Herein, two fast Li + conductors were studied specifically to investigate isotopic effects that transcend structure type. Both materials were synthesized as enriched compounds with the two isotopes Li and Li in order to compare the composition 6 Li10SnP2S12 to 7 Li10SnP2S12 as well as Li6PS5Cl to 7 Li6PS5Cl. The isotopic purity of lithium is >95% for all compositions ( 7 Li > 99%, Li > 95%). Compared to samples synthesized from the natural isotope abundance (~7% Li and ~93% Li), our enriched Li compounds allow for direct investigations of differences in ionic transport between the two isotopes. Information on the synthesis procedure and the laboratory Xray diffraction data can be found in the Supporting Information (Supplemental Note 1).