Extended point defects in crystalline materials: Ge and Si
  B diffusion measurements are used to probe the basic nature of self-interstitial 'point' defects in Ge. We find two distinct self-interstitial forms - a simple one with low entropy and a complex one with entropy ~30 k at the migration saddle point. The latter dominates diffusion at high temperature. We propose that its structure is similar to that of an amorphous pocket - we name it a 'morph'. Computational modelling suggests that morphs exist in both self-interstitial and vacancy-like forms, and are crucial for diffusion and defect dynamics in Ge, Si and probably many other crystalline solids. 
Nick E. B. Cowern, Sergei Simdyankin, Chihak Ahn, Nick S. Bennett,   Jonathan P. Goss, Jean-Michel Hartmann, Ardechir Pakfar...
cond-mat.mtrl-sci cond-mat.mes-hall