Silver ion dynamics in the Ag₅Te₂Cl-polymorphs revealed by solid state NMR lineshape and two- and three-time correlation spectroscopies

Abstract

The relation between structure and ion dynamics in the three polymorphs of Ag(5)Te(2)Cl has been investigated using (109)Ag, (125)Te, and (35)Cl NMR spectroscopies. Specifically, the influence of the structural phase transitions observed near 240 K (P2(1)/c<-->P2(1)/n) and near 332 K (P2(1)/n<-->I4/mcm) upon silver ion mobilities has been studied by temperature dependent (109)Ag NMR lineshapes and spin-lattice relaxation times. While the superionic high temperature phase alpha-Ag(5)Te(2)Cl is characterized by a molten cationic sublattice, fast ion dynamics in the medium-temperature phase beta-Ag(5)Te(2)Cl occurs in spatially restricted regions comprising all the crystallographically distinct silver sites. Temperature dependent magic-angle-spinning linewidths yield an activation energy of 0.38 eV, consistent with 0.44 eV measured from dc electric conductivities. For the low-temperature gamma-modification, results of two- and three-time (109)Ag correlation spectroscopies provide a detailed insight into the nature of the silver ionic hopping motion. Temperature dependent jump rates measured by two-time correlation functions yield an activation energy E(a)= 0.48 eV. (109)Ag NMR three-time correlation functions indicate that the non-exponential relaxation behavior of the silver ions can be attributed to a broad distribution of jump rates rather than correlated forward-backward jumps. Nevertheless, all the silver ions are mobile down to temperatures of about 185 K.

Li jump process inh−Li0.7TiS2studied by two-timeWilkening1, Heitjans2 2008Phys. Rev. B9881581View full textAdd to dashboardCite

“…This similarity was also found for the interlayer Li diffusion process in single-crystalline Li 3 N, 32 as well as for the cation transport in Ag ion conductors where the dynamic properties were probed by multiple-time 109 Ag stimulated echo NMR. 69,75 The activation energy for singlecrystalline h-Li Ϸ0.7 TiS 2 obtained from electrochemical methods is about 0.4 eV. 94 This value is remarkably similar to those probed by 7 Li SAE NMR here.…”

“…The method was then used by Böhmer and co-workers 58,59 to investigate ultraslow Li motions in crystalline Li 3 68 It is worth mentioning in this context that 109 Ag stimulated echo NMR two-and four-time correlation functions were recorded recently to investigate silver dynamics in glasses of the compositions ͑AgI͒ x -͑AgPO 3 ͒ ͑1−x͒ , [69][70][71][72] 73 as well as in several other Ag compounds. 74,75 In contrast to spin-1 and spin-3 / 2 nuclei, in the case of the nonquadrupolar 109 Ag nucleus with I =1/ 2 chemical shift interactions are used to differentiate between the ions.…”

New prospects in studying Li diffusion—two-time stimulated echo NMR of spin-3/2 nuclei

“…In addition to the direct measurement of ultra-slow Li jump rates, SAE-NMR in general serves as a tool for the investigation of geometric properties of diffusion pathways [15,36]. The first decay step of the two-time correlation function of Fig.…”

“…Deuteron SAE-NMR evolved into a powerful technique to precisely study the dynamics as well as geometric aspects of diffusion processes. Quite recently, stimulated echo NMR was also used to study successfully Ag dynamics, using the spin-1/2 nucleus 109 Ag, in crystalline and glassy materials [14][15][16].…”

Silver(I)-(poly)chalcogenide Halides – Ion and Electron High Potentials

“…A detailed analysis of the joint probability density functions (jpdf) between the different silver positions led to a detailed insight in the preferred diffusion pathways in these compounds. Two-and three-time correlation spectroscopies were performed for Ag 5 Te 2 Cl [72] in order to understand the silver dynamics of this substance class in more detail.…”