Figure shows exemplarily the Nyquist plots of the room-temperature EIS measurements for all spinel compounds with a pellet mass of 160 mg in the sandwich-type cells. An overview of all Nyquist plots obtained over the complete temperature range between 0-60 °C for at least three different layer thicknesses/masses per spinel are depicted in the Supporting Information (Figures ). Based on the fitted Nyquist plots the average conductivity per spinel at room-temperature and 60 °C was determined. As shown in Figure , the newly examined MgB2Se4 spinels have a similarly high ionic conductivity as MgSc2Se4