Stability of hcp phase and temperature variation of axial ratio of iron near Earth-core conditions

Details Stability of hcp phase and temperature variation of axial ratio of iron near Earth-core conditions Stability of hcp phase and temperature variation of axial ratio of iron near Earth-core conditions

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.p41c1291g&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #P41C-1291

Mathematics

Logic

3924 High-Pressure Behavior, 5724 Interiors (8147)

Scientific paper

Pseudopotential-based quasi-harmonic calculations of the properties of iron at elevated pressures and temperatures reveal that the hexagonal close-packed (hcp) phase of iron is stable relative to the body-centered cubic (bcc) structure at conditions of the inner core. Ab-initio quantum mechanical molecular dynamic (MD) simulations using the VASP package (pseudotentials with plane-wave basis) confirm that the bcc structure is energetically unfavorable and mechanically unstable relative to tetragonal strains. Therefore, inner-core properties such as the seismologically observed anisotropy of compressional-wave velocities are most likely attributable to the hcp rather than the bcc phase of iron. We obtain the calculated temperature variation of c/a ratio at Earth core pressure in agreement with previous theoretical studies which show that the c/a ratio increases with increasing temperature. Further ab- initio molecular dynamics studies will investigate the elastic constant tensor of hcp iron, important for understanding the origin of inner core anisotropy. There is also need for high resolution measurements for c/a ratio at high pressures and temperatures to be compared with simulation results.

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