Sol Gel vs Solid State Synthesis of the Fast Lithium-Ion Conducting Solid State Electrolyte Li₇La₃Zr₂O₁₂Substituted with Iron

Two calcined products of Li 6.4 Fe 0.2 La 3 Zr 2 O 12 can be synthesized via the solid state method and the sol gel method. Inhomogeneities of the iron distribution in the powder for the solid state method lead to a combination of cubic and tetragonal structure. By using the sol gel method the homogeneity can significantly been increased resulting in the desired pure phase cubic structured powders in I 3 d . By in situ dilatometer measurements the densification process can be comprehended for the first time for garnet type materials. The density can be significantly increased by the usage of the sol gel synthesis compared to the solid state synthesis with short sintering times of 2 h delivering pure phase pellets for both synthesis methods. Electrical impedance measurements revealed clearly divided semicircles for the bulk and the grain boundary contribution for the solid state synthesis, while the sol gel synthesis showed only one semicircle from the bulk contribution due to a large crystallite size. The total ionic conductivity for the pellet synthesized via the sol gel method is 1.82 mS/cm at 25°C which is the fastest found so far for garnet type or garnet related materials.