Anion diffusivity in highly conductive nanocrystalline BaF(2):CaF(2) composites prepared by high-energy ball milling

We report on the fluorine diffusivity in nanocrystalline BaF(2) and CaF(2) as well as in BaF(2):CaF(2) composites prepared by high-energy ball milling. Mechanical treatment of polycrystalline BaF(2) together with CaF(2) results in a nanocrystalline composite with an unexpectedly high dc conductivity of about 0.1 mS cm(-1) at 450 K. X-ray diffraction and (19)F magic angle spinning NMR measurements at extraordinary high spinning speeds reveal that this can be explained inter alia by the interplay of structural disorder and the formation of a mixed (Ba,Ca)F(2) phase.