Li ION DYNAMICS IN ISOTOPE-DILUTED GLASSY Li2Si3O7 ― THE GENERATION OF PURE SPIN-3/2 JEENER-BROEKAERT NMR ECHOES
Dominik Wohlmuth,1 Viktor Epp,1 Ute Bauer,2 Anna-Maria Welsch,2 Harald Behrens2 and Martin Wilkening1
1Christian-Doppler Laboratory for Lithium Batteries, Graz University of Technology, Institute for Chemistry and Technology of Materials, Stremayrgasse 9, 8010 G
15:20 - 17:30 Thursday 24 October 2013 Foyer Alte Technik Solid-state diffusion plays one of the most important roles in materials science. In particular, the precise measurement of ion dynamics in materials with structural disorder is of great interest. Spin-alignment echo (SAE) nuclear magnetic resonance (NMR), being comparable to exchange spectroscopy, turned out to be a powerful method to probe (ultra-)slow Li dynamics even in amorphous materials [1,2]. However, 7Li Jeener-Broekaert echoes can be influenced by the simultaneous generation of dipolar with quadrupolar order. In many cases, the first can be suppressed by choosing proper evolution times tp of less than 20 µs [3].
Here, glassy Li2Si3O7 served as a suitable model system to study the positive influence of isotope dilution on 7Li SAE NMR, i.e., the reduction of homonuclear dipole-dipole interactions through spatial separation of the 7Li spins. Two samples, one with 100% 7Li and the other one with 5% 7Li (95% 6Li), were investigated by 7Li NMR line-shape analysis, spin-lattice relaxation NMR as well as mixing-time and pre¬paration-time dependent 7Li SAE NMR. Jeener-Broekaert echoes and their Fourier transforms show that at sufficiently short tp the interfering dipolar interactions can be completely suppressed in the sample where the proportion of 7Li was greatly reduced by substitution with 6Li. The so-obtained diffusion parameters are compared with results deduced from conductivity spectroscopy.
[1] V. Epp, C. Brüning, M. Binnewies, P. Heitjans, M. Wilkening, Z. Phys. Chem. 226 (2012) 513;
M. Wilkening, A. Kuhn, P. Heitjans, Phys. Rev. B 78 (2008) 054303.
[2] M. Wilkening, P. Heitjans, Chem. Phys. Chem. 13 (2012) 53.
[3] X.-P. Tang and Y. Wu, J. Magn. Res. 133 (1998) 155.
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