To measure the ionic conductivity with AC-impedance spectroscopy, the as-synthesized powders were cold-pressed into pellets. The ionic conductivity showed a maximum at x = 0.3 at 2.02 mS/cm, an increase by a factor ~1.6 compared to Li3InCl6 (1.52 mS/cm) (Figure ; See supplementary files for the data, equivalent circuit model and fitted parameter with errors; See SI Figure for the confirmation of validity of the equivalent circuits using the Kramers-Kronig relationship; See SI Table for error calculations). The maximum in ionic conductivity also corresponds with the lowest activation energy of 280 meV, though the differences in activation energy between the different compositions is small and not significant in most cases.