Sol-gel synthesis and lithium ion conductivity of Li7La3Zr2O12 with Garnet-related type structures

Lithium ion conducting garnet-related type Li7La3Zr2O12 (LLZO) nanopowders were prepared by the modified sol–gel Pechini method from the stoichiometric mixtures of lithium carbonate, lanthanum oxide and zirconium ethoxide. The LLZO precursor powders were annealed at various temperatures between 923 and 1173 K for 5 h in air atmosphere. The products were characterized by thermal analysis (TG/DTA) and X-ray powder diffraction (XRPD) to verify the transformation from precursor powder to crystalline garnet-related phase. XRPD analysis shows that cubic phase of garnet-related type Li7La3Zr2O12 is formed at 978 K and the tetragonal garnet-related phase above 997 K. The morphology of the particles was investigated by Scanning Electron Microscopy (SEM). The lithium ionic conductivity of the tetragonal Li7La3Zr2O12 sample prepared by sol–gel synthesis method is found to be 3.12 × 10- 7 S/cm at 298 K while the corresponding activation energy is 0.67 eV. The results of the ionic conductivities are in good agreement with those of the tetragonal LLZO synthesized by conventional solid-state synthesis method.