Phase transitions of Fe$_2$O$_3$ under laser shock compression

TL;DR

This study investigates the high-pressure phase transitions of Fe$_2$O$_3$ under laser shock compression, revealing a new phase and a spin transition not seen in static studies, with implications for understanding its behavior under extreme conditions.

Contribution

The paper reports the discovery of a new $ extit{ extprime}$-Fe$_2$O$_3$ phase and associated spin transition during laser shock compression, contrasting static compression results.

Findings

Observation of a new $ extit{ extprime}$-Fe$_2$O$_3$ phase at 50-62 GPa

Detection of an isostructural phase transition with volume drop

Identification of a spin transition linked to magnetic collapse

Abstract

We present in-situ x-ray diffraction and velocity measurements of Fe$_2$O$_3$ under laser shock compression at pressures between 38-116 GPa. None of the phases reported by static compression studies were observed. Instead, we observed an isostructural phase transition from $\alpha$-Fe$_2$O$_3$ to a new $\alpha^\prime$-Fe$_2$O$_3$ phase at a pressure of 50-62 GPa. The $\alpha^\prime$-Fe$_2$O$_3$ phase differs from $\alpha$-Fe$_2$O$_3$ by an 11% volume drop and a different unit cell compressibility. We further observed a two-wave structure in the velocity profile, which can be related to an intermediate regime where both $\alpha$ and $\alpha^\prime$ phases coexist. Density functional theory calculations with a Hubbard parameter indicate that the observed unit cell volume drop can be associated with a spin transition following a magnetic collapse.