Isostructural Phase Transition of Fe2O3 under Laser Shock Compression

We present in situ x-ray diffraction and velocity measurements of Fe_{2}O_{3} under laser shock compression at pressures between 38-122 GPa. None of the high-pressure phases reported by static compression studies were observed. Instead, we observed an isostructural phase transition from α-Fe_{2}O_{3} to a new α^{'}-Fe_{2}O_{3} phase at a pressure of 50-62 GPa. The α^{'}-Fe_{2}O_{3} phase differs from α-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 α and α^{'} 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.