Anion diffusivity in highly conductive nanocrystalline BaF2:CaF2 composites prepared by high-energy ball milling

We report on the fluorine diffusivity in nanocrystalline BaF2 and CaF2 as well as in BaF2:CaF2 composites prepared by high-energy ball milling. Mechanical treatment of polycrystalline BaF2 together with CaF2 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 19F 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)F2 phase.