Germanium

Interestingly, phase transformations were found to dominate the deformation mechanisms of Si but not of the structurally-similar material, Ge. Instead, XTEM and Raman spectroscopy showed that, in Ge, plastic deformation at room temperature occurred predominantly by twinning and dislocation motion.  This indicates that the hardness of Ge is not necessarily dominated by a phase transformation.

Bright-field (left) and dark-field (right) transmission electron microscopy images of spherical indents in crystalline Ge. Clearly shows twinning as a deformation mechanism.