SEARCH FOR STABLE STRUCTURES FOR THE NICKEL-SULFUR SYSTEM AND COMPARISON WITH THE IRON-SULFUR SYSTEM

The core of the Earth consists mainly of iron and nickel, forming an iron-nickel alloy. At the same time, sulfur is one of the potential candidates for the role of a light element in the inner core. To date, many theoretical studies have been conducted by quantum chemical modeling to search for intermediate compositions and structures in systems such as Fe-C, Fe-H, Fe-O, Fe-Si, Fe-S and Fe-P up to pressures of 400 GPa.

Despite extensive research on the iron-light element systems, to date no mineralogical model of the Earth's core has been created that fully corresponds to the observed seismological data. A possible reason for this discrepancy may be insufficient consideration of the influence of the core's key alloying element, nickel. Theoretical studies for the nickel-light element system at high pressures have not been sufficiently carried out. Therefore, it is necessary to conduct more in-depth studies of these binary systems in order to further study and identify possible intermediates in triple Fe-Ni-S systems.

1. Sagatov N., Sagatova D., Gavryushkin P. and Litasov K. Fe–N System at High Pressures and Its Relevance to the Earth’s Core Composition // ACS Publications. – 2021. – Vol. 21. – P. 6101–6109.

2. Sun Y., Mendelev M., Zhang F., Ho K. Unveiling the effect of Ni on the formation and structure of Earth’s inner core // Earth, atmospheric, and planetary science. – 2024. – Vol. 121. – P. 121.

3. Thompson S. and others. High-pressure melting experiments of Fe3S and a thermodynamic model of the Fe–S liquids for the Earth’s core // Journal of Physics: Condensed Matter. – 2022. – Vol. 34. – Iss. 39. – P. 394003. https://doi.org/10.1088/1361-648X/ac8263

4. Beyer C. and others. High-pressure phase relations in the system Fe–Ni–Cu–S up to 14 GPa: implications for the stability of sulfides in the Earth’s upper mantle. Mineralogy and Petrology. – 2022. – Vol. 177. – P. 1966.

5. Fei Y. et al. Structure type and bulk modulus of Fe3S, a new iron-sulfur compound // American Mineralogist. – 2000. – Vol. 85. – P. 1830–1833.

6. Zurkowski C. Fe5S2 identified as a host of sulfur in Earth and planetary cores // Earth and Planetary Science Letters. – 2022. – V. 593. – P. 117650.

7. Oka K. A cotunnite-type new high-pressure phase of Fe2S // American Mineralogist. – 2022. – Vol. 107. – P. 7959.

8. Bazhanova Z., Roizen V., OganovA. High-pressure behavior of the Fe–S system and composition of the Earth's inner core // Physics-Uspekhi. – 2017. – Vol. 60. – P. 1025–1032.

9. Tateno S. et al. Fe2S: The Most Fe-Rich Iron Sulfide at the Earth's Inner Core Pressures // Geophysical Research Letters. – 2019. – Vol. 46. – P. 11944–11949.

10. Urakawa S. Stability and bulk modulus of Ni3S, a new nickel sulfur compound, and the melting relations of the system Ni-NiS up to 10 GPa // American Mineralogist. – 2011. – Vol. 96. – P. 3578.

11. Prewitt C., Gramsch S., Fei Y. High-pressure crystal chemistry of nickel sulphides // Journal of Physics: Condensed Matter. – 2002. – Vol. 14. –P. 11411–11415.

12. Yu Y., Ross N. Vibrational and thermodynamic properties of Ni3S2 polymorphs from first-principles calculations // Physics and Chemistry of Minerals. – 2011. – Vol. 38. – P. 241–249.

13. Znahg Q. and others. First-Principles Study of the Elastic Properties of Nickel Sulfide Minerals under High Pressure // MDPI Minerals. – 2020. – Vol. 10. – P. 737.

14. Kresse G., Furthmuller J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set // Physical review B. – 1996.– Vol. 54. – P. 11169–11186.

15. Oganov A., Lyakhov A., Valle M. How evolutionary crystal structure prediction works – and why // Accounts of Chemical Research. – 2011. – Vol. 44. – P. 227–237.

16. Monkhorst H., Pack J. Special points for Brillouin-zone integrations // Physical review B. – 1976. – Vol. 13. – P. 5188–5192.

17. Methfessel M., Paxton A. High-precision sampling for Brillouin-zone integration in metals // Physical Review B. – 1989. – Vol. 40. – P. 3616–3621.

18. McMahan A., Albers R. Insulating Nickel at a Pressure of 34 TPa // Physical Review Letters. – 1982. – Vol. 49. – P. 1198–1201.

19. Zakharov O., Cohen M. Theory of structural, electronic, vibrational, and superconducting properties of highpressure phases of sulfur // Physical Review B. – 1995. – Vol. 52. – P. 12572–12578.

20. Rudin S., Liu A. Predicted simple-cubic phase and superconducting properties for compressed sulfur // Physical review letters. – 1999. – Vol. 83. – P. 3049–3052.

21. Rubin A., Ma C. Meteoritic minerals and their origins // Geochemistry. – 2017. – Vol. 77. – P. 325–385.

22. Sagatov E., Bazarbek A., Inerbaev T. et al. Phase Relations in the Ni−S System at High Pressures from ab InitioComputations // ACS Earth and Space Chemistry. – 2021. – Vol. 5. – P. 596–603.