Unveiling the effect of Ni on the formation and structure of Earth’s inner core
Edited by Alexandra Navrotsky, Arizona State University, Tempe, AZ; received September 21, 2023; accepted December 9, 2023
Significance
The Earth’s inner core growth is a key process for understanding Earth’s evolution. This process is inherently related to the crystallization properties of the core’s constituents, primarily Fe, Ni, and some light elements. This work demonstrates that the core’s second most abundant element, Ni, strongly affects Fe’s crystallization process. Ni can stabilize the bcc phase and accelerate Fe’s crystallization under core pressures. The simulation results suggest that alloying Fe with Ni can promote the coexistence of the bcc and hcp phases in the solid inner core. This is critical in understanding the inner core’s nucleation and the origin of its complex solid structure.
Abstract
Ni is the second most abundant element in the Earth’s core. Yet, its effects on the inner core’s structure and formation process are usually disregarded because of its electronic and size similarity with Fe. Using ab initio molecular dynamics simulations, we find that the bcc phase can spontaneously crystallize in liquid Ni at temperatures above Fe’s melting point at inner core pressures. The melting temperature of Ni is shown to be 700 to 800 K higher than that of Fe at 323 to 360 GPa. hcp, bcc, and liquid phase relations differ for Fe and Ni. Ni can be a bcc stabilizer for Fe at high temperatures and inner core pressures. A small amount of Ni can accelerate Fe’s crystallization at core pressures. These results suggest that Ni may substantially impact the structure and formation process of the solid inner core.
Data, Materials, and Software Availability
All study data are included in the article and/or SI Appendix.
Acknowledgments
Work at Xiamen University was supported by the National Natural Science Foundation of China Grant No. 42374108. Work at Columbia University was supported by the National Science Foundation (NSF) Grants Nos. EAR-2000850 and EAR-1918126. Work at Iowa State University was supported by the NSF Grant No. EAR-1918134. R.M.W. was partially supported by Department of Energy Award DE-SC0019759. X.L. and B.D. were supported by Japan Society for the Promotion of Science KAKENHI (Grants-in-Aid for Scientific Research) Grant No. JP21K14656. We acknowledge the computer resources from the Extreme Science and Engineering Discovery Environment, supported by the NSF grants #2138259, #2138286, #2138307, #2137603, and #2138296. Molecular dynamics simulations were supported by the Numerical Materials Simulator supercomputer at the National Institute for Materials Science. S. Fang and T. Wu from Information and Network Center of Xiamen University are acknowledged for the help with the graphics processing unit computing. The Tan Kah Kee Supercomputing Center is acknowledged for the high-performance computing resources.
Author contributions
Y.S., M.I.M., R.M.W., and K.-M.H. designed research; Y.S. and M.I.M. performed research; Y.S., M.I.M., X.L., and B.D. contributed new reagents/analytic tools; Y.S., M.I.M., F.Z., X.L., B.D., C.-Z.W., R.M.W., and K.-M.H. analyzed data; and Y.S., M.I.M., F.Z., C.-Z.W., R.M.W., and K.-M.H. wrote the paper.
Competing interests
The authors declare no competing interest.
Supporting Information
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Copyright © 2024 the Author(s). Published by PNAS. This article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).
Data, Materials, and Software Availability
All study data are included in the article and/or SI Appendix.
Submission history
Received: September 21, 2023
Accepted: December 9, 2023
Published online: January 18, 2024
Published in issue: January 23, 2024
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Acknowledgments
Work at Xiamen University was supported by the National Natural Science Foundation of China Grant No. 42374108. Work at Columbia University was supported by the National Science Foundation (NSF) Grants Nos. EAR-2000850 and EAR-1918126. Work at Iowa State University was supported by the NSF Grant No. EAR-1918134. R.M.W. was partially supported by Department of Energy Award DE-SC0019759. X.L. and B.D. were supported by Japan Society for the Promotion of Science KAKENHI (Grants-in-Aid for Scientific Research) Grant No. JP21K14656. We acknowledge the computer resources from the Extreme Science and Engineering Discovery Environment, supported by the NSF grants #2138259, #2138286, #2138307, #2137603, and #2138296. Molecular dynamics simulations were supported by the Numerical Materials Simulator supercomputer at the National Institute for Materials Science. S. Fang and T. Wu from Information and Network Center of Xiamen University are acknowledged for the help with the graphics processing unit computing. The Tan Kah Kee Supercomputing Center is acknowledged for the high-performance computing resources.
Author contributions
Y.S., M.I.M., R.M.W., and K.-M.H. designed research; Y.S. and M.I.M. performed research; Y.S., M.I.M., X.L., and B.D. contributed new reagents/analytic tools; Y.S., M.I.M., F.Z., X.L., B.D., C.-Z.W., R.M.W., and K.-M.H. analyzed data; and Y.S., M.I.M., F.Z., C.-Z.W., R.M.W., and K.-M.H. wrote the paper.
Competing interests
The authors declare no competing interest.
Notes
This article is a PNAS Direct Submission.
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Unveiling the effect of Ni on the formation and structure of Earth’s inner core, Proc. Natl. Acad. Sci. U.S.A.
121 (4) e2316477121,
https://doi.org/10.1073/pnas.2316477121
(2024).
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