Nuclear magnetic resonance investigation of Li+ -ion dynamics in the perovskite fast-ion conductor Li3xLa2/3-x□1/3-2xTiO3

Li-7 nuclear magnetic resonance relaxation times T-1, T-1rho and T-2 versus temperature are reported in the 150-900 K temperature range for the lithium lanthanum titanate Li(3)La(2/3-x)square(1/3-2x)TiO(3) perovskite-type fast-ionic conductors. The presence of Li+ ions of two kinds with slightly differing environments is displayed in these experiments. These ions exhibit two different motions: a fast one with a characteristic frequency around 100 MHz at 350 K and a slow one whose frequency is around 60 kHz at 280 K. These two different Li+ species cannot be differentiated by means of the fast motion (only one T, is observed from the experiments), but only by means of the slow ones (two T-1rho and two T-2 are observed). These motions are respectively attributed to Li+ motion inside the A-cage of the perovskite structure formed by the oxygen ions and to Li+ hops between the cages. T-1- and T-1rho-studies also performed on the Li-6 nucleus clearly show that just dipolar nuclear interaction is responsible for Li+ relaxation. This result is at variance with what has been previously put forward for the relaxation process in these compounds.