PFG NMR Research Articles

Dynamics of Bottlebrush Polymers in Solution by Neutron Spin Echo Spectroscopy

We present dynamical and morphological studies on poly(dimethylsiloxane) (PDMS)-based bottlebrush polymers in solution. A combination of small-angle neutron scattering (SANS), pulsed field gradient nuclear magnetic resonance (PFG NMR), and neutron spin echo (NSE) spectroscopy was used to identify structural changes inherent in changing the side-chain length while keeping the backbone constant. These morphological changes are mirrored in the diffusion coefficient determined by PFG NMR, resulting in two coefficients for the elongated and one for the more spherical sample. Faster motions are tracked by NSE using the advantage of time- and length-scale resolutions with the diffusion coefficient predetermined by PFG NMR. Hereby, the sample with short side chains relaxes like wormlike micelles considering the longitudinal direction, whereas the dynamics along the radial extension shows a much stronger Q-dependence as known from any theory. The dynamical behavior within the blob region, covered with the more spherical sample, follows the predictions of Zimm as well as of Zilman and Granek (ZG).

Achieving Enhanced Mobility of Ions in Ionic Liquid-Based Gel Polymer Electrolytes By Incorporating Inorganic Nanofibers for Li-Ion Battery

Polymer electrolytes have received much attention in Li-ion battery research because of their unique properties, such as, high ionic conductivity, high mechanical strength including good electrode-electrolyte contact. A major research has been focused on improving the conductivity while retaining the mechanical stability of polymer electrolytes. In this context, ionic liquid-based gel polymer electrolytes are an excellent candidate. A detailed NMR investigation of PMMA-ILs gels electrolytes probing the structure and dynamics of ions was recently reported.[1] The presence of ILs in polymer matrix not only improves the conductivity but also enhances the self-healing capability. In another study, self-healing capability that reduces the dendrite formation at the interface has been discovered, for example, in PVDF-HFP-ILs electrolyte.[2] In this regard, this work reports the possible ways to enhance the ionic conductivity of such polymer electrolyte further by adding Al2O3 nanofibers. A series of PVDF-HFP-ILs with 1M LiTFSI in EMIMTFSI at different ratios of Al2O3nanofibers were prepared through solution cast technique. The dynamics of ions confined within polymer-Al2O3 matrix was explored through Impedence and PFG NMR spectroscopy. The amorphocity and the distribution of Al2O3 nanofibers are studied through XRD and SEM-EDX analyses. Lastly, the local structure of ions and their interaction with polymer and Al2O3 nanofibers were established through a detailed solid-state NMR analyses detecting 1H, 27Al, 13C, 19F, 7Li nuclei including 2D 13C{1H} HETCOR experiments. A reasonable enhancement in terms of ionic conductivity was observed with the addition of Al2O3 nanofibers, which improves the conducting pathways within the polymer network.[1] M. N. Garaga, N. Jayakody, C. C. Fraenza, B. Itin, and S. Greenbaum, Journal of Molecular Liquids 329, 115454 (2021).[2] T. Chen, W. Kong, Z. Zhang, L. Wang, Y. Hu, G. Zhu, R. Chen, L. Ma, W. Yan, Y. Wang, J. Liu, and Z. Jin, Nano Energy 54, 17 (2018).

Enhancing Ionic Conductivity by in Situ Formation of Li7SiPS8/Argyrodite Hybrid Solid Electrolytes

