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

Abstract

The garnet-type “Li_6.5La_2.5Ba_0.5ZrTaO₁₂”, 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 “Li_6.5La_2.5Ba_0.5ZrTaO₁₂”. 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_0.5ZrTaO₁₂”. 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 “Li_6.5La_2.5Ba_0.5ZrTaO₁₂” 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.