Dresden 2003 – scientific programme

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M: Metallphysik

M 36: Diffusion und Punktdefekte I

M 36.2: Talk

Thursday, March 27, 2003, 10:30–10:45, IFW B

⁷Li spin-alignment echo NMR spectroscopy: Detection of ultraslow motions in polycrystalline h-LiTiS₂ — •Martin Wilkening and Paul Heitjans — Institut für Physikalische Chemie und Elektrochemie, Universität Hannover, Germany.

Multidimensional alignment echo NMR spectroscopy of spin-3/2 nuclei [1, 2] is used to study ultraslow motions in the hexagonal layered Li ion conductor Li_xTiS₂ (x ≈ 1). Two-time correlation functions in the temperature regime 140 K – 280 K were monitored by recording (Jeener-Broekaert) echo amplitudes for variable mixing times t_m. For temperatures higher than 190 K the spin-alignment echo decay is dominated by slow translational jumps of Li ions hopping between different sites. The data can be fitted well with a stretched exponential function, resulting in translational jump rates τ⁻¹ with values ranging from 2 s⁻¹ to 200 s⁻¹. The temperature dependence of τ⁻¹ shows Arrhenius behaviour with an activation energy of 0.25 eV. This value is similar to that obtained by spin-lattice relaxation NMR measurements at higher temperatures [3].

[1] X.-P. Tang and Y. Wu, J. Magn. Reson. 133 (1998) 155–165.
[2] F. Qi, T. Jörg, R. Böhmer, Solid State Nucl. Magn. Reson. 22 (2002) 484–500.
[3] W. Küchler, P. Heitjans, A. Payer, R. Schöllhorn, Solid State Ionics 70/71 (1994) 434–438.