NMR Studies of Lithium Diffusion in Li3(NH2)2I over Wide Range of Li+ Jump Rates

We have studied the Li diffusion in the complex hydride Li3(NH2)2I which appears to exhibit fast Li ion conduction. To get a detailed insight into the Li motion, we have applied 7Li nuclear magnetic resonance spectroscopy methods, such as spin-lattice relaxation in the laboratory and rotating frames of reference, as well as spin-alignment echo. This combined approach allows us to probe Li jump rates over the wide dynamic range (~102–109 s−1). The spin-lattice relaxation data in the range 210–410 K can be interpreted in terms of a thermally-activated Li jump process with a certain distribution of activation energies. However, the low-temperature spin-alignment echo decays at T≤200 K suggest the presence of another Li jump process with the very low effective activation energy. © 2017 Walter de Gruyter GmbH, Berlin/Boston 2017

Li dynamics in amorphous LiNbO 3 as probed by solid state NMR on different length scales

Long-range Li diffusion parameters of amorphous LiNbO3 are probed by 7Li two-time spin-alignment echo NMR spectroscopy which is sensitive to slow Li dynamics. The jump rates which were extracted from the spin-alignment echo decay curves exhibit Arrhenius behaviour between 293 K and 413 K. The activation energy (0.41(1)eV) is in good agreement with that of the high-temperature flank of the 7Li NMR spinlattice relaxation rate peak. The latter was predicted to be about 0.4 eV when taking into account the frequency dependence of the corresponding spin-lattice relaxation rates on the low-T flank (see Wilkening et al., Phys. Chem. Chem. Phys. 4 (2002) 3246). Previous measurements of the spin-lattice relaxation rate had to be restricted to temperatures below 450 K in order to avoid crystallization of the material. Thus, only the low-temperature flank of the diffusion induced spin-lattice relaxation rate peak had been accessible yielding information about short-range Li diffusion

Slow Atomic Motion in Zr-Ti-Cu-Ni-Be Metallic Glasses Studied by NMR

Nuclear magnetic resonance is used for the first time to detect slow atomic motion in metallic glasses, specifically, Be motion in Zr-Ti-Cu-Ni-Be bulk metallic glasses. The observations are not consistent with the vacancy-assisted and interstitial diffusion mechanisms and favor the spread-out free volume fluctuation mechanism for Be diffusion. Comparison with the results of Be diffusion measured by elastic backscattering the NMR results also indicates that the energy barriers for short- and long-range Be motion are the same

Experimental evidence for the relaxation coupling of all longitudinal 7Li magnetization orders in the superionic conductor Li10GeP2S12

This contribution addresses the experimental proof of the relaxation coupling of the 7Li (I = 3/2) longitudinal magnetization orders in the solid-state electrolyte Li10GeP2S12 (LGPS). This effect was theoretically described by Korb and Petit in 1988 but has not yet been shown experimentally. In a 2D-T1/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 Multi-quantum-filter experiments and by simulations of the 2D-T1/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 especially in fast Li-ion conductors as a separation tool for environments with different mobility processes

Li jump process in h- Li0.7 Ti S2 studied by two-time Li7 spin-alignment echo NMR and comparison with results on two-dimensional diffusion from nuclear magnetic relaxation

7Li spin-alignment NMR is used to trace ultraslow diffusion of Li+ in the layered Li conductor LixTiS2 (x=0.7). Two-time correlation functions were recorded for fixed evolution times as a function of mixing time at temperatures within the 7Li rigid-lattice regime. The corresponding decay rates were identified as Li jump rates τ−1 ranging from 10−1to103s−1 between temperatures T=148 K and 213K. The jump rates obtained directly from spin-alignment echo NMR and those from diffusion induced maxima of spin-lattice relaxation peaks, monitored in the laboratory as well as in the rotating frame, are consistent with each other and follow an Arrhenius law with an activation energy of 0.41(1)eV and a preexponential factor of 6.3(1)×1012s−1. Altogether, a solitary Li diffusion process was found between 148 and 510K. Li diffusion was investigated in a dynamic range of about 10 orders of magnitude, i.e., 0.1⩽τ−1⩽7.8×108s−1. Additionally, the analysis of final-state echo amplitudes of the two-time correlation functions revealed information about the Li diffusion pathway in Li0.7TiS2. Obviously, a two-site jump process is present, i.e., besides the regularly occupied octahedral sites also the vacant tetrahedral ones within the van der Waals gap are involved in the overall two-dimensional diffusion process. © 2008 The American Physical Society

