the aliovalent substitutions (e.g., Ta 5+ ) at Zr sites also enhance the ionic conductivity . An order of magnitude of conductivity is enhanced from Li 5 La 3 Ta 2 O 12 to Li 6 BaLa 2 Ta 2 O 12 where the Li ions are occupied in tetrahedral as well as octahedral sites . Thus, garnet-type materials are found to be promising fast ion conductors owing to their wide range of substitutions and the stability of their skeleton structure.