High pressure phase transformation in iron under fast compression

We observe kinetic features-velocity loops-at the alpha to epsilon phase transformation of iron, similar with the ones reported when water is frozen into its ice VII phase under comparable experimental conditions. By using a phase nucleation and growth kinetic model with pressure dependent phase interface velocity we find that the thermodynamic path followed by the sample is strongly dependent on the drive conditions and sample characteristics. The velocity loops become broader and shallower at slower compressions, while on faster time-scales, e.g., for laser drivers, the loops form at higher velocities and may eventually disappear.