Phase transition ofMnF2driven by shock compression at pressure of up to33GPa

Abstract

Rutile-type $\mathrm{Mn}{\mathrm{F}}_{2}$ was shock loaded at pressures of $3.6--33.4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ 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 $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pb}{\mathrm{O}}_{2}$-type structure was found above $3.6\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The yield of the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pb}{\mathrm{O}}_{2}$ phase in the recovered samples increased for pressures of up to about $10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ 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 $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pb}{\mathrm{O}}_{2}$-type $\mathrm{Mn}{\mathrm{F}}_{2}$) was observed in the shocked sample by TEM observation. The shock-induced phase transition from the rutile-type structure to the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pb}{\mathrm{O}}_{2}$-type structure was inferred to proceed via fluorite-related structures or a $\mathrm{Pb}{\mathrm{Cl}}_{2}$-type structure by comparison with results of previous static high-pressure experiments.