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

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.