A review was presented of case studies of diffusion in nanocrystalline ceramics having grain sizes ranging from 5 to 50nm. The experimental methods used were either tracer diffusion and conductivity methods which were sensitive to macroscopic transport, or nuclear magnetic resonance techniques which complemented the others by giving access to microscopic diffusion parameters such as atomic hopping rates and jump barrier heights. In every case, the diffusion properties of the samples (single-phase or composite) were dominated by their grain boundaries or interfacial regions, respectively. In principle, all of the experimental techniques permitted the discrimination of the contributions to diffusion which arose from crystalline grains and from interfacial regions. Corresponding examples were presented for secondary ion mass spectrometric and impedance measurements performed on O conductors. Nuclear magnetic resonance studies of various nanocrystalline Li-ion conductors revealed that two Li species having different diffusivities were present. A comparison with coarse-grained counterparts showed that the slower ions were located inside crystallites while the faster ones were located in structurally disordered interfacial regions. Investigations of composite materials revealed phenomena which could be explained by the percolation of fast diffusion pathways which were made up of the interfaces between the 2 components.

Diffusion and Ionic Conduction in Nanocrystalline Ceramics. P.Heitjans, S.Indris: Journal of Physics - Condensed Matter, 2003, 15[30], R1257-89