Ab Initio Superionic-Liquid Phase Diagram of Fe_{1-x}O_{x} under Earth's Inner Core Conditions.

Area of Science:

• Geophysics
• Materials Science
• Thermodynamics

Background:

• The superionic state, characterized by liquid-like ionic mobility within a solid lattice, has been identified in Earth's inner core (IC).
• Understanding the phase diagram of the iron-oxygen system under IC conditions is crucial for geophysical interpretations.
• Previous studies have largely unexplored the ab initio phase diagram of superionic and liquid states under core conditions.

Purpose of the Study:

• To compute the Gibbs free energy and construct the ab initio superionic-liquid phase diagram for the Fe_{1-x}O_{x} system under IC conditions.
• To investigate the influence of oxygen on the superionic state and iron diffusion within Earth's inner core.
• To establish a framework for studying superionic-liquid equilibria under extreme conditions.

Main Methods:

• A thermodynamic approach was utilized to calculate Gibbs free energy.
• Ab initio calculations were performed to construct the phase diagram.
• The Fe_{1-x}O_{x} system under inner core conditions was modeled.

Main Results:

• Oxygen forms superionic states in both hexagonal close-packed (hcp) and body-centered cubic (bcc) iron phases.
• The presence of superionic states significantly influences the cooperative diffusion of iron in the bcc lattice.
• The stability fields of these superionic phases are sensitive to oxygen stoichiometry.
• Superionic states suggest a higher oxygen concentration in the IC than previously estimated.

Conclusions:

• The study provides a novel thermodynamic framework for understanding superionic-liquid equilibria under extreme conditions.
• The findings have significant implications for the composition and dynamics of Earth's inner core.
• This research advances the understanding of matter phases under extreme pressure and temperature.