Ultraslow Diffusion in Polycrystalline h-LiTiS_2 Studied by ~7Li Spin-Alignment Echo NMR Spectroscopy

摘要

Multiple-time spin-alignment echo (SAE) NMR spectroscopy of spin-3/2 nuclei is used to study ultraslow diffusion in the hexagonal layered Li ion conductor Li_xTiS_2 (x ≈ 1). Two-time correlation functions were monitored by recording (Jeener-Broekaert) echo amplitudes for constant evolution and variable mixing times. Echo decay rates τ_(SAE)~(-1), being directly related to Li jump rates, take values ranging from 2 s~(-1) to 570 s~(-1) between temperatures T = 185 K and 293 K. The temperature dependence of τ_(SAE)~(-1) shows Arrhenius behaviour with an activation energy of 0.26(1) eV, being similar to that obtained by spin-lattice relaxation measurements in the rotating as well as in the laboratory frame at higher temperatures.