Soft-Chemistry of Garnet-Type Li_5+xBa_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+ x Ba x La 3– x Nb 2 O 12 ( 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 Li 5 La 3 Nb 2 O 12, 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+ x Ba x La 3– x Nb 2 O 12 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 LiNO 3 . The electrical conductivity of as-prepared Li 5+ x Ba x La 3– x Nb 2 O 12, the proton-exchanged product, and reverse-ion-exchanged “Li 5 La 3 Nb 2 O 12 ” were measured using AC impedance spectroscopy. The Li-ion conductivities of the reverse-ion-exchanged and as-prepared Li 5 La 3 Nb 2 O 12 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.