${\mathrm{XeF}}_6\left(s\right)$ can be prepared by:

Taking $\mathrm{Xe}$ in excess at atmospheric pressure (1 bar) and temperature (673 K)

$\mathrm{Xe}:{\mathrm{F}}_2$  in 1:5 mole ration and pressure (7 bar) and temperature 873 K

$\mathrm{Xe}:{\mathrm{F}}_2$ in 1:20 mole ratio and high pressure (60-70 bar)and temperature 573 K

From product of (b), followed by an interaction with ${\mathrm{O}}_2{\mathrm{F}}_2 143\mathrm{K}$