Ion transport and diffusion in nanocrystalline and glassy ceramics

In the present paper we review experimental studies on ion transport and diffusion in nanocrystalline and glassy ceramics of LiNbO3 and LiAlSi2O6 and report on new ones on LiBO2 using the measurement of dc conductivities and Li-7 nuclear magnetic resonance spin-lattice relaxation rates. Nanocrystalline ceramics, with an average particle size of 50 enm and less, often show an enhanced diffusivity compared to their microcrystalline (mu m-sized) counterparts. This increase is due to the large fraction of atoms or ions located in the interfacial regions. A key for understanding the structure-mobility relations in nanocrystalline ceramics is to clarify the microscopic structure of the grain boundaries and also the morphology of the grain boundary network. In this context it is useful to study not only the ion transport properties of the nano- and microcrystalline materials but also those of the corresponding glassy forms. Such comparative studies gave strong evidence that in some cases the interfacial regions are of amorphous structure. For example, this was recently shown for nanocrystalline lithium niobate which was prepared by high-energy ball milling.