7Li spin-alignment nuclear magnetic resonance was used to trace ultra-slow diffusion of Li+ in the layered Li conductor LixTiS2 (x = 0.7). Two-time correlation functions were recorded for fixed evolution times as a function of mixing time at temperatures within the 7Li rigid-lattice regime. The corresponding decay rates were identified as Li jump rates τ−1 ranging from 10−1 to 103/s between 148 and 213K. The jump rates obtained directly from spin-alignment echo nuclear magnetic resonance and those from diffusion induced maxima of spin-lattice relaxation peaks, monitored in the laboratory as well as in the rotating frame, were consistent with each other and follow an Arrhenius law with an activation energy of 0.41eV and a pre-exponential factor of 6.3 x 1012/s. Altogether, a solitary Li diffusion process was found between 148 and 510K. Li diffusion was investigated in a dynamic range of about 10 orders of magnitude, i.e., 0.1 ≤ τ−1 ≤ 7.8 x 108/s. Additionally, the analysis of final-state echo amplitudes of the two-time correlation functions revealed information about the Li diffusion pathway in Li0.7TiS2. Obviously, a two-site jump process was present, i.e., besides the regularly occupied octahedral sites also the vacant tetrahedral ones within the van der Waals gap were involved in the overall two-dimensional diffusion process.

Li Jump Process in h-Li0.7TiS2 Studied by Two-Time 7Li Spin-Alignment Echo NMR and Comparison with Results on Two-Dimensional Diffusion from Nuclear Magnetic Relaxation. M.Wilkening, P.Heitjans: Physical Review B, 2008, 77[2], 024311 (13pp)