Study of the diffusion of lithium and sodium ions in solids under regardment of the dimensionality of the crystal lattice

Low-dimensional diffusion was investigated to improve the understanding of the fundamentals of ion movement in condensed matter. Different model systems with different dimensionality of cation migration pathways were investigated using solidstate nuclear magnetic resonance (NMR) spectroscopy and impedance spectroscopy. Both experimental methods made it possible to complementarily study both Li and Na mobility over a wide range of jump rates. Metallic lithium as a well-known model system for isotropic diffusion was investigated using ⁷Li field-cycling NMR. The spin-lattice relaxation (SLR) rates were separated into an electronic contribution and a diffusion-induced contribution. The Korringa product was calculated from the actual measurements. The main focus was the comparison of different theoretical models describing the Li motion in metallic lithium. The well-known model by Bloembergen, Purcell and Pound already reproduced the data well, but two models by Sholl improved the results taking into account the type of crystal lattice and jump correlation effects. A single-vacancy diffusion mechanism was observed, but a double-vacancy mechanism was not excluded as elevated temperatures near the melting point of lithium were not available. Li_0.7Nb₃S₄ is isostructural to Li_0.7Nb₃Se₄ which was reported as possible 1D Li ion conductor due to its channel structure. Thus, Li_0.7Nb₃S₄ was investigated as 1D model system using solid-state NMR spectroscopy. Multinuclear NMR spectroscopy gave insights into structural properties. Li dynamics was observed by several NMR methods over a wide temperature range. ⁷Li NMR motional narrowing led to an estimate of the activation energy for local Li hopping. ⁷Li NMR spin-alignment echo (SAE) was used for the determination of Li jump rates on a macroscopic scale. Possible dimensionality effects were investigated by ⁷Li NMR SLR. Out of the phase system Li₂O:TiO₂ two compounds with different dimensionalities determined by their crystal lattice were also studied by solid-state NMR and impedance spectroscopy. In both Li₂Ti₃O₇ and Li₂Ti₆O₁₃, the Li dynamics was in the focus of the studies, but also the Na dynamics in their parent compounds Na₂Ti₃O₇ and Na₂Ti₆O₁₃ was investigated. For Na₂Ti₃O₇, ²³Na NMR spectroscopy gave insights into structural and dynamic properties. A detailed ⁶Li and ⁷Li NMR spectroscopy study on Li₂Ti₃O₇ revealed 2D Li diffusion. Macroscopic cation diffusion for both Na₂Ti₃O₇ and Li₂Ti₃O₇ was investigated using impedance spectroscopy. Furthermore not only Na₂Ti₆O₁₃ and Li₂Ti₆O₁₃ were studied, but also mixed ion conductors with different Na/Li ratios. ⁶Li, ⁷Li and ²³Na NMR spectroscopy and methods as SLR and SAE were used to explore structure and dynamics of cation diffusion in Li_xNa_2-xTi₆O₁₃ (x=0,0.33,1,2). A possible 1D cation diffusion was also in the focus of this research. Impedance spectroscopy was again used for the investigation of macroscopic cation diffusion. This method revealed a mixed cation effect in Li_xNa_2-xTi₆O₁₃.