High lithium ion conductivity of Li7La3Zr2O12 synthesized by solid state reaction

• Li+ conductivity of 0.49 mS cm-1 at 25 °C has been attained in Li7La3Zr2O12.
• The origin of improvement in Li+ conductivity was investigated.
• The location of Al3+ was verified by diverse structural analysis techniques.

A lithium ion conductor with the garnet-type structure, Li7La3Zr2O12 (LLZ), showing a high Li+ conductivity of 0.49 mS cm− 1 at 25 °C, is synthesized via milling (500 rpm, 12 h) and following sintering at 1125 °C for 20 h. The improved Li+ conductivity is attributed to the decrease of the particle size, the uniform distribution of particles before sintering, the high concentration of Li+ in the octahedral site (96h), and low occupancies of Li+ in the tetrahedral site (24d). Also, it is found that the cubic phase of LLZ is stabilized by a contamination of Al3 + ion into the LLZ lattice. The structural position of Al3 + is verified to be in the tetrahedral site (24d) by analyzing SEM images, MAS NMR, Pawley refinement using X-ray powder diffraction, and structural refinement using neutron powder diffraction data.