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

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 $\hat{I}\pm$-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.

11 pages, 4 figures, under review