Soft-chemistry of garnet-type Li_{5+ x}Ba_xLa _3-xNb₂O₁₂ (x = 0, 0.5, 1): Reversible H ⁺ ↔ Li⁺ ion-exchange reaction and their X-ray, ⁷Li MAS NMR, IR, and AC impedance spectroscopy characterization

Garnet-type Li_5+xBa_xLa_3-xNb ₂O₁₂ (x = 0, 0.5, 1) was prepared using the ceramic method. The H⁺/Li⁺ exchange was found to be most successful for x = 0, with ∼89% exchange, while x = 0.5 showed ∼46% exchange, and x = 1 showed ∼20% exchange in water at room temperature. For Li₅La₃Nb₂O₁₂, where more of the Li ions occupy tetrahedral sites (ca. 80%), the H⁺/Li⁺ exchange occurs readily. The population of octahedral-site Li ions increases as the amount of Li in Li_5+xBa_xLa_3-xNb ₂O₁₂ increases and the ion-exchange proceeds to a lesser extent in water at room temperature. The Li⁺/H⁺ ion-exchange of the proton-based garnet was found to be reversible, using 5 M LiNO₃. The electrical conductivity of as-prepared Li _5+xBa_xLa_3-xNb₂O₁₂, the proton-exchanged product, and reverse-ion-exchanged "Li₅La ₃Nb₂O₁₂" were measured using AC impedance spectroscopy. The Li-ion conductivities of the reverse-ion-exchanged and as-prepared Li₅La₃Nb₂O₁₂ were found to exhibit comparable values and are consistent with literature reports. The proton-exchanged sample showed a moderate electrical conductivity of <10 ^-6 S cm^-1 at 125-250 °C, which may be attributed to the poor density of samples.