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MM: Fachverband Metall- und Materialphysik
MM 49: Topical Session Battery Materials I
MM 49.2: Topical Talk
Donnerstag, 25. März 2010, 10:45–11:15, H6
Ion conductivity and effects of mechanical treatment — •Paul Heitjans and Martin Wilkening — Institut für Physikalische Chemie und Elektrochemie, Leibniz Universität Hannover, D-30167 Hannover
A way to enhance the ionic conductivity of materials being suitable, e.g., for batteries is to reduce the crystallite size. The largely increased volume fraction of interfacial regions in nanocrystalline ceramics provides pathways for fast cation as well as anion diffusion. Nanostructuring can easily be achieved by high-energy ball milling. We will review studies on single- and two-phase ion conductors such as Li4Ti5O12, LiTaO3, LiNbO3 and Li2O:Al2O3, BaF2:CaF2, respectively, serving as model substances to investigate the effect of mechanical treatment on the ionic diffusivity. As an example, ball milled nanocrystalline LiTaO3 - even when treated in a shaker mill for only 30 min - exhibits an increase of the overall room temperature Li conductivity by about five orders of magnitude compared to that of the coarse grained source material. Mechanical treatment of BaF2 and CaF2 together for about 32 h in a shaker mill leads to a composite material where the anion conductivity is increased by a factor of 103 compared to that of single-phase nanocrystalline BaF2 prepared under the same conditions. Besides conductivity measurements we used a variety of 7Li and 19F solid state NMR techniques to gain detailed information about the dynamics as well as first insights into the microstructure of these highly defective materials.