Solid electrolytes (SEs) with high ionic conductivities are prerequisites to establish solid state batteries on a broad basis. Here we report a novel approach to thiophosphate SEs with improved ionic conductivities based on the in situ formation of LGPS-type tetra-Li7SiPS8/lithium argyrodite Li6PS5X (X= Cl, Br, I) hybrid SEs. Quantitative phase analysis reveals the formation of halogen-poor argyrodites Li6+yPS5+yX1–y next to the tetra-Li7SiPS8 majority phase and an amorphous side phase. EIS measurements indicate ionic conductivities of up to 7 mS cm–1, which exceed those of the parent tetra-Li7SiPS8 and Li6PS5X (X = Cl, Br, I) phases as well as those of simple physical mixtures whose conductivities are well described by the effective medium approximation. In contrast to previous reports, no evidence for halide substitution of the PS43– anions in tetra-Li7SiPS8 was found. Instead, the observed increase in ionic conductivity along with reduced grain boundary resistance is attributed to the directed growth of the tetra-Li7SiPS8 majority phase in the presence of an argyrodite side phase. As a result, a substantially increased isotropic Li diffusion radius is observed by PFG NMR, consistent with both more bulk-like Li transport within secondary particles and with reduced grain boundary resistance through more benign argyrodite interphases as compared to pristine tetra-Li7SiPS8. The microstructural changes induced by hybridization thus provide access to the bulk properties of tetra-Li7SiPS8.

Effect of Protein–Protein Interactions on Translational Diffusion of Spheroidal Proteins

One of the commonly accepted approaches to estimate protein–protein interactions (PPI) in aqueous solutions is the analysis of their translational diffusion. The present review article observes a phenomenological approach to analyze PPI effects via concentration dependencies of self- and collective translational diffusion coefficient for several spheroidal proteins derived from the pulsed field gradient NMR (PFG NMR) and dynamic light scattering (DLS), respectively. These proteins are rigid globular α-chymotrypsin (ChTr) and human serum albumin (HSA), and partly disordered α-casein (α-CN) and β-lactoglobulin (β-Lg). The PPI analysis enabled us to reveal the dominance of intermolecular repulsion at low ionic strength of solution (0.003–0.01 M) for all studied proteins. The increase in the ionic strength to 0.1–1.0 M leads to the screening of protein charges, resulting in the decrease of the protein electrostatic potential. The increase of the van der Waals potential for ChTr and α-CN characterizes their propensity towards unstable weak attractive interactions. The decrease of van der Waals interactions for β-Lg is probably associated with the formation of stable oligomers by this protein. The PPI, estimated with the help of interaction potential and idealized spherical molecular geometry, are in good agreement with experimental data.

Molecular and Artificial Neural Networks Modeling of Sorption and Diffusion of Small Alkanes, Alkenes and Their Ternary Mixtures in ZIF-8 at Different Temperatures.

Numerical computations comprising of Grand Canonical-Monte Carlo (GCMC) and Canonical Statistical Ensemble (NVT) Molecular Dynamics (MD) simulations were used to study the diffusion and sorption characteristics primarily for methane, ethane, and ethene molecules and for their ternary mixtures at different temperatures in ZIF-8 porous material. Methane as pure component or in mixture proved to be the sorbed hydrocarbon with the higher molecular mobility at the temperature range of 273-373 K among alkanes and alkenes. In addtion, alkenes were the hydrocarbons with the higher self-diffusion coefficients compared to the respective alkanes. In the ternary mixtures ethane was preferentially sorbed in ZIF-8 at all temperatures studied. Direct comparisons of the self-diffusivity data obtained from the NVT-MD simulations with recently reported Magic Angle Spinning Pulsed Field Gradient Nuclear Magnetic Resonance (MAS PFG NMR) measurements showed reasonable agreement. Furthermore, the NVT-MD self-diffusivity coefficients in conjunction with the aforementioned MAS PFG NMR experimental measurements, and sorption thermodynamic data obtained from the present GCMC simulations were utilized for the development of individual Artificial Neural Networks (ANNs) predictive modeling procedures in order to provide additional quantitative and qualitative information regarding the diffusion and sorption of small alkanes, alkenes in ZIF-8. The ANNs predictions were in good agreement with the experimental measurements and with the molecular simulation data. The modeling and analysis capabilities of ANNs along with their fast computations using moderate computer resources can significantly assist the irreplaceable molecular simulation and experimental approaches to cope with complicated problems at the molecular level.