Atomic-scale measurement of ultraslow Li motions in glassy LiAlSi2 O6 by two-time L6 i spin-alignment echo NMR correlation spectroscopy

6Li spin-alignment echo (SAE) nuclear-magnetic-resonance (NMR) spectroscopy is used to monitor single-particle two-time correlation functions in LiAlSi2O6 glass. The method, here applied in the temperature range from 300 to 400 K, is sensitive to ultraslow Li hopping processes with rates (1/τSAE) down to 10 jumps/s. The use of a sample with natural 6Li abundance allowed the measurement of pure NMR spin-alignment echoes which are damped with increasing mixing time exclusively by slow Li jumps, i.e., free of influences arising from, e.g., interfering spin-diffusion effects. The considerably stretched correlation functions reveal the presence of a broad distribution of jump rates. The results are comprehensively compared with those recently obtained from both 7Li SAE and 7Li spin-lattice relaxation NMR as well as from dc conductivity measurements. Interestingly, the activation energy of the latter, which are sensitive to long-range Li transport parameters, is in good agreement with that microscopically probed by 6Li SAE NMR, here. © 2008 The American Physical Society

NMR and Impedance Spectroscopy Studies on Lithium Ion Diffusion in Microcrystalline γ-LiAlO2

In this work nuclear magnetic resonance (NMR) and impedance spectroscopy (IS) studies on Li ion dynamics in microcrystalline γ-LiAlO2 are presented. The sample was prepared by solid state synthesis between Li2CO3 and Al2O3 in air, followed by a quenching procedure. The presence of phase-pure γ-LiAlO2 was confirmed by X-ray powder diffraction including Rietveld refinement. Further structural characterization was done with 6Li, 7Li and 27Al NMR. Several NMR techniques such as spin-lattice relaxation measurements, motional narrowing experiments, as well as spin-alignment echo were employed for the investigation of Li ion diffusion. The measurements were carried out at high temperatures (up to 970 K) in order to access the regime of Li ion motion being very slow. The dc conductivities measured by IS in the temperature range from 680 K to 870 K were converted to diffusion coefficients being compatible with those obtained by NMR. © 2015 Walter de Gruyter

Local Ion Dynamics in Polycrystalline β-LiGaO2: A Solid-State NMR Study

Solid-state nuclear magnetic resonance spectroscopy is an efficient technique to characterize dynamics and structure of materials. It has been widely used to elucidate ion dynamics in lithium ion conductors. Fast moving lithium ions are needed in energy storage devices, whereas slow ion motion is exploited in some materials used, for example, as blankets in fusion reactors. β-lithium gallium oxide (LiGaO2) is a slow Li+ ionic conductor similar to γ-lithium aluminum oxide (LiAlO2). In an ion conductor, in addition to the main diffusion process, localized motions (to-and-fro jumps) may be present. In the present work, with the help of solid-state NMR experiments, we report on the localized movements of Li+ ionic species in β-LiGaO2 in the temperature range between 300 K and 450 K. In this work, we have mainly extracted the peculiarities of ion dynamics from 7Li spin-alignment echo NMR measurements and the observation of the motional narrowing of the central transition signal of 7Li. © 2017 Walter de Gruyter GmbH, Berlin/Boston 2017

Studying Li dynamics in a gas-phase synthesized amorphous oxide by NMR and impedance spectroscopy

Li diffusion parameters of a structurally disordered Li-Al-Si-oxide prepared by gas-phase synthesis were complementarily investigated by both time-domain NMR techniques and impedance spectroscopy. The first include 7Li NMR spin-lattice relaxation (SLR) measurements in the laboratory as well as in the rotating frame of reference. An analysis of variable-temperature NMR line widths point to an activation energy E a of approximately 0.6 eV. The value is confirmed by rotating-frame SLR NMR data recorded at approximately 11 kHz. Above room temperature the low-temperature flank of a diffusion-induced rate peak shows up which can be approximated by an Arrhenius law yielding E a = 0.56(1) eV. This is in very good agreement with the result obtained from 7Li spin-alignment echo (SAE) NMR being sensitive to even slower Li dynamics. For comparison, dc-conductivity measurements, probing long-range motions, yield E a = 0.8 eV. Interestingly, lowtemperature SAE NMR decay rates point to localized Li motions being characterized with a very small activation energy of only 0.09 eV. © by Oldenbourg Wissenschaftsverlag, München