High-pressure behavior of the Fe—S system and composition of the Earth's inner core

Bazhanova, Zulfiya G.; Roizen, Valery V.; Oganov, Artem R.

doi:10.3367/ufnr.2017.03.038079

Cited by 11 publications

(3 citation statements)

References 77 publications

(106 reference statements)

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“…When the fitting is made with a reference pressure of 1 bar, we obtain V 0 = 133(1) Å 3 and K 0 = 226(8) GPa with K ' 0 = 4 (fixed). They are generally consistent with those from theoretical calculations at 0 K when considering the temperature difference (Bazhanova et al, ).…”

Section: Resultssupporting

confidence: 90%

“…Finally, 20 peaks from the sample grew and became spotty in a 2D diffraction image in 1 hr (Figures b and S1a). All the new peaks fully match those of the orthorhombic phase with Pnma space group (Figure c and Table S1), which has been predicted by theory (Bazhanova et al, ). Diffraction peaks from SiO 2 were not observed in the present experiments; crystallization of SiO 2 glass is known to be quite sluggish (e.g., Tateno et al, , ; Komabayashi et al, ).…”

Section: Resultssupporting

confidence: 81%

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Fe₂S: The Most Fe‐Rich Iron Sulfide at the Earth's Inner Core Pressures

Tateno

Hirose

Suzuki

et al. 2019

Geophysical Research Letters

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We examined the phase relation of Fe2S to 306 GPa and 3,000 K and found that Fe2S forms an orthorhombic structure with space group Pnma above 190 GPa. Reexamination of previous X‐ray diffraction data demonstrated that hexagonal close‐packed Fe coexists with Pnma Fe2S at >2,700 K and ~290 GPa, while it concurs with CsCl (B2)‐type stoichiometric FeS at lower temperatures. Our results indicate that Fe2S is the most Fe‐rich iron sulfide above ~250 GPa where Fe3S is not stable. It is most likely that eutectic melting occurs between Fe and Fe2S at 330 GPa corresponding to inner core boundary conditions, instead of between Fe and Fe3S below 250 GPa. The compression curve of Fe2S obtained to 294 GPa shows that it is not dense enough to account for the inner core density, suggesting that the Fe‐Fe2S eutectic liquid gives the maximum sulfur concentration in the outer core.

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Section: Resultssupporting

confidence: 90%

Section: Resultssupporting

confidence: 81%

Fe₂S: The Most Fe‐Rich Iron Sulfide at the Earth's Inner Core Pressures

Tateno

Hirose

Suzuki

et al. 2019

Geophysical Research Letters

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“…Shock experiments by Ahrens and Jeanloz () suggest that cubic pyrite is stable up to 320 GPa. While recent theory suggests that C2/m ‐FeS 2 may be stable at inner core conditions (Bazhanova et al, ), experimental equations of state are also not presently available for this phase. In a recent review, Li and Fei () suggest that Fe 7 C 3 is favored over Fe 3 C as the liquidus phase of the Fe‐C system at pressures above 7 GPa and therefore favored as a phase in the inner core.…”

Section: Extrapolation To Inner Core Conditionsmentioning

confidence: 99%

Equations of State and Anisotropy of Fe‐Ni‐Si Alloys

et al. 2018

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We present powder X‐ray diffraction data on body centered cubic (bcc)‐ and hexagonal close packed (hcp)‐structured Fe0.91Ni0.09 and Fe0.8Ni0.1Si0.1 at 300 K up to 167 and 175 GPa, respectively. The alloys were loaded with tungsten powder as a pressure calibrant and helium as a pressure transmitting medium into diamond anvil cells, and their equations of state and axial ratios were measured with high statistical quality. These equations of state are combined with thermal parameters from previous reports to improve the extrapolation of the density, adiabatic bulk modulus, and bulk sound speed to the pressures and temperatures of Earth's inner core. We propagate uncertainties and place constraints on the composition of Earth's inner core by combining these results with available data on light‐element alloys of iron and seismic observations. For example, the addition of 4.3 to 5.3 wt% silicon to Fe0.95Ni0.05 alone can explain geophysical observations of the inner core boundary, as can up to 7.5 wt% sulfur with negligible amounts of silicon and oxygen. Our findings favor an inner core with less than ∼2 wt% oxygen and less than 1 wt% carbon, although uncertainties in electronic and anharmonic contributions to the equations of state may shift these values. The compositional space widens toward the center of the Earth, considering inner core seismic gradients. We demonstrate that hcp‐Fe0.91Ni0.09 and hcp‐Fe0.8Ni0.1Si0.1 have measurably greater c/a axial ratios than those of hcp‐Fe over the measured pressure range. We further investigate the relationship between the axial ratios, their pressure derivatives, and elastic anisotropy of hcp‐structured materials.

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