Ultraslow diffusion in polycrystalllne h-LITIS₂ studied by ₇Li spln-alignment echo NMR spectroscopy

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_xTiS₂ (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 2s ^-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.