Soft-Chemistry of Garnet-Type Li_(5+x)Ba_xLa_(3-x)Nb2O_(12) (x = 0, 0.5,1): Reversible H~+ <-> Li~+ Ion-Exchange Reaction and Their X-ray, ~7Li MAS NMR, IR, and AC Impedance Spectroscopy Characterization

摘要

Garnet-type Li_(5+x)Ba_xLa_(3-x)Nb2O_(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 Li5Ba_xLa3Nb2O_(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_xLa_(3-x)Nb2O_(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 LiNO3. The electrical conductivity of as-prepared Li_(5+x)Ba_xLa_(3-x)Nb2O_(12), the proton-exchanged product, and reverse-ion-exchanged "Li_5La3Nb2O_(12)" were measured using AC impedance spectroscopy. The Li-ion conductivities of the reverse-ion-exchanged and as-prepared Li5La3Nb2O_(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~ at 125—250 °C, which may be attributed to the poor density of samples.