Thermal Induced Structural Competitiveness and Metastability of Body-centered Cubic Iron under Non-Equilibrium Conditions

TL;DR

This study uses ab initio calculations to reveal how high electron temperatures stabilize the body-centered cubic phase of iron, making it metastable and competitive with other phases under extreme conditions relevant to Earth's core.

Contribution

The paper demonstrates that elevated electron temperatures induce metastability and structural competitiveness of BCC iron, providing new insights into its phase behavior under non-equilibrium high-pressure conditions.

Findings

BCC phase stabilized at high electron temperatures (>1-1.5 eV)

Emergence of a potential energy plateau and local minimum in BCC iron

Enhanced thermodynamic stability due to lattice vibration entropy

Abstract

The structure and stability of iron near melting at multi-megabar pressures are of significant interest in high pressure physics and earth and planetary sciences. While the body-centered cubic (BCC) phase is generally recognized as unstable at lower temperatures, its stability relative to the hexagonal close-packed (HCP) phase at high temperatures (approximately 0.5 eV) in the Earth's inner core (IC) remains a topic of ongoing theoretical and experimental debate. Our ab initio calculations show a significant drop in energy, the emergence of a plateau and a local minimum in the potential energy surface, and stabilization of all phonon modes at elevated electron temperatures (>1-1.5 eV). These effects increase the competition among the BCC, HCP, and the face-centered cubic (FCC) phases and lead to the metastability of the BCC structure. Furthermore, the thermodynamic stability of BCC iron is enhanced by its substantial lattice vibration entropy. This thermally induced structural competitiveness and metastability under non-equilibrium conditions provide a clear theoretical framework for understanding iron phase relations and solidification processes, both experimentally and in the IC.