Structure and dynamics of Fe phases under Earth's core conditions

 

1. Iron-rich FeO compounds: For a long time, it has been thought only oxygen-rich Fe-O compounds exist. Using crystal structure prediction, Yang and collaborators discovered novel iron-rich FeO compounds at Earth’s core conditions. Our work challenges the traditional view and suggests that oxygen should be a possible light element in the solid inner core. The existence of these oxygen-bearing phases could extend the deep oxygen cycling to the solid inner core, an entirely global oxygen cycle. (Yang Sun et al. “Iron-rich Fe-O compounds at Earth's core pressures”, submitted to Nature Geoscience.)
   
   Nucleation process of the Earth’s inner core: Recent attempts to explain how the inner core solidified were surprisingly unsuccessful and led to the so-called “nucleation paradox”: the supercooling necessary for the hcp-Fe nucleation could not be achieved during the time Earth exists. To address the paradox, Yang and coworkers demonstrated for the first time that molten iron could crystallize into hcp phase via a two-step nucleation process with an intermediate bcc phase under the Earth's core conditions. We computed detailed nucleation rates and found the bcc phase is tens of orders of magnitudes faster than the hcp phase at the inner core boundary condition. Our results also suggest the present inner core could have more than one layer with predominant hcp and bcc phases. (Yang Sun et al. “Two-step nucleation of the Earth's inner core”, under review, https://arxiv.org/abs/2105.07296 )