Investigation of structure and dynamics in solid electrolyte materials and glass forming liquids using high resolution and high temperature nuclear magnetic resonance spectroscopy

Multinuclear solid state NMR spectroscopy has been applied to study the atomic-scale structure and dynamics in Solid Electrolyte (SE) materials used in Solid Oxide Fuel Cells (SOFCs). The effects of crystallite size on cation coordination environments and oxygen vacancy ordering have been investigated in micro- and nano-crystalline Y- and Sc- doped ZrO2 and CeO 2 using high-resolution 89Y and 45Sc magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Preferences for oxygen vacancies to be associated with any particular cation is significantly reduced in nano-crystalline samples which exhibit a more randomized distribution of oxygen vacancies and a higher degree of short-range structural disorder compared to their micro-crystalline counterparts.;High temperature NMR has been applied to a model solid electrolyte to understand better the role of crystallite size on ionic conductivity. An atomistic study of oxygen-vacancy hopping dynamics in microcrystalline (200nm), intermediate-sized (50nm) and nano-crystalline (5nm) Sc-doped CeO2 using 45 Sc magic-angle-spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy has also been carried out. In the case of micro-crystalline SDC, the temperature dependence of the oxygen-vacancy hopping frequency, as obtained from NMR results, is in good agreement with that obtained from impedance spectroscopy. On the other hand, these oxygen vacancies are found to be largely immobile in nano-crystalline SDC even at temperatures as high as 600°C. These results indicate that the nano-structuring of this SE material will unlikely benefit its anionic conductivity.;19F MAS NMR spectroscopy has been applied to study the structure and F--ion dynamics in nano-crystalline CaF 2. The 19F MAS NMR spectra of nano-crystalline CaF 2 (diameter ∼ 25 nm) show the presence of ∼ 0.55% of the F - ions in interstitial sites that are found to be highly mobile at elevated temperatures and undergo rapid site exchange with regular fluorine sites in the lattice via hopping. It is shown that an increased concentration of these defects formed in nano-crystalline CaF2 may result in an enhancement in ionic conductivity by nearly 3 orders of magnitude compared to that of bulk CaF2.;Finally, the idea of dynamical NMR line shape analysis has been extended to study the molecular structure and dynamics of supercooled glycerol in bulk and under nanoconfinement using 13C NMR. It is found that alpha-relaxation in supercooled glycerol is controlled primarily by isotropic reorientational jumps of the constituent molecules. Under nanoconfinement, the temperature dependence of the timescale of this tumbling motion changes from non-Arrhenius to Arrhenius type. The observed changes in the timescale of the rotational dynamics of the constituent molecules and in its temperature dependence are hypothesized to result from confinement induced change in the structure and density of glycerol.;31P NMR has been applied to study the role of glass forming sugars in the preservation of dipalmitoylphosphatidylcholine (DPPC) lipid bilayers. 31P wideline NMR spectra of freeze-dried pure DPPC, DPPC/trehalose, DPPC/glucose and DPPC/hydroxyethyl starch (HES) mixtures, collected in the temperature range 25°C -- 80°C, have been simulated to obtain quantitative information about rotational dynamics and orientation of the lipid head groups in these media. Trehalose reduces the lipid head group motions most effectively in the temperature range of T ≤ 50°C relevant for biopreservation. Additionally, and possibly more importantly, trehalose is found to strongly restrict any change in the orientation of the diffusion axis of the PO4 head groups during the phase transformation. This unique ability of trehalose to maintain the dynamical and orientational rigidity of lipid head groups is likely to be responsible for its superior ability in biopreservation.