Fast Li ionic conduction in solid solutions of the system Li4GeO4-Li2ZnGeO4-Li3PO4

A wide range of solid solution formation in the Li4GeO4-Li2ZnGeO4-Li3PO4 system was observed to occur with a structure based on γII-Li3PO4. This includes the fast Li conductor lisicon (Li14Zn(GeO4)4). The ionic conductivities of solid solutions in this systems are reported. Much of the solid solution range is structually metastable at room temperature; however, the decomposition kinetics are appreciable only at elevated temperatures (>350°C). The evolution of low Li4GeO4 on decomposing causes an irreversible decrease in the conductivity. At 200°C, the bulk ionic conductivity of several of these solid solutions is higher than that of lisicon. Solid solutions along the Li4GeO4-Li3PO4 tie line are structurally stable and have a higher bulk ionic conductivity than lisicon, and also of the corresponding Li4SiO4-Li3PO4 solid solutions at 200°C