Structural transformations including melting and recrystallization during shock compression and release of germanium up to 45 GPa

Solid-solid and solid-liquid transformations were examined in Ge(100), using in situ x-ray diffraction measurements during uniaxial strain compression and release. For final stresses above 15.7 GPa, the Ge transformed to a highly textured tetragonal $\ensuremath{\beta}$-Sn phase. At 31.5 GPa and above, Ge transformed to the molten phase. Full stress release (uniaxial strain) from the $\ensuremath{\beta}$-Sn phase, from the melt boundary, and from the completely molten phase, resulted in reversion to an untextured cubic diamond (cd) phase. These findings demonstrate that the cd to $\ensuremath{\beta}$-Sn phase change is reversible, and that recrystallization from the liquid phase occurs on nanosecond timescales during release.