The proton/lithium exchange property of the lithium lanthanum titanate Li(0.30)La(0.57)TiO(3) (named LLTO) is shown to occur at room temperature under ambient air. The (1)H and (7)Li MAS NMR, TGA analysis and IR spectroscopy techniques are used to probe reaction mechanisms. XRPD analysis gives evidence of the topotactic character of this exchange reaction. As for exchange in aqueous solution, it is shown that Li(0.30)La(0.57)TiO(3) is able to dissociate water on the grain surface and then to exchange H(+) for Li(+) into the perovskite structure. Lithium hydroxide is then formed on the grain surface and afterwards reacts with CO(2) contained in air to form Li(2)CO(3). It is shown that this mechanism is reversible. When the aged sample (aging in air for 5 months at room temperature) is annealed at 400 degrees C for two hours, the initial LLTO sample is totally recovered, a mass loss is observed and the carbonate signal in IR spectra disappears, demonstrating the reversibility of the carbonation reaction process.
The property of the lithium lanthanum titanate (Li 3x La 2/3-x 0 1/3-2x )TiO 3 (or LLTO) to exchange protons for lithium has been used to prepare exchanged titanates and indirectly localize Li in the perovskite structure. The exchange reaction has been carried out in ultrapure water to follow the rate of exchange by measuring the pH of the solution. This study shows that a topotactic exchange reaction takes place in LLTO powder that leads to a novel perovskite phase where lithium ions are partially substituted by protons. The rate of exchange depends on the exchange reaction temperature. In the oxide with a high rate of exchange, three types of protons with different environments are clearly detected by 1 H MAS NMR. According to the crystallographic structure of LLTO and to the different basic character of these protons linked to oxygen, it has been possible to propose a location of each type of protons in the structure. The protons are mainly linked to oxygen O3 and to oxygen O2 in the structure and in a very small proportion to oxygen O1. To observe correlation between 1 H nuclei, homonuclear dipolar recoupling BABA and exchange sequence were used. Finally, if we assume that in the exchanged oxides the protons have the same location as the Li + ions in LLTO, it is then possible to propose a location of these Li + ions and to give an interpretation of the 7 Li NMR spectra.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.