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

7Li nuclear magnetic resonance relaxation times T1, T1ρ and T2 versus temperature are reported in the 150-900 K temperature range for the lithium lanthanum titanate Li3xLa2/3-x□1/3-2xTiO3 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 T1 is observed from the experiments), but only by means of the slow ones (two T1ρ and two T2 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. T1- and T1ρ-studies also performed on the 6Li 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. (author)