Hidden carbon in Earth’s inner core revealed by shear softening in dense Fe
            <sub>7</sub>
            C
            <sub>3</sub>

Chen, Bin; Li, Zeyu; Zhang, Dongzhou; Liu, Jiachao; Hu, Michael Y.; Zhao, Jiyong; Bi, Weihong; Ercan, E.; Xiao, Yuming; Chow, Paul; Li, Jie

doi:10.1073/pnas.1411154111

Cited by 102 publications

(129 citation statements)

References 41 publications

Supporting

Mentioning

112

Contrasting

Order By: Relevance

“…Comparison of our results for h ‐Fe 7 C 3 with the experimental data of Chen et al . [] and Prescher et al . [] for G , K T , V P , and V S .…”

Section: Resultsmentioning

confidence: 99%

“…As shown in previous studies, PBE works well for the description of the Fe‐C system [ Mookherjee et al ., ; Oganov et al ., ; Raza et al ., ]. Both experiments [ Prescher et al ., ; Chen et al ., ] and calculations [ Mookherjee et al ., ; Raza et al ., ] show the disappearance of magnetic moments at high pressures (53 GPa h ‐Fe 7 C 3 and 70 GPa for o ‐Fe 7 C 3 ), so we performed nonspin polarized calculations for pressures above 70 GPa.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Thermoelasticity of Fe₇C₃ under inner core conditions

Vočadlo

Brodholt

et al. 2016

JGR Solid Earth

View full text Add to dashboard Cite

It has recently been reported, on the basis of extrapolated experimental data, that the iron carbide, Fe7C3, has shear wave velocities and a Poisson's ratio consistent with the seismological values for the Earth's inner core and thus that Fe7C3 is a strong candidate for the inner core composition. In this study, using ab initio molecular dynamics simulations, we report the thermoelastic properties of Fe7C3 at 350 GPa up to its melting temperature. Due to significant elastic softening prior to melting, the calculated elastic properties, including wave velocities, do indeed agree well with those from seismology. However, the density was found to be much too low (by ~8%) when compared to geophysical data, and therefore, Fe7C3 must be ruled out as a major component of the Earth's inner core.

show abstract

“…Comparison of our results for h ‐Fe 7 C 3 with the experimental data of Chen et al . [] and Prescher et al . [] for G , K T , V P , and V S .…”

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Thermoelasticity of Fe₇C₃ under inner core conditions

Vočadlo

Brodholt

et al. 2016

JGR Solid Earth

View full text Add to dashboard Cite

show abstract

“…Fe 7 C 3 exhibits the anomalously low V S at core pressures, which in turn raises up the values of V P / V S and ν . This anomalously low V S is proposed to be caused by the shear softening associated with a pressure‐induced spin‐pairing transition of iron in Fe 7 C 3 [ Chen et al , ]. We note that iron oxides (Fe 3 O 4 magnetite and Fe 0.94 O wüstite) exhibit extremely high Poisson's ratios at pressures of less than 20 GPa largely due to the pressure‐induced mode softening of the C 44 elastic constant [ Kantor et al , ; Lin et al , ].…”

Section: Discussionmentioning

confidence: 99%

Seismic parameters of hcp‐Fe alloyed with Ni and Si in the Earth's inner core

et al. 2016

Self Cite

View full text Add to dashboard Cite

Iron alloyed with Ni and Si has been suggested to be a major component of the Earth's inner core. High‐pressure results on the combined alloying effects of Ni and Si on seismic parameters of iron are thus essential for establishing satisfactory geophysical and geochemical models of the region. Here we have investigated the compressional (VP) and shear (Vs) wave velocity‐density (ρ) relations, Poisson's ratio (ν), and seismic heterogeneity ratios (dlnρ/dlnVP, dlnρ/dlnVS, and dlnVP/dlnVS) of hcp‐Fe and hcp‐Fe86.8Ni8.6Si4.6 alloy up to 206 GPa and 136 GPa, respectively, using multiple complementary techniques. Compared with the literature velocity values for hcp‐Fe and Fe‐Ni‐Si alloys, our results show that the combined addition of 9.0 wt % Ni and 2.3 wt % Si slightly increases the VP but significantly decreases the VS of hcp‐Fe at a given density relevant to the inner core. Such distinct alloying effects on velocities of hcp‐Fe produce a high ν of about 0.40 for the alloy at inner core densities, which is approximately 20% higher than that for hcp‐Fe. Analysis of the literature high P‐T results on VP and VS of Fe alloyed with light elements shows that high temperature can further enhance the ν of hcp‐Fe alloyed with Ni and Si. Most significantly, the derived seismic heterogeneity ratios of this hcp alloy present a better match with global seismic observations. Our results provide a multifactored geophysical constraint on the compositional model of the inner core which is consistent with silicon being a major light element alloyed with Fe and 5 wt % Ni.

show abstract

“…At pressures above this spin transition, the sound velocity increases with pressure at a much lower rate, which may explain the anomalously low sound velocity in the Earth's core without the need to invoke partial melting or high-temperature effects [15].…”

Section: Introductionmentioning

confidence: 99%

First-principles calculations of properties of orthorhombic iron carbideFe7C3at the Earth's core conditions

et al. 2015

View full text Add to dashboard Cite

A recently discovered phase of orthorhombic iron carbide o-Fe 7 C 3 [Prescher et al., Nat. Geosci. 8, 220 (2015)] is assessed as a potentially important phase for interpretation of the properties of the Earth's core. In this paper, we carry out first-principles calculations on o-Fe 7 C 3 , finding properties to be in broad agreement with recent experiments, including a high Poisson's ratio (0.38). Our enthalpy calculations suggest that o-Fe 7 C 3 is more stable than Eckstrom-Adcock hexagonal iron carbide (h-Fe 7 C 3 ) below approximately 100 GPa. However, at 150 GPa, the two phases are essentially degenerate in terms of Gibbs free energy, and further increasing the pressure towards Earth's core conditions stabilizes h-Fe 7 C 3 with respect to the orthorhombic phase. Increasing the temperature tends to stabilize the hexagonal phase at 360 GPa, but this trend may change beyond the limit of the quasiharmonic approximation.

show abstract

Hidden carbon in Earth’s inner core revealed by shear softening in dense Fe ₇ C ₃

Cited by 102 publications

References 41 publications

Thermoelasticity of Fe₇C₃ under inner core conditions

Thermoelasticity of Fe₇C₃ under inner core conditions

Seismic parameters of hcp‐Fe alloyed with Ni and Si in the Earth's inner core

First-principles calculations of properties of orthorhombic iron carbideFe7C3at the Earth's core conditions

Contact Info

Product

Resources

About

Hidden carbon in Earth’s inner core revealed by shear softening in dense Fe 7 C 3

Cited by 102 publications

References 41 publications

Thermoelasticity of Fe7C3 under inner core conditions

Thermoelasticity of Fe7C3 under inner core conditions

Seismic parameters of hcp‐Fe alloyed with Ni and Si in the Earth's inner core

First-principles calculations of properties of orthorhombic iron carbideFe7C3at the Earth's core conditions

Contact Info

Product

Resources

About

Hidden carbon in Earth’s inner core revealed by shear softening in dense Fe ₇ C ₃

Thermoelasticity of Fe₇C₃ under inner core conditions

Thermoelasticity of Fe₇C₃ under inner core conditions