Abstract
High-pressure X-ray powder diffraction has been performed on corundum-type αFe2O3 (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 Fe2O3 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 GdFeO3-type perovskite with space group Pbnm. The volume per formula unit in the orthorhombic phase is 10% smaller than in αFe2O3. 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, B0, and its pressure derivative, B'0, evaluated at zero pressure for αFe2O3 are B0 = 230(5) GPa and B'0 = 3.5(6).
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