Extending NMR Tortuosity Measurements to Paramagnetic Catalyst Materials Through the Use of Low Field NMR

Pulsed Field Gradient (PFG) NMR is recognised as an analytical technique used to characterise the tortuosity of porous media by measurement of the self-diffusion coefficient of a fluid contained within the pore space of the material of interest. Such measurements are usually performed on high magnetic field NMR hardware (>300 MHz). However, many materials of interest, in particular heterogeneous catalysts, contain significant amounts of paramagnetic species, which make such measurements impossible due to their characteristic short spin-spin relaxation times. Here it is demonstrated that by performing PFG NMR measurements on a low field magnet (2 MHz), tortuosity measurements can be obtained for a range of titania (TiO2) based carriers and catalyst precursors containing paramagnetic species up to a 20 wt.% loading. The approach is also used to compare the tortuosity of two catalyst precursors of the same metal loading prepared by different methods.

Engineering Advanced Environmentally Friendly Corrosion Inhibitors, Their Mechanisms, and Biological Effects in Live Zebrafish Embryos

Carbon steel is one of the most used construction materials and makes up the bulk of steel production in the world. However, this alloy is vulnerable to corrosion, which reduces its safety and costs trillions of dollars worldwide in terms of corrosion protection and infrastructure maintenance. Corrosion inhibitors are among the cheapest and most effective methods to minimize corrosion and maximize the shelf life of this ubiquitous alloy; however, they are often harmful to the environment. Currently there are no reports in terms of engineering design methodology to develop highly effective, advanced corrosion inhibitors. The possible synergistic behavior of a surface-active quaternary ammonium with a tailored carboxylate compound provides a rational molecular design toward delivering corrosion inhibitors to a metal surface through controlled speciation in solution. Here we show how entrapment and delivery of the anion inhibitor through speciation and micellar formation can lead to high inhibition efficiency, as determined by potentiodynamic polarization and electrochemical impedance spectroscopy. In particular, we demonstrate how NMR spectroscopy, pfg NMR diffusion measurements, and Cryo-TEM, taken together with molecular dynamic simulations, can reveal the micellar formation and its concentration dependence, with wormlike micelles evident at higher concentrations correlating with a dramatic increase in viscosity. This new organic corrosion inhibitor, cetrimonium 4-ethoxy cinnamate, provides significantly higher corrosion inhibition efficiency compared with the 4-hydroxy cinnamate analogue and with reduced toxic impact in the zebrafish embryo compared to the surface active CTAB often used as an antimicrobial.

Leipzig, Berlin and Hannover: Three Stations of a Beneficial Cooperation

AbstractThis essay looks back at the three stations of Jürgen Caro's career, starting with his time as a diploma student of Chemistry (1974–1975) and PhD student in the NMR laboratory (1975–1977) at the University of Leipzig, followed by his stay in Berlin at the Central Institute of Physical Chemistry and, afterwards, the newly founded Institute of Applied Chemistry and, finally, his appointment as full professor for Physical Chemistry at the Hannover University. The focus is on some of the results of our collaboration, including the use of PFG NMR and microimaging for in‐situ observation of diffusion in nanoporous materials and the useful application of these findings in the production of high‐performance membranes. Reference is also given to joint activities in science organization such as in European research networks and the Diffusion Fundamentals conference series of the Saxon Academy of Sciences and Humanities.

Hexagonal Mesoporous Silica for carbon capture: Unrevealing CO2 microscopic dynamics by Nuclear Magnetic Resonance

Global warming and environmental concerns have triggered global efforts to reduce anthropogenic carbon emission. Against this background, mesoporous silica materials have experienced a great expansion in the latest years due to their interesting carbon capture properties. Despite the very vast literature currently available in synthetic strategies and adsorption behaviour of MSs, the internal arrangement and diffusion properties of carbon dioxide (CO2) inside silica mesopores, to date, have been barely clarified. Here, mesoporous silica material with hexagonal framework (MCM-41) has been synthesized by a modified Stöber process, and its CO2 capture properties were assessed yielding a maximum amount of CO2 adsorbed of 18 wt% at 15 bar and RT. Fort the first time, microscopic distribution of CO2 and its mobility in the MCM-41 mesopores have been investigated by 13C NMR techniques. Peak fitting analysis of the 13C NMR spectra and T1-relaxometry data revealed a multiple component configuration for CO2 adsorbed in the silica mesopores with at least two physisorbed species coexisting. 13C PFG NMR self-diffusion study showed anisotropic long-range mobility for carbon dioxide adsorbed in MCM-41. The fastest self-diffusion coefficient, ascribed CO2 molecules diffusing parallel to the axis of the MCM-41 channels, was in the order of 10−5 cm2 s-1, i.e., two order of magnitude higher that of gas diffusing perpendicular to the mesopore. This study is crucial to properly address the future design and preparation of mesoporous silica materials with improved CO2 capture performances.

