LiGePS (LGPS) is the fastest known Li-ion conductor to date due to the formation of one-dimensional channels with a very high Li mobility. A knowledge-based optimization of such materials for use, for example, as solid electrolyte in all-solid-state batteries requires, however, a more comprehensive understanding of Li ion conduction that considers mobility in all three dimensions, mobility between crystallites and different phases, as well as their distributions within the material. The spin alignment echo (SAE) nuclear magnetic resonance (NMR) technique is suitable to directly probe slow Li ion hops with correlation times down to about 10 s, but distinction between hopping time constants and relaxation processes may be ambiguous. This contribution presents the correlation of the Li spin lattice relaxation (SLR) time constants (T) with the SAE decay time constant τ to distinguish between hopping time constants and signal decay limited by relaxation in the τ distribution. A pulse sequence was employed with two independently varied mixing times. The obtained multidimensional time domain data was processed with an algorithm for discrete Laplace inversion that does not use a non-negativity constraint to deliver 2D SLR-SAE correlation maps. Using the full echo transient, it was also possible to estimate the NMR spectrum of the Li ions responsible for each point in the correlation map. The signal components were assigned to different environments in the LGPS structure.
Two calcined products of Li 6.4 Fe 0.2 La 3 Zr 2 O 12 can be synthesized via the solid state method and the sol gel method. Inhomogeneities of the iron distribution in the powder for the solid state method lead to a combination of cubic and tetragonal structure. By using the sol gel method the homogeneity can significantly been increased resulting in the desired pure phase cubic structured powders in I43d. By in situ dilatometer measurements the densification process can be comprehended for the first time for garnet type materials. The density can be significantly increased by the usage of the sol gel synthesis compared to the solid state synthesis with short sintering times of 2 h delivering pure phase pellets for both synthesis methods. Electrical impedance measurements revealed clearly divided semicircles for the bulk and the grain boundary contribution for the solid state synthesis, while the sol gel synthesis showed only one semicircle from the bulk contribution due to a large crystallite size. The total ionic conductivity for the pellet synthesized via the sol gel method is 1.82 mS/cm at 25 • C which is the fastest found so far for garnet type or garnet related materials.
This contribution addresses the experimental proof of the relaxation coupling of the 7 Li (I=3/2) longitudinal magnetization orders in the solid-state electrolyte Li 10 GeP 2 S 12 (LGPS). This effect was theoretically described by Korb and Petit in 1988 but has not yet been shown experimentally. In a 2D-T 1 /spin-alignment echo (SAE) experiment, the inverse Laplace transformation of the spectral component over two time dimensions revealed the asymmetric course of the spin-lattice relaxation following from the coupling of all longitudinal orders. These observations were supported by Multiquantum-filter experiments and by simulations of the 2D-T 1 /SAE experiment with a lithium spin system. Since the asymmetric relaxation effects are directly dependent on the velocities and degrees of freedom of ion motion they could be used esspecially in fast Li-ion conductors as a seperation tool for environments with different mobility processes.
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