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[摘要]：The property of the lithium lanthanum titanate (Li3xLa2/3-x square(1/3-2x))TiO3 (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 H-1 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 H-1 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 Li-7 NMR spectra. |
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