Li6andLi7NMR line-shape and stimulated-echo studies of lithium ionic hopping in

Abstract

6 Li and 7 Li NMRs are used to investigate the lithium ion dynamics in LiPO 3 glass. In particular, 6 Li NMR stimulated-echo experiments are used to provide straightforward access to two-time correlation functions characterizing the lithium ionic hopping motion in the millisecond regime in a glassy ion conductor. Temperature-dependent measurements serve to separate the spin diffusion contribution and the dynamic contribution to the stimulated-echo decays. The 6 Li NMR correlation functions of LiPO 3 glass describing the lithium ionic motion show pronounced nonexponential decays, which can be well described by a stretched exponential function with a temperature-independent small stretching parameter ␤ = 0.27, indicating the complex nature of the lithium dynamics. The temperature dependence of the mean correlation times ͗͘ resulting from these stimulated-echo experiments is described by an activation energy E a = 0.66 eV. The values of ͗͘ are in good agreement with time constants from previous electrical and mechanical relaxation studies. At appropriate temperatures, the 6 Li and 7 Li NMR spectra are superpositions of a broad and a narrow spectral component, which result from slow and fast lithium ions, respectively, on the NMR time scale. A detailed analysis of the temperature dependence of these line shapes provides information about the distribution of correlation times.

Atomic-scale measurement of ultraslow Li motions in glassyLiAlSi2O6by two-timeL6Wilkening1, Kuhn2, Heitjans3 2008Phys. Rev. B594500View full textAdd to dashboardCite

“…The mean value ␥ is 0.29͑1͒ between 300 and 390 K. The small stretching factor indicates the presence of a distribution of jump rates and, thus, reflects the complex Li diffusion process in glassy LiAlSi 2 O 6 . Correlation functions with nearly the same stretching factor were also observed for LiPO 3 glass by Faske et al, 47 quite recently, and ascribed to dynamical heterogeneities rather than to intrinsically nonexponential correlation functions due to, e.g., forward-backward jump processes being certainly of relevance for the fast ions. The logarithm of the corresponding decay rates SAE −1 of the correlation functions measured at t p = 100 s are plotted vs 1 / T in Fig.…”

“…24, and corroborated for 6 Li on a Li 3 N single crystal ͑Ref. 26͒ as well as by a subsequent study by Faske et al on LiPO 3 glass, 47 the measurement of 6 Li stimulated echoes provides access to long-range diffusion parameters probed directly, i.e., without involving a model, by means of a microscopic technique.…”

“…To our knowledge only a few more 7 Li SAE NMR experiments have been applied so far on glassy materials. The first and so far the only 6 Li SAE NMR study on a glass viz LiPO 3 was just published by Faske et al 47 In contrast to that work, in the present study we have used an isotopically nonenriched sample with the natural 6 Li abundance of about 7.5%. Thus, spin-diffusion effects caused by dipole-dipole interactions are almost eliminated.…”

New Lithium Chalcogenidotetrelates, LiChT: Synthesis and Characterization of the Li+-Conducting Tetralithium ortho-Sulfidostannate Li4SnS4

“…Since the motional narrowing effects appear, with temperature, at first for that subset of lithium ions having the highest mobility, the Waugh−Fedin method tends to underestimate the value of the activation energy when a distribution is present. 33 This fact explains why in disordered materials such E A values from static NMR data are often found to be lower than those determined by dc−ionic conductivity measurements. 34 As indicated in the following, this is also the case for the present material.…”

First and Second Universalities: Expeditions Towards and Beyond

“…This includes friends and colleagues both inside and outside SFB 458, as well as KF's past coworkers. To name just a few, in alphabetical order, we would especially like to thank A. Bunde Besides thanking our friends at SFB 458 for an atmosphere of intense engagement and healthy exchange of views, we also would like to cite a few relevant results of theirs [110][111][112][113][114][115][116][117][118][119][120][121][122][123][124][125][126] which have added new insights while addressing issues complementary to those treated in this overview.…”