Macroscopic and microscopic Li+ transport parameters in cubic garnet-type Li6.5La2.5Ba0.5ZrTaO12 as probed by impedance spectroscopy and NMR

The garnet-type Li6.5La2.5Ba0.5ZrTaO12, 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 Li6.5La2.5Ba0.5ZrTaO12. Li ion dynamics were complementarily studied using variable-temperature AC-impedance spectroscopy and Li-7 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 Li6.5La2.5Ba0.5ZrTaO12. 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 Li6.5La2.5Ba0.5ZrTaO12 was tested with Li2FeMn3O8, 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.