Macroscopic and microscopic Li ⁺ transport parameters in cubic garnet-type "li _6.5La _2.5Ba _0.5ZrTaO ₁₂" as probed by impedance spectroscopy and NMR

The garnet-type "Li _6.5La _2.5Ba _0.5ZrTaO ₁₂", crystallizing with cubic symmetry was prepared according to a conventional solid state synthesis method using metal oxides and salt precursors of high purity. The formation of the "single-phase" garnet-type structure was studied by powder X-ray diffraction (PXRD). Electron microprobe analysis (EMPA) coupled with a wavelength-dispersive spectrometer (WDS) showed a rather homogeneous distribution of Ta ions and Zr ions compared to that of Ba ions and La ions in "Li _6.5La _2.5Ba _0.5ZrTaO ₁₂". Li ion dynamics were complementarily studied using variable-temperature AC-impedance spectroscopy and ⁷Li NMR measurements. The bulk (ion) conductivities probed are in very good agreement with results reported earlier, illustrating the excellent reproducibility of the Li transport properties of "Li _6.5La _2.5Ba _0.5ZrTaO ₁₂". In particular, AC impedance and NMR results indicate that the Li transport process studied is of long-range nature. Finally, the chemical compatibility of the electrolyte "Li _6.5La _2.5Ba _0.5ZrTaO ₁₂" was tested with Li ₂FeMn ₃O ₈, being a high-voltage cathode material. As shown by variable-temperature PXRD measurements, the garnet-type structure (bulk) was found to be stable up to 673 K.