High pressure phase transformations in MgF₂ (rutile)

Employing a diamond‐anvil pressure cell and a YAG laser as a heating source, phase relationships in polycrystalline MgF 2 (rutile) were investigated to ∼330 kbar at both room temperature (∼23°C), and high temperature (∼1300°C). In situ high pressure X‐ray diffraction data show that MgF 2 (I) of rutile structure transforms into MgF 2 (II) of a cubic structure at ∼300 kbar at room temperature, and at ∼190 kbar at high temperature (∼1300°C), resulting in a negative d P /d T slope for the univariant line between MgF 2 (I) and MgF 2 (II) in the P‐T phase diagram. The molar volume differences at room temperature between MgF 2 (I) and MgF 2 (II) at 190 kbar and 300 kbar are ∼8% and ∼5%, respectively.