Role of a Multivalent Ion-Solvent Interaction on Restricted Mg2+ Diffusion in Dimethoxyethane Electrolytes.

The diffusion behavior of Mg2+ in electrolytes is not as readily accessible as that from Li+ or Na+ utilizing PFG NMR, due to the low sensitivity, poor resolution, and rapid relaxation encountered when attempting 25Mg NMR. In MgTFSI2/DME solutions, "bound" DME (coordinating to Mg2+) and "free" DME (bulk) are distinguishable from 1H NMR. With the exchange rates between them obtained from 2D 1H EXSY NMR, we can extract the self-diffusivities of free DME and bound DME (which are equal to that of Mg2+) before the exchange occurs using PFG diffusion NMR measurements coupled with analytical formulas describing diffusion under two-site exchange. The high activation enthalpy for exhange (65-70 kJ/mol) can be explained by the structural change of bound DME as evidenced by its reduced C-H bond length. Comparison of the diffusion behaviors of Mg2+, TFSI-, DME, and Li+ reveals a relative restriction to Mg2+ diffusion that is caused by the long-range interaction between Mg2+ and solvent molecules, especially those with suppressed motions at high concentrations and low temperatures.

Molecular Assembly in Block Copolymer-Surfactant Nanoparticle Dispersions: Information on Molecular Exchange and Apparent Solubility from High-Resolution and PFG NMR.

Internally structured block copolymer-surfactant particles are formed when the complex salts of ionic-neutral block copolymers neutralized by surfactant counterions are dispersed in aqueous media. Here, we report the 1H NMR signal intensities and self-diffusion coefficients (D, from pulsed field gradient nuclear magnetic resonance, PFG NMR) of trimethyl alkylammonium surfactant ions and the poly(acrylamide)-block-poly(acrylate) (PAAm-b-PA) polyions forming such particles. The results reveal the presence of an “NMR-invisible” (slowly exchanging) fraction of aggregated surfactant ions in the particle core and an “NMR-visible” fraction consisting of surface surfactant ions in rapid exchange with the surfactant ions dissociated into the aqueous domain. They also confirm that the neutral PAAm blocks are exposed to water at the particle surface, while the PA blocks are buried in the particle core. The self-diffusion of the polyions closely agree with the self-diffusion of a hydrophobic probe molecule solubilized in the particles, showing that essentially all copolymer chains are incorporated in the aggregates. Through centrifugation, we prepared macroscopically phase-separated systems with a phase concentrated in particles separated from a clear dilute phase. D values for the surfactant and block copolymer indicated that the dilute phase contained small aggregates (ca. 5 nm) of surfactant ions and a few anionic-neutral block copolymer chains. Regardless of the overall concentration of the sample, the fraction of block copolymer found in the dilute phase was nearly constant. This indicates that the dilute fraction represented a tail of small particles created by the dispersion process rather than a true thermodynamic solubility of the complex salts.

The Role of Rotational Motion in Diffusion NMR Experiments on Supramolecular Assemblies: Application to Sup35NM Fibrils

AbstractPulsed‐field gradient (PFG) NMR is an important tool for characterization of biomolecules and supramolecular assemblies. However, for micrometer‐sized objects, such as amyloid fibrils, these experiments become difficult to interpret because in addition to translational diffusion they are also sensitive to rotational diffusion. We have constructed a mathematical theory describing the outcome of PFG NMR experiments on rod‐like fibrils. To test its validity, we have studied the fibrils formed by Sup35NM segment of the prion protein Sup35. The interpretation of the PFG NMR data in this system is fully consistent with the evidence from electron microscopy. Contrary to some previously expressed views, the signals originating from disordered regions in the fibrils can be readily differentiated from the similar signals representing small soluble species (e.g. proteolytic fragments). This paves the way for diffusion‐sorted NMR experiments on complex amyloidogenic samples.

A Study of Ferrocene Diffusion in Toluene/Tween 20/1-Butanol/Water Microemulsions for Redox Flow Battery Applications

Redox flow batteries (RFBs) possess multiple advantages as a flexible energy storage solution. However, RFB researchers are still facing many challenges in finding an appropriate electrolyte. Microemulsions have recently been proposed as a promising alternative RFB electrolyte because of their ability to accommodate organic redox species with fast electron transfer rates that are not soluble in aqueous phase, while still offering the high conductivity of an aqueous salt electrolyte. In this work, we focused on understanding the transport of ferrocene (Fc) in a toluene/Tween 20/1-butanol/water model microemulsion and studied the compositional influence on Fc diffusion. The results show that Fc redistributes among the oil, surfactant, and water microenvironments, and the corresponding diffusion and partition coefficients are quantified. Thus, a tortuous path diffusion model is proposed to describe the mass transport of Fc to an electrode surface. Diffusion coefficients are also obtained by pulsed-field gradient nuclear magnetic resonance (PFG NMR), while the values for Fc diffusion are substantially higher than those from electrochemical measurements, suggesting that they measure samples in different ways. The current contributions from each microenvironment indicate that the Fc permeability is much higher in the oil, even though the electron transfer reaction is likely occurring in the surfactant.

Mg2+ Solvation Structures and Diffusion Properties in Dimethoxyethane Solutions Using Multimodal NMR Analysis

Mg-based secondary battery systems represent a promising advancement over current technology, however a detailed molecular view of the battery components are lacking which prevents the implementation of such technologies. Diffusion behaviors of Mg2+ in electrolytes are usually not as readily accessible as Li+ and Na+ through PFG NMR, due to the low sensitivity and resolution of 25Mg NMR. Herein, we report the evolution of solvation structures and diffusion behaviors in the traditional MgTFSI2/DME based electrolyte using quantitative multinuclear (1H, 19F, 17O) NMR, NMR relaxation, 2D 1H EXSY NMR, as well as PFG diffusion measurements. High resolution 1H NMR reveals bound DME (DME molecules coordinating to Mg2+) and bulk DME (“free” diffusing DME) within solution structure, where the diffusion of bound DME provides informatin about Mg2+ diffusion through a two-site exchange-diffusion model. We concluded that the dominant solvation structure evolves from contact ion pairs (i.e. [Mg(TFSI)(DME)1-2]+) to fully solvated clusters (i.e. [Mg(DME)3]2+) as salt concentration increases or as temperature decreases. This transition is coupled to a phase separation between 0.06 M and 0.36 M. Subsequent analysis is based on an explanation of the solvent rearrangement process and the competition between solvent molecules and TFSI anions for cation coordination. Furthermore, the comparison between diffusion behaviros of Mg2+ and TFSI- reveals the formation of supercluster structures that highly constrain Mg2+ diffusion at high concentrations and low temperatures but present little restricticiton to TFSI- diffusion, properbly due to the long-distance effect of multivalent Mg2+ on DME with suppressed motion under these conditions.

Molecular and Ionic Diffusion in Ion Exchange Membranes and Biological Systems (Cells and Proteins) Studied by NMR.

The results of NMR, and especially pulsed field gradient NMR (PFG NMR) investigations, are summarized. Pulsed field gradient NMR technique makes it possible to investigate directly the partial self-diffusion processes in spatial scales from tenth micron to millimeters. Modern NMR spectrometer diffusive units enable to measure self-diffusion coefficients from 10−13 m2/s to 10−8 m2/s in different materials on 1 H, 2 H, 7 Li, 13 C, