Phase transition of MnF$_2$ by shock compression up to 33 GPa

Shock-induced phase transition of MnF$_2$ with the rutile structure was investigated using gun method in the pressure range between 3 and 33 GPa. Recovered samples were examined using X-ray diffraction method and transmission electron microscope (TEM) observation. The $\alpha$-PbO$_2$-type phase was observed in the recovered samples, and its yield had a maximum at about 10 GPa. Lamella patterns consisting of the rutile-phase and the $\alpha$-PbO$_2$-type phase intergrowth texture were observed in the TEM images of the sample shock-loaded to 9 GPa. The crystallographic relationship between both phases can be expressed as (001){\scriptsize $\alpha$-PbO$_2$} $\|$ (-101) {\scriptsize rutile} and [110]{\scriptsize $\alpha$-PbO$_2$} $\|$ [111]{\scriptsize rutile} by TEM observation. This directional relationship is different from that of TiO$_2$ previously reported, suggesting that possibility of a new mechanism for the phase transition from the rutile-type to the $\alpha$-PbO$_2$-type through fluorite-related structure under high pressure.