Local and global dynamics of the viscous ion conductors 2Ca(NO3)2-3KNO3 and 2Ca(NO3)2-3RbNO3 probed by 87Rb nuclear magnetic resonance and shear rheology

Abstract

The microscopic and macroscopic dynamics of calcium alkali nitrate melts are studied in their supercooled regime by means of shear rheology and nuclear magnetic resonance (NMR). The structural relaxation is probed using shear rheology to access the viscoelastic flow as well as using physical aging experiments. By exploiting the strongly quadrupole-perturbed 87Rb nucleus, the local dynamics is probed on the milliseconds to nanoseconds range using various NMR methods involving central-transition stimulated-echo techniques, line shape analyses, spin relaxations, and second-order dynamic shift effects. The time scales monitored via the local Rb probe are in harmony with the electrical conductivity relaxation times. The low-temperature NMR line shapes agree excellently with those predicted by the Czjzek model. The temperature dependent second-order dynamic frequency shift is described using the imaginary part of the spectral density. It is demonstrated how the latter quantity can be generalized to include effects of correlation time distributions.

Translational and reorientational dynamics in deep eutectic solvents

“…Overall, the application of the RBM seems to be straightforward for ionic conductors without dipolar degrees of freedom such as the often-investigated ionic melt [Ca(NO 3 ) 2 ] 0.4 [KNO 3 ] 0.6 (Ref. 61), but some care is necessary for materials involving dipolar reorientations.…”

“…We ascribe these to spurious contributions in J ′ (ν) due to the low-torque limitations of the rheometer. 48,49,55,61 To a lesser extent, they also affect the glyceline spectra [cf. the two highest temperatures in Fig.…”

“…As shown in Ref. 52, the 2008 version of the RBM is, however, able to describe the data of ILs without the need to take such slow contributions into account. Interestingly, in Ref.…”

“…Overall, the application of the RBM seems to be straightforward for ionic conductors without dipolar degrees of freedom like the ofteninvestigated ionic melt [Ca(NO 3 ) 2 ] 0.4 [KNO 3 ] 0.6 (Ref. 52), but some care is necessary for materials involving dipolar reorientations. Dielectric data for ionically conducting materials are often presented in terms of the complex dielectric modulus, M * = M' + i M" = 1/ * .…”

О причинах асимметричности формы контура колебательной полосы ν-=SUB=-1-=/SUB=-(A-=SUB=-1-=/SUB=-) в спектрах комбинационного рассеяния света расплава LiNO-=SUB=-3-=/SUB=-

“…Исследованию динамики молекулярного аниона NO 3 в расплавленных нитратах методами колебательной спек-троскопии посвящен ряд обзорных и оригинальных статей [10][11][12][13][14]. Хорошо известно, что контур линии, отвечающей колебанию ν 1 (A 1 ) нитрат-иона в расплавах, асимметричен [15].…”