High pressure phase transformation in FeF⊂2 (Rutile)

The structural relationships in FeF 2 have been studied under pressure up to 320 kbar and 25°C by use of the diamond anvil pressure cell. In situ X‐ray diffraction analysis shows that at about 50 kbar, FeF 2 (I) with rutile structure transforms into FeF 2 (II) of distorted fluorite structure and at about 250 kbar FeF 2 (II) further transforms into FeF 2 (III) with a hexagonal unit‐cell structure. The zero‐pressure density increase for the transition FeF 2 (I) → FeF 2 (II) is ∼ 8%, and the density increase for FeF 2 (II) → FeF 2 (III) at 320 kbar is ∼ 5%, if the number of formula units per unit cell is assigned at 2 for the hexagonal unit cell.