Nanocrystalline materials could show enhanced diffusivity compared to their microcrystalline counterparts due to the large fraction of atoms or ions located in interfacial regions. In the case of ceramics, resulting properties with potential applications are, e.g., fast ionic conductivity, high mechanical creep rate and increased catalytic activity. Different nanocrystalline ceramic materials were prepared by high-energy ball milling of coarse grained source materials. The samples were characterized by XRD, TEM, BET method and IR spectroscopy. These measurements showed that the primary crystallites form larger agglomerates with internal interfaces and that the reduction of the crystallite size was accompanied by a structural degradation of the surface zone. An example was the partial amorphization observed for LiBO2 by IR spectroscopy. The diffusivity and ion conductivity in these materials was studied by NMR relaxation, NMR line shape and impedance spectroscopy. It was possible to discriminate between highly mobile ions in the interfacial regions and immobile ions in the grains. In general diffusion in the nanocrystalline systems was found to be fast compared to that in the corresponding microcrystalline source materials.

Fast Diffusion in Nanocrystalline Ceramics Prepared by Ball Milling. P.Heitjans, S.Indris: Journal of Materials Science, 2004, 39[16-17], 5091-6