Shock-driven amorphization and melt in Fe$_2$O$_3$

TL;DR

This study investigates the shock-induced amorphization and melting of Fe₂O₃ using in situ x-ray diffraction and theoretical calculations, revealing phase transitions and amorphous states at high pressures up to 209 GPa.

Contribution

It reports the first direct observation of shock-induced amorphization of Fe₂O₃ and characterizes the phase transitions and melt behavior under extreme conditions.

Findings

Amorphization occurs between 122 and 145 GPa.

A phase change is indicated by peak intensity ratio shifts between 145 and 151 GPa.

The melt state resembles ambient-pressure Fe₂O₃ melt in structure.

Abstract

We present measurements on Fe$_2$O$_3$ amorphization and melt under laser-driven shock compression up to 209(10) GPa via time-resolved in situ x-ray diffraction. At 122(3) GPa, a diffuse signal is observed indicating the presence of a non-crystalline phase. Structure factors have been extracted up to 182(6) GPa showing the presence of two well-defined peaks. A rapid change in the intensity ratio of the two peaks is identified between 145(10) and 151(10) GPa, indicative of a phase change. Present DFT+$U$ calculations of temperatures along Fe$_2$O$_3$ Hugoniot are in agreement with SESAME 7440 and indicate relatively low temperatures, below 2000 K, up to 150 GPa. The non-crystalline diffuse scattering is thus consistent with the - as yet unreported - shock amorphization of Fe$_2$O$_3$ between 122(3) and 145(10) GPa, followed by an amorphous-to-liquid transition above 151(10) GPa. Upon release, a non-crystalline phase is observed alongside crystalline $\alpha$-Fe$_2$O$_3$. The extracted structure factor and pair distribution function of this release phase resemble those reported for Fe$_2$O$_3$ melt at ambient pressure.