Li₀.₆[Li₀.₂Sn₀.₈S₂] – a layered lithium superionic conductor

One of the key challenges of energy research is finding solid electrolytes with high lithium conductivities comparable to those of liquid electrolytes. In this context, developing new structural families of potential Li+ ion conductors and identifying structural descriptors for fast Li+ ion conduction to occur is key to expand the scope of viable Li+ ion conductors. Here, we report that the layered material Li0.6[Li0.2Sn0.8S2] shows a Li+ ion conductivity comparable to the currently best lithium superionic conductors (LISICONs). Li0.6[Li0.2Sn0.8S2] is composed of layers comprising edge-sharing Li/SnS6 octahedra, interleaved with both tetrahedrally and octahedrally coordinated Li+ ions. Pulsed field gradient (PFG) NMR studies on powder samples show intragrain (bulk) diffusion coefficients DNMR on the order of 10−11 m2 s−1 at room temperature, which corresponds to a conductivity σNMR of 9.3 × 10−3 S cm−1 assuming the Nernst–Einstein equation, thus putting Li0.6[Li0.2Sn0.8S2] en par with the best Li solid electrolytes reported to date. This is in agreement with impedance spectroscopy on powder pellets, showing a conductivity of 1.5 × 10−2 S cm−1. Direct current galvanostatic polarization/depolarization measurements on such samples show negligible electronic contributions (less than 10−9 S cm−1) but indicate significant contact resistance (d.c. conductivity in a reversible cell is 1.2 × 10−4 S cm−1 at 298 K). Our results suggest that the partial occupation of interlayer Li+ positions in this layered material is beneficial for its transport properties, which together with tetrahedrally coordinated Li sites provides facile Li+ ion diffusion pathways in the intergallery space between the covalent Sn(Li)S2 layers. This work therefore points to a generic design principle for new layered Li+ ion conductors based on the controlled depletion of Li+ ions in the interlayer space

19F magnetic resonance imaging using vesicles of sucrose octaoleate-F104

A spin-echo technique is employed to produce high quality in vitro 19F magnetic resonance images using vesicles of a highly fluorinated sucrose octaester. The results hold promise for in vivo imaging of the gastrointestinal tract

Calcium-43 chemical shift and electric field gradient tensor interplay: A sensitive probe of structure, polymorphism, and hydration

Calcium is the 5th most abundant element on earth, and is found in numerous biological tissues, proteins, materials, and increasingly in catalysts. However, due to a number of unfavourable nuclear properties, such as a low magnetogyric ratio, very low natural abundance, and its nuclear electric quadrupole moment, development of solid-state 43Ca NMR has been constrained relative to similar nuclides. In this study, 12 commonly-available calcium compounds are analyzed via43Ca solid-state NMR and the information which may be obtained by the measurement of both the 43Ca electric field gradient (EFG) and chemical shift tensors (the latter of which are extremely rare with only a handful of literature examples) is discussed. Combined with density functional theory (DFT) computations, this 'tensor interplay' is, for the first time for 43Ca, illustrated to be diagnostic in distinguishing polymorphs (e.g., calcium formate), and the degree of hydration (e.g., CaCl2\ub72H2O and calcium tartrate tetrahydrate). For Ca(OH)2, we outline the first example of 1H to 43Ca cross-polarization on a sample at natural abundance in 43Ca. Using prior knowledge of the relationship between the isotropic calcium chemical shift and the calcium quadrupolar coupling constant (CQ) with coordination number, we postulate the coordination number in a sample of calcium levulinate dihydrate, which does not have a known crystal structure. Natural samples of CaCO3 (aragonite polymorph) are used to show that the synthetic structure is present in nature. Gauge-including projector augmented-wave (GIPAW) DFT computations using accepted crystal structures for many of these systems generally result in calculated NMR tensor parameters which are in very good agreement with the experimental observations. This combination of 43Ca NMR measurements with GIPAW DFT ultimately allows us to establish clear correlations between various solid-state 43Ca NMR observables and selected structural parameters, such as unit cell dimensions and average Ca-O bond distances. \ua9 2014 The Owner Societies.Peer reviewed: YesNRC publication: Ye

Natural abundance high field 43Ca NMR solid state NMR in cement science

This work is a systematic attempt to determine the possibilities and the limitations of the 43Ca highfield solid state NMR in the study of cement-based materials. The low natural abundance (0.135%)and small gyromagnetic ratio of 43Ca present a serious challenge even in a high magnetic field. TheNMR spectra of a number of cement compounds of known structure and composition areexamined. The spectra of several phases important in cement science, e.g., anhydrous betadi-calcium silicate (b-C2S) and tri-calcium (C3S) silicate were obtained for the first time and therelation of spectroscopic and structural parameters is discussed. The method was also applied to thehydrated C3S and synthetic calcium silicate hydrates (C?S?H) of different composition in order tounderstand the state of calcium and transformations in the structure during hydrolysis. The spectraof hydrated C3S reveals a calcium environment similar to that of the C?S?H samples and 11 A \ub0Tobermorite. These observations support the validity of using layered crystalline C?S?H systems asstructural models for the C?S?H that forms in the hydration of Portland cement.Ces travaux constituent une tentative syst\ue9matique de d\ue9termination des possibilit\ue9s et des limites inh\ue9rentes \ue0 la r\ue9sonance magn\ue9tique nucl\ue9aire (RMN) de haute r\ue9solution et \ue0 \ue9tat solide du 43Ca dans l?\ue9tude des mat\ue9riaux cimentaires. La teneur isotopique naturelle faible (0,135 %) de m\ueame que le faible rapport gyromagn\ue9tique du 43Ca pr\ue9sentent un d\ue9fi de taille, m\ueame lorsque le champ magn\ue9tique est \ue9lev\ue9. Les spectres de RMN d?un certain nombre de compos\ue9s cimentaires d?une structure et d?une composition connues sont ici examin\ue9s. Les spectres de plusieurs phases importantes dans la science des ciments, p. ex., silicate bicalcique anhydre de forme b\ueata (b-C2S) et silicate tricalcique (C3S), ont \ue9t\ue9 obtenus pour la premi\ue8re fois, et l?on examine la relation des param\ue8tres spectroscopiques et structuraux. La m\ue9thode fut \ue9galement appliqu\ue9e aux C3S hydrat\ue9s et aux hydrates de silicate de calcium (C?S?H) de composition diff\ue9rente, aux fins de la compr\ue9hension de l?\ue9tat du calcium et des transformations dans la structure en cours d?hydrolyse. Les spectres des C3S hydrat\ue9s r\ue9v\ue8lent un environnement calcique semblable \ue0 celui des \ue9chantillons de C?S?H et de tobermorite 11A. Ces observations viennent appuyer la validit\ue9 de l?utilisation de syst\ue8mes cristallins en couches de C?S?H comme mod\ue8les structuraux pour le C?S?H qui se forme dans l?hydratation du ciment Portland.Peer reviewed: YesNRC publication: Ye

131Xe, a new NMR probe of void space in solids

NRC publication: Ye

Methane and carbon dioxide hydrate formation in water droplets : spatially resolved measurements from magnetic resonance microimaging

We have used 1H magnetic resonance microimaging to probe both methane and carbon dioxide hydrate formation processes inside dispersed water droplets. When bulk techniques such as gas uptake measurements are used for determining the kinetics of hydrate formation, these show a gradual conversion to hydrate, suggesting a relatively homogeneous process that might be modeled using a set of intrinsic kinetic parameters. The spatially resolved microimaging measurements show that in fact the conversion to hydrate is quite inhomogeneous, some drops converting quickly, others requiring hours or days. This indicates that the observation of gradual conversion in bulk samples only arises as a result of averaging over many local environments. Quantitative measurements of kinetic processes in subvolumes of a larger sample suggests that the smaller the volume observed, the more inhomogeneous the process appears to be. When hydrate-coated water droplets in 3,5,5-trimethylpentane are converted to hydrate, there is evidence that nucleation can take place well away from the hydrate coating, with the hydrate sometimes growing in discrete steps before drops are completely converted. The results obtained indicate that in the quiescent systems studied here the definition of intrinsic kinetic parameters will be difficult, if possible at all, because of a stochastic component that competes with more gradual conversion processes.Peer reviewed: YesNRC publication: Ye

Titanium carbide, nitride and carbonitrides: a 13C, 14N, 15N and 47,49Ti solid-state nuclear magnetic resonance study

The first 47,49Ti, 13C, 14N and 15N solid-state nuclear magnetic resonance (NMR) spectra of titanium carbide, nitride and a series of cubic carbonitrides have been obtained under both static and magic-angle spinning (MAS) conditions. The 15N samples were isotopically enriched by gas-solid exchange at 1000 \ub0 C in a closed system. The Ti spectra of the carbide and nitride are sharp, reflecting the well defined cubic symmetry of these compounds, but become considerably broadened in the carbonitride series, with the spectra being approximately the sum of TiC and TiN together with some small electric field gradient (EFG) effects. The resonance positions and widths of all the NMR spectra change as carbon is progressively replaced by nitrogen. A relationship is observed between the 13C chemical shift and the nitrogen content of the carbonitrides, suggesting a possible NMR method for estimating the composition of these compounds. Although electron paramagnetic resonance (EPR) spectra of all these compounds show typically metallic behaviour, the NMR spectra show few effects attributable to conduction electrons, probably due to the lack of s-orbital contributions to the conduction band.Peer reviewed: YesNRC publication: Ye