Lithium dynamics in the fast ionic conductor Li0.18La0.61TiO3 probed by 7Li NMR spectroscopy -: art. no. 094301

Lithium dynamics in the Li0.18La0.61TiO3 perovskite quenched from 1623 K has been analyzed by means of Li-7 Nuclear magnetic resonance (NMR) spectroscopy and neutron powder diffraction. The Rietveld analysis of the diffraction pattern shows rhombohedral symmetry with lithium ions occupying square windows that connect contiguous A sites of the perovskite. The hopping of lithium ions through these windows produces the line narrowing detected above 170 K in Li-7 NMR spectra. Deconvolution of NMR spectra shows the existence of two lithium species that exchange their positions along the temperature range 250-350 K. In this temperature range, a plateau is detected in T-2(-1) plots, which has been ascribed to the existence of two-dimensional motions of lithium in ordered domains of the perovskite. Evidence of this limited motion comes from the frequency dependence of the spin-lattice relaxation rates measured at the high temperature side of the asymmetric 1/T-1 maximum (omegataumuch less than1 regime). T-1rho measurements indicate that there is a slower motion of lithium with a characteristic time of 3x10(-6) s at room temperature, assigned to isotropic three-dimensional diffusion.