Soft-Chemistry of Garnet-Type Li5+xBaxLa3-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 Li5+xBaxLa3-xNb2O12 (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 similar to 89% exchange, while x = 0.5 showed similar to 46% exchange, and x = 1 showed similar to 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 Li5+xBaxLa3-xNb2O12 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 Li5+xBaxLa3-xNb2O12, the proton-exchanged product, and reverse-ion-exchanged Li5La3Nb2O12 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 degrees C, which may be attributed to the poor density of samples.