Electronic Temperature-Driven Phase Stability and Structural Evolution of Iron at High Pressure

TL;DR

This study uses finite-temperature density functional theory to map phase diagrams of iron under high pressure, revealing temperature-driven solid-solid phase transitions influenced by electronic entropy.

Contribution

It provides the first detailed Gibbs free-energy phase diagrams for iron at high pressures and temperatures, highlighting electronic entropy as a key factor in phase stability.

Findings

Phase transition from hcp to bcc above 200 GPa driven by electronic temperature.

Predicted phase boundaries align with recent experimental observations.

Electronic entropy significantly influences iron's structural evolution under extreme conditions.

Abstract

We present Gibbs free-energy phase diagrams for compressed iron within a pressure range of 20 to 300 GPa and electronic temperature up to 3 eV obtained using finite-temperature density functional and density functional perturbation theories. Our results for bcc, fcc, and hcp phases predict solid-solid phase transitions in iron driven purely by electronic entropy and temperature. We found a phase transition from hcp to bcc at pressures above 200 GPa, which depends on the electronic temperature. An experimental observation of the stability of the bcc phase above 200 GPa by X-ray Free Electron Laser has recently been reported.