Mixed-cation LixAg1−xPO

Abstract

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.

NMR Multi-Time Correlation Functions of Ion Dynamics in Solids

“…More detailed insights into the mixed cation effect of Li x Ag 1−x PO 3 glasses are available when analyzing the dependence of the 6 Li and 109 Ag NMR 2T-CF on temperature and composition. These results will be published elsewhere [41]. Below, we will use 6 Li and 109 Ag NMR 3T-CF to investigate the origin of the nonexponential ionic relaxation in Li 0.5 Ag 0.5 PO 3 glass.…”

From Micro to Macro: Access to Long‐Range Li+ Diffusion Parameters in Solids via Microscopic 6, 7Li Spin‐Alignment Echo NMR Spectroscopy

“…Inspired by the pioneering theoretical and experimental studies of Wu et al and Bçhmer et al, spin-alignment NMR spectroscopy was then used to characterize lithium diffusion in a number of materials in different structural forms. For example, Li dynamics have been studied in: 1) single crystals of b-eucryptite (LiAlSiO 4 ) [30,39] and Li 3 N; [54] 2) polycrystalline materials such as the hexagonal [38,40] and cubic form of Li x TiS 2 , [55] Li 4 Ti 5 O 12 , [56] Li 4 SiO 4 , [49] Li 7 BiO 6 , [41] the aluminosilicate LiAlSi 2 O 6 , [45] and the garnet Li 5 La 3 Nb 2 O 12 ; [57] 3) nanostructured materials such as Li x TiO 2 nanowires; [58,59] and 4) highly disordered ceramics and glasses such as LiPO 3 [60] and the cation-mixed glass Li x Ag 1Àx PO 3 (0 x 1) [43] as well as b-spodumene LiAlSi 2 O 6 , [45,61] amorphous LiNbO 3 [62] and the glass ceramic Zerodur M. [63] Recently, longrange Li transport parameters have also been probed in Li 2 TiO 3 , which is, in its crystalline form, an extremely poor ionic conductor. [64] It is worth mentioning that Vogel et al used 109 Ag stimulated-echo NMR spectroscopy to record two-and four-time correlation functions.…”

“…In this way they studied silver dynamics in several crystalline [65,66] and glassy materials [67][68][69][70][71] including the aforementioned Li x Ag 1Àx PO 3 . [43] By using 109 Ag NMR spectroscopy they took advantage of site-specific chemical shift interactions to differentiate between magnetically nonequivalent silver ions. Vogel and co-workers clearly showed that the diffusion parameters probed by 109 Ag NMR stimulated echoes agree with those deduced from dc-conductivity measurements [65] that are sensitive to long-range transport of silver ions.…”

Extremely slow Li ion dynamics in monoclinic Li2TiO3—probing macroscopic jump diffusion via7Li NMR stimulated echoes

“…This (single-spin) correlation function, which is given by the NMR spin-alignment echo height S 2 vs. t m , contains the information about the probability of finding a spin, which was exposed to o Q at t 0 = 0, in the same state, i.e., exposed to the same quadrupole frequency, at a later time t 0 = t m . [16][17][18][19]23,25,52,56,57 In many cases S 2 , which is here given by…”