Ion conduction and dynamics in mechanosynthesized nanocrystalline BaLiF3

Highly pure nanocrystalline BaLiF3 (space group Pm3̄m, inverse perovskite structure) with a mean crystallite size of the order of 30 nm was mechanosynthesized from the binary fluorides LiF and BaF2. The source materials with μm-sized crystallites were treated in a planetary mill for several hours at ambient temperature. The product is characterized by X-ray diffraction and transmission electron microscopy. Its ionic conductivity was probed by solid state impedance spectroscopy. For comparison, a coarse-grained sample of BaLiF3 with a mean crystallite diameter in the μm range was synthesized by conventional high-temperature ceramic synthesis. The ionic conductivity (dc) of the mechanosynthesized nanocrystalline sample, which is characterized by a large fraction of interfacial regions, is by about three orders of magnitude (T = 570 K) larger than that of the conventionally prepared one. Preliminary temperature-variable 7Li NMR spectra provide first insights into the Li dynamics of the samples studied.