A study of the crystal structure of Fe₂O₃in the pressure range up to 65 GPa using synchrotron radiation

High-pressure X-ray powder diffraction has been performed on corundum-type αFe 2 O 3 (hematite) in the pressure range up to 65 GPa using synchrotron radiation and a diamond anvil cell. A structural phase transformation has been observed with a transition pressure of about 55 GPa. The high-pressure form of Fe 2 O 3 is orthorhombic. The lattice parameters at 60 GPa are a = 4.59(3) Å, b = 4.97(3) Å, c = 6.68(5) Å, Z = 4. The crystal structure is most probably a GdFeO 3 -type perovskite with space group Pbnm. The volume per formula unit in the orthorhombic phase is 10% smaller than in αFe 2 O 3 . It is suggested that the volume change is due to a combination of a valence change and a high-spin/low-spin transition. The bulk modulus, B 0 , and its pressure derivative, B' 0 , evaluated at zero pressure for αFe 2 O 3 are B 0 = 230(5) GPa and B' 0 = 3.5(6).