Interface structures in nanocrystalline materials

Grain boundary and triple-junction structures in nanocrystalline palladium and titanium thin films and in nanocrystalline thorium dioxide powder and sintered pellets have been studied. Amorphous packets with bright contrast are seen in many of the grain boundary junctions and are considered to form as a result of the relaxation of triple-junction disclinations. The varying degrees of relaxation of disclinations in nanocrystals lead to a variety of grain boundary structures and are also responsible for the random variation in their lattice parameters in the different nanocrystaninc grains. The nanocrystalline state has been suggested as being a desirable microstructural criterion for solid state amorphization. Further, it is to be pointed out that no special features which could be attributed to the nature of bonding in the two materials were seen in this study. (Author)