Despite the formation of interphases related to the decomposition of LLZO the sole incorporation of a transition metal into the garnet structure could have significant structural and electrochemical consequences; studies in this respect are, however, absent. For example, the incorporation of Fe has been demonstrated to enable Li-ion conductivities up to 1.3 mS/cm; but the incorporation of 3d-electonic states can also cause electronic conduction. The later one could be beneficial when used as a catholyte, but detrimental when used as a separator.