These two regimes (single crystal and fully amorphous), which are straightforward to simulate, are not representative of the realistic microstructure in glassceramic LPS electrolytes . All of the glass ceramic materials that are critical for building the next generation of all solid state batteries such as LISCION, LIPON, LGPS, and LPS lie within this range between fully amorphous to fully crystalline Li-ion conductors with hypothetical ⌧ SAE decay constants schematically depicted in Figure . That is, they are a mixture of glassy regions and crystalline regions (depicted as the Glass Ceramic and Polycrystalline in Figure ), in which the Li-ion conductivity across grain boundaries is often the determining factor for the quality of these super-ionic conductors. In these cases, we propose that SAE will provide a unique grain-boundary sensitive technique for understanding Liion diffusion, as the intra-grain diffusion will be at either the amorphous or crystalline limit, and therefore undetectable with SAE.