We investigate the high-pressure polymorphism of $\mathrm{Ti}{\mathrm{O}}_2$ under laser-shock compression from 54(5) to 137(7) GPa using in situ femtosecond x-ray diffraction. Our results provide experimental evidence of the $Pca{2}_1$-type distorted fluorite structure formed from polycrystalline $\mathrm{Ti}{\mathrm{O}}_2$ dynamically compressed to 54(5) GPa. Upon higher compression, we observe the direct formation of the ninefold coordinated $\mathrm{F}{\mathrm{e}}_2\mathrm{P}$-type phase at 68(4) and 78(3) GPa in polycrystalline and [001]-oriented $\mathrm{Ti}{\mathrm{O}}_2$, respectively. This represents an unprecedented 100 GPa reduction in the shock synthesis pressure of the $\mathrm{F}{\mathrm{e}}_2\mathrm{P}$-type structure relative to quasihydrostatic loading conditions. On pressure release, the $\mathrm{F}{\mathrm{e}}_2\mathrm{P}$-type phase transforms to the α-$\mathrm{Pb}{\mathrm{O}}_2$ structure and, at later times, reverts to rutile. Thus, the rutile $\to \mathrm{F}{\mathrm{e}}_2\mathrm{P}$ and α-$\mathrm{Pb}{\mathrm{O}}_2\to \mathrm{rutile}$ transformations are both observed to occur on nanosecond timescales. Our results highlight the unique ability of high-strain-rate uniaxial compression to synthesize novel high-pressure phases and also indicate the importance of in situ atomic-level probes in developing pressure-temperature phase diagrams.

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• Phase transitions
• Shock waves
• Crystal structures
• X-ray diffraction