Nanocrystalline state and solid state amorphization

The nanocrystalline state is reviewed in terms of various defect structures. In particular the role of disclination type defects has to be considered in order to understand quantitatively the atomic structures of nanocrystalline grain boundaries. Further it is stressed that atomic relaxation occurring in the boundaries can lead to different atomic structures. As a consequence, nanocrystallinity is often a desirable microstructural state for promoting the solid state amorphization reaction (SSAR). This possibility is examined in several systems including an illustration from our studies.