The long- and short-range motions of Li ions into electrochemically intercalated sintered pellets of Li3xLa2/3-xTiO3 were studied by means of alternating-current impedance spectroscopy and 7Li solid-state nuclear magnetic resonance techniques. The temperature dependence of the direct-current conductivity and the intercalation-ratio dependence of the chemical shift, the relative intensity of the resonance line, and the spin-lattice and spin-spin relaxation times of 7Li nuclear magnetic resonance data indicated polaron formation in the initial stages of intercalation. The total direct-current conductivity between 45 and 600K, and the shape of the impedance diagrams, showed that - after intercalation - the conductivity was both ionic and electronic in nature. At temperatures below 300K, the overall conductivity was dominated mainly by the electronic contribution. At temperatures above 400K, the overall conductivity was dominated by the ionic component. The nuclear magnetic resonance data clearly showed that the resonance peak decreased markedly during intercalation. This was attributed to a coupling between the electronic and the Li+ nuclear spins; leading to a non-observability of some Li+ nuclei in nuclear magnetic resonance. The other Li+ nuclei, which did not interact directly with the electronic spins, were responsible for the observed nuclear magnetic resonance signal. If the static effect of the intercalation was weak, and led to a very small chemical-shift variation, variable-temperature 7Li nuclear magnetic resonance spin-lattice and spin-spin relaxation measurements showed that the presence of electrons acted essentially upon the dynamics of the Li+ nuclei, via the lattice modification which was induced by polaron formation. At the beginning of intercalation, the reciprocal of the relaxation time of the observed Li+ nuclei decreased by an order of magnitude. At the same time, the linewidth of the resonance peak suddenly decreased. The motion of the Li ions increased sharply. Upon further intercalation, the reciprocal of the relaxation time decreased and the linewidth of the central peak increased; thus indicating that variations in the relaxation times were governed mainly by variations in the spectral densities of the Li+ motion. Therefore, Li motion decreased gradually as intercalation proceeded. The results were in good agreement with a lattice modification that was due to polaron formation during intercalation.

Polaronic Effects on Lithium Motion in Intercalated Perovskite Lithium Lanthanum Titanate Observed by 7Li NMR and Impedance Spectroscopy. J.Emery, O.Bohnke, J.L.Fourquet, J.Y.Buzaré, P.Florian, D.Massiot: Journal of Physics - Condensed Matter, 1999, 11[50], 10401-17