Electronic and structural properties of the high-pressure phase of ${\mathrm{Fe}}_2{\mathrm{O}}_3$ were determined by combining the methods of Mössbauer spectroscopy, x-ray diffraction, and electrical resistance, $R(P,T)$, to 80 GPa. Because of a first-order phase transition taking place in the 50–75 GPa range and accompanied by a volume decrease of $\sim 10\%$, a breakdown of the electronic $d-d$ correlation occurred, leading to a Mott transition, a metallic and a nonmagnetic single ${\mathrm{Fe}}^{3+}$ electronic state. The high-pressure structure is of the distorted ${\mathrm{Rh}}_2{\mathrm{O}}_3-\mathrm{II}$ type. The accommodation of the denser phase within this six-coordinated structure is attributable to the metallic state.

• Received 1 February 1999

DOI:https://doi.org/10.1103/PhysRevLett.82.4663