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DF: Dielektrische Festkörper

DF 4: Poster

DF 4.16: Poster

Samstag, 5. März 2005, 08:30–16:30, Poster TU C

Investigation of Slow Li Diffusion in Amorphous Lithium Niobate by Multiple Time Spin-Alignment Echo NMR Spectroscopy — •Martin Wilkening and Paul Heitjans — Universität Hannover, Institut für Physikalische Chemie und Elektrochemie

Recently, three-dimensional Li diffusion in amorphous LiNbO₃ was investigated by temperature (140 K ≤ T ≤ 450 K) and frequency (23 MHz ≤ ω₀/2π ≤ 78 MHz) dependent spin-lattice relaxation NMR [1]. Measurements of the spin-lattice relaxation rate T₁⁻¹ had to be restricted to below 450 K in order to avoid crystallization of the sample. Thus, only the low-temperature flank of the diffusion induced peak of T₁⁻¹ was experimentally accessible yielding information about short-range Li diffusion. Long-range diffusion parameters below 450 K, however, can be probed, e. g., by multiple time stimulated-echo NMR spectroscopy, being sensitive to slow Li dynamics. Jump rates extracted from spin-alignment echo decays exhibit Arrhenius behaviour between 293 K and 413 K with an activation energy of 0.41(1) eV. This value is in good agreement with the activation energy of the not accessible high-temperature flank of the relaxation peak T₁⁻¹(1/T). The latter one was predicted to be about 0.4 eV [1] taking into account the frequency dependence of the diffusion induced spin-lattice relaxation rates on the low-T flank.

[1] M. Wilkening, D. Bork, S. Indris, and P. Heitjans, Phys. Chem. Chem. Phys. 4, 3246 (2002).