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Stabilization of body-centred cubic iron under inner-core conditions

Nature Geoscience volume 10, pages 312–316 (2017)Cite this article

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Abstract

The Earth’s solid core is mostly composed of iron. However, despite being central to our understanding of core properties, the stable phase of iron under inner-core conditions remains uncertain. The two leading candidates are hexagonal close-packed and body-centred cubic (bcc) crystal structures, but the dynamic and thermodynamic stability of bcc iron under inner-core conditions has been challenged. Here we demonstrate the stability of the bcc phase of iron under conditions consistent with the centre of the core using ab initio molecular dynamics simulations. We find that the bcc phase is stabilized at high temperatures by a diffusion mechanism that arises due to the dynamical instability of the phase at lower temperatures. On the basis of our simulations, we reinterpret experimental data as support for the stability of bcc iron under inner-core conditions. We suggest that the diffusion of iron atoms in solid state may explain both the anisotropy and the low shear modulus of the inner core.

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Figure 1: Modelling N-point transverse acoustic phonon mode (Np) in ideal bcc Fe at 360 GPa.
Figure 2: Time evolution of the computational cell sizes during two molecular dynamics runs.
Figure 3: Results of molecular dynamics simulations in the NPT ensemble at 360 GPa and high T for different sizes of computational cells starting from the bcc and hcp structures.
Figure 4: Structure of bcc iron at 7,000 K and 360 GPa.

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Acknowledgements

Computations were performed using the facilities provided by the Swedish National Infrastructure for Computing (SNIC) at the National Supercomputing Center in Linköping (Sweden). We also wish to thank the Swedish Research Council (VR) for financial support (grants 2013-5767 and 2014-4750). A.B.B., J.Z. and J.F. acknowledge funding from the National Magnetic Confinement Fusion Program of China (2015GB118000) and the China Scholarship Council. S.I.S. acknowledges Linköping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM) and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009 00971).

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Authors and Affiliations

  1. Department of Theoretical Physics, Condensed Matter Theory, AlbaNova University Center, Royal Institute of Technology (KTH), 106 91 Stockholm, Sweden

    Anatoly B. Belonoshko, Timofei Lukinov & Jie Fu

  2. Key Laboratory of Materials Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education, 116024 Dalian, China

    Jie Fu & Jijun Zhao

  3. Chilean Committee of Nuclear Energy (CCHEN), Casilla 188-D, Santiago, Chile

    Sergio Davis

  4. Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-58183 Linköping, Sweden

    Sergei I. Simak

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  1. Anatoly B. Belonoshko
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  2. Timofei Lukinov
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  3. Jie Fu
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  4. Jijun Zhao
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  5. Sergio Davis
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Contributions

A.B.B. designed the study, performed calculations and wrote the paper; T.L. performed calculations and wrote the paper; J.F. and S.D. performed calculations and discussed the paper; J.Z. discussed the paper; S.I.S. performed the calculations and wrote the paper; all authors discussed the results and contributed to paper writing.

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Correspondence to Anatoly B. Belonoshko.

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Belonoshko, A., Lukinov, T., Fu, J. et al. Stabilization of body-centred cubic iron under inner-core conditions. Nature Geosci 10, 312–316 (2017). https://doi.org/10.1038/ngeo2892

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