft self-consistent pseudopotentials in a generalized eigenvalue formalism. , 1990, Physical review. B, Condensed matter.

[3]  Thermodynamic Stability of Fe/O Solid Solution at Inner‐Core Conditions , 2000, cond-mat/0002208.

[4]  R. Cohen,et al.  Composition and temperature of Earth's inner core , 1997 .

[5]  G. Morard,et al.  Melting of Iron at Earth’s Inner Core Boundary Based on Fast X-ray Diffraction , 2013, Science.

[6]  S. Ono,et al.  In situ X-ray observation of phase transformation in Fe2O3 at high pressures and high temperatures , 2005 .

[7]  Marie-Hélène Lemée-Cailleau,et al.  Crystal structure of ammonia monohydrate phase II. , 2009, Journal of the American Chemical Society.

[8]  London,et al.  Oxygen in the Earth's core: a first-principles study , 1999 .

[9]  R. Needs,et al.  Stable phases of iron at terapascal pressures , 2009, Journal of physics. Condensed matter : an Institute of Physics journal.

[10]  M. Gillan,et al.  Composition and temperature of the Earth's core constrained by combining ab initio calculations and seismic data , 2002 .

[11]  S. Ju,et al.  Pressure-induced crystal structure and spin-state transitions in magnetite (Fe3O4). , 2012, Journal of the American Chemical Society.

[12]  M. Payne,et al.  Second-order k"p perturbation theory with Vanderbilt pseudopotentials and plane waves , 2000 .

[13]  T. Miyazaki,et al.  Inverse versus normal NiAs structures as high-pressure phases of FeO and MnO , 1997, cond-mat/9707139.

[14]  H. Mao,et al.  In situ structure determination of the high-pressure phase of Fe3O4 , 1999 .

[15]  Y. Ohishi,et al.  Phase Transition of FeO and Stratification in Earth’s Outer Core , 2011, Science.

[16]  Matt Probert,et al.  First principles methods using CASTEP , 2005 .

[17]  R. Needs,et al.  Crystal structure of ammonia dihydrate II. , 2012, The Journal of chemical physics.

[18]  Z. Fang,et al.  First-principles study on electronic structures and phase stability of MnO and FeO under high pressure , 1999 .

[19]  Yanming Ma,et al.  Structure of the metallic ζ-phase of oxygen and isosymmetric nature of the ε-ζ phase transition : Ab initio simulations , 2007 .

[20]  R. Ahuja,et al.  The structure of the metallic high-pressure Fe3O4 polymorph : experimental and theoretical study , 2003 .

[21]  M. Gillan,et al.  First-principles modelling of Earth and planetary materials at high pressures and temperatures , 2006 .

[22]  S. Ono,et al.  High pressure and high temperature phase transitions of FeO , 2004 .

[23]  Y. Fei,et al.  Sound velocity in iron carbide (Fe3C) at high pressure: Implications for the carbon content of the Earth's inner core , 2009 .

[24]  S. Sutton,et al.  Discovery of the recoverable high-pressure iron oxide Fe4O5 , 2011, Proceedings of the National Academy of Sciences.

[25]  Chris J Pickard,et al.  Ab initio random structure searching , 2011, Journal of physics. Condensed matter : an Institute of Physics journal.

[26]  H. Mao,et al.  Magnetism in FeO at Megabar Pressures from X-Ray Emission Spectroscopy , 1999 .

[27]  Y. Ohishi,et al.  Phase transition boundary between B1 and B8 structures of FeO up to 210 GPa , 2010 .

[28]  F. Stillinger.  Exponential multiplicity of inherent structures , 1999 .

[29]  R. Cohen,et al.  Elasticity of iron at the temperature of the Earth's inner core , 2001, Nature.

[30]  V. Prakapenka,et al.  Equation of state and phase diagram of FeO , 2011 .

[31]  Chris J. Pickard,et al.  Extrapolative approaches to Brillouin-zone integration , 1999 .

[32]  S. Russo,et al.  Hybrid density functional theory study of the high-pressure polymorphs of α -Fe2 O3 hematite , 2009 .

[33]  Chris J. Pickard,et al.  Metallization of aluminum hydride at high pressures: A first-principles study , 2007 .

[34]  S. Stølen,et al.  Equation of state of magnetite and its high-pressure modification: Thermodynamics of the Fe-O system at high pressure , 2000 .

[35]  R. Needs,et al.  Controlling the bonding and band gaps of solid carbon monoxide with pressure. , 2011, Physical review letters.

[36]  Burke,et al.  Generalized Gradient Approximation Made Simple. , 1996, Physical review letters.

[37]  Raymond Jeanloz,et al.  Breakdown of the Mott-Hubbard State in Fe 2 O 3 : A First-Order Insulator-Metal Transition with Collapse of Magnetism at 50 GPa , 1999 .

[38]  S. Ono,et al.  In situ x-ray observation of the phase transformation of Fe2O3 , 2005 .

[39]  B. Wood.  Carbon in the core , 1993 .

[40]  Chris J Pickard,et al.  High-pressure phases of silane. , 2006, Physical review letters.

[41]  R. Jeanloz,et al.  High pressure collapse of magnetism in Fe0.94O: Mössbauer spectroscopy beyond 100 GPa , 1997 .

[42]  R. Needs,et al.  Persistence and eventual demise of oxygen molecules at terapascal pressures. , 2011, Physical review letters.

[43]  R. Ahuja,et al.  High-pressure structural studies of hematite Fe 2 O 3 , 2002 .