Lithium garnet materials are promising candidates as inorganic solid state electrolytes for use in all solid state batteries, owing to their high ionic conductivity, wide electrochemical window and high safety. However, garnets suffer from energy demanding synthesis, rapid proton exchange and high interfacial resistance. Furthermore, even the most promising lithium garnet material (Ga(_x)Li(_{7-3x})La(_3)Zr(_2)O(_{12})) requires specialised handling and has not reached the conductivity of current solvent based electrolytes. In this work alternative dopant strategies into the lithium garnet system are investigated to unlock new approaches to solid state batteries.

Firstly, the flexibility of the Pr dopant was explored, with primary aims to increase the Li conductivity in Li(_5)La(_3)Nb(_2)O(_{12}) based systems. Here, Pr was doped onto the Nb and La site with Li(_{5+x})La(_3)Nb(_{2-x})Pr(_x)O({12}) and Li(_5)La(_{3-x})Pr(_x)Nb(_2)O(_{12}) prepared respectively. The Li(_5.8)La(_3)Nb(_{1.2})Pr0.8O12 system had a room temperature conductivity of 0.41 mS cm(^{-1}), the highest reported for a lithium garnet with