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A unified model of ionic motion in glasses is presented which relates consistently the different quantities observed in nuclear-spin relaxation and electrical-conductivity relaxation due to thermally activated ionic diffusion. Corresponding experimental data obtained in a low-ionic-conductivity fluorozirconate glass are shown to be in reasonable agreement with the present approach. Limitations of the model are pointed out and are discussed in view of observed deviations between the different experimental results.

The reorientational motion of the tetrahydrofuran guest molecule in the clathrate hydrate C4H8O · 17D2O was studied by proton NMR spin‐lattice relaxation measurements in the temperature range 4 — 278 K. The results are interpreted by a Davidson‐Cole distribution of correlation times with a distribution parameter ß = 0.12. The maximum or cutoff time τ0 in this distribution obeys an activation law with prefactor 3.75 · 10−13 s and activation energy 4140 J mol−1. At temperatures below 20 K the motion of the guest molecules can be described by a coupled ensemble of quantummechanical hindered rotators where the reorientation rate is again described by a Davidson‐Cole distribution.

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We have determined NMR linewidths and nuclear spin relaxation rates for F, Li, and Na nuclei, and electrical conductivity in ZrF 4-based fluoride glasses as a function of temperature. The results indicate that both Li and F are mobile in the glass containing 20 mole% LiF, whereas only F is mobile in glasses containing NaF (up to 30 mole%) or no alkali ions. Finally we compare and discuss the activation energies for the various parameters. RESUME Des mesures de conductivité électrique et de RMN de F, Li et Na ont e'te' re'alise'es sur des verres fluorures à base de ZrF 4 : les variations des largeurs de raies de résonance et des temps de relaxation ont été e'tudie'es en fonction de la température. Les résultats démontrent que les ions Li et F sont mobiles dans le verre contenant 20% de LiF(en fraction molaire). Dans le cas des verres contenant du NaF (jusqu'à 30% en mole) ou ne contenant pas de cation alcalin, seul l'ion F est mobile. Les e'nergies d'activation déduites des divers paramétres sont comparées et analysées.

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We show that NMR stimulated-echo experiments provide detailed information about the jump dynamics of each of the ionic species in mixed mobile ion glasses. The potential of this technique is exploited to measure two-time correlation functions of the lithium and silver ionic hopping motions in Li x Ag 1−x PO 3 glasses. Comparison of stimulated-echo decays from 6 Li or 7 Li NMR with that from 109 Ag NMR shows that the residence times at the ionic sites are significantly longer for the respective minority component than for the majority component at both ends of the composition range, while lithium and silver ions exhibit similar jump rates for x = 0.5. Substitution of silver by lithium results in a strong and continuous slowdown of the silver ionic jumps, whereas the lithium ionic jumps show a weaker dependence on the glass composition. In the vicinity of the conductivity minimum, the activation energies obtained from the stimulated-echo studies for both lithium and silver ionic jumps are significantly smaller than that obtained from the dc conductivity. This suggests that mixing of cation species promotes differences between short-range and long-range ionic motions. For all studied glass compositions and for both lithium and silver, we can rule out the existence of a significant fraction of truly immobile cations. However, broad distributions of jump rates lead to strongly nonexponential correlation functions of the ionic hopping motion. Interestingly, the correlation functions become more and more exponential when the observed cation species is successively replaced by the unobserved cation species. The present results suggest that dynamical heterogeneities and correlations of ionic motions, which involve like and unlike ions and length scales of several interatomic distances, are important aspects of ion dynamics in mixed mobile ion glasses.

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