The short-range atomic structures of iron liquids alloyed with nickel and carbon have been investigated up to 7.3 GPa and 1773 K in a Paris-Edinburgh type large volume press. We found that the Fe-Ni (Fe90Ni10) liquids alloyed with 3 and 5 wt.% carbon underwent a liquid structural transition at approximately 5 gigapascals (GPa). First-principles molecular dynamics (MD) simulations were also conducted to decipher the nature of the liquid structure and the polyamorphic transition. Corroborating the experimental results, our calculations demonstrate that the high-pressure phase of the liquids is featured with the favoring of the 3-atom face-sharing connection schemes of atomic packing motifs. The structure change may significantly affect the properties of the Fe-Ni-C liquids. As such, it is likely the origin for the distinct geochemical imprints (i.e., iron and carbon isotopes) left behind by the formation of the core in Earth, in comparison with other terrestrial planets or planetary bodies (i.e., Mars and Vesta) and primitive undifferentiated meteorites (chondrites). The knowledge of the polyamorphic transitions in core-forming liquid iron alloys is crucial for our understanding of the chemical evolution of terrestrial bodies.
Lai, X., Chen, B., Wang, J., Kono, Y., & Zhu, F. (2017). Polyamorphic Transformations in Fe‐Ni‐C Liquids: Implications for Chemical Evolution of Terrestrial Planets. Journal of Geophysical Research: Solid Earth, 285(1327), 23. doi:10.1002/2017JB014835
