Phase transition of MnF2 driven by shock compression at pressure of up to 33 GPa

Rutile-type MnF2 was shock loaded at pressures of 3.6-33.4 GPa by the impact of flyer plates accelerated by a propellant gun. Recovered samples were examined by x-ray powder diffraction analysis and transmission electron microscopy (TEM). A phase transition from the rutile-type structure to the alpha-PbO2-type structure was found above 3.6 GPa. The yield of the alpha-PbO2 phase in the recovered samples increased for pressures of up to about 10 GPa and decreased at higher pressures. This phenomenon can be explained by a residual temperature effect. A lamellar pattern consisting of two crystalline phases (rutile and alpha-PbO2-type MnF2) was observed in the shocked sample by TEM observation. The shock-induced phase transition from the rutile-type structure to the alpha-PbO2-type structure was inferred to proceed via fluorite-related structures or a PbCl2-type structure by comparison with results of previous static high-pressure experiments.