Crystal Structures of Core Materials

Isothermal equation of state and phase stability of Fe5Si3 up to 96 GPa and 3000 K

“…These results show that Fe 5 Si 3 is not stable at high temperatures and pressures. While X‐ray diffraction alone, as used here, cannot unequivocally demonstrate the stability of phases, the evidence presented in this study is consistent with theoretical predictions that intermediate silicides are unstable at core conditions with respect to a Fe 3 Si‐like Fe‐Si alloy structure and B2 FeSi [ Brosh et al ., ; Zhang and Oganov , ; Caracas , ]. Experimental studies have shown that at pressures above ~60 GPa, DO 3 Fe‐Si alloys decompose into Si‐poor hcp Fe‐Si alloy and Si‐rich B2 phase [ Fischer et al ., ; Lin et al ., , ; Tateno et al ., ].…”

“…High‐pressure and temperature‐experimental studies of the Fe‐FeSi system suggest that it may simplify at core conditions relative to ambient pressure, due to a lack of compositional intermediate phases with distinct crystal structures [ Kuwayama et al ., ; Fischer et al ., ; Tateno et al ., ]. Theoretical work on the Fe‐FeSi phase diagram has shown that the intermediate stoichiometric phase Fe 5 Si 3 is not stable with respect to the ordered alloy phase (DO 3 , isostructural with Fe 3 Si) and FeSi at the pressures and temperature conditions of the Earth's core [ Brosh et al ., ; Zhang and Oganov , ; Caracas , ]. Experimental work on the Fe‐FeSi system provides support for this prediction, but the stability of Fe 5 Si 3 at high pressure and high temperature has not been experimentally determined.…”

The iron spin transition of deep nitrogen-bearing mineral Fe3N1.2 at high pressure

“…On the contrary, the spin transition pressures are comparable between Fe 7 N 3 and Fe 7 C 3 . We note that Fe 7 N 3 , Fe 7 C 3 , and Fe 3 N 1.2 have a hexagonal lattice, while Fe 3 C has an orthorhombic structure [Caracas, 2016].…”

Geoscience material structures prediction via CALYPSO methodology

“…While both experiments and calculations have made great strides in studies of volatile elements interacting with iron, there are many more challenges ahead before a full understanding of the composition of heavy planetary cores can emerge. Other light elements could be present in the core, with magnesium a prime candidate; more studies are needed on Mg-Fe mixtures, which might tilt the balance of whether magnesium can partition in iron instead of silicates [15] . The ternary phase diagrams Fe-Ni-X for some volatile element X might look different than both the binary phase diagrams Fe-X or Ni-X, and this would further influence the volatiles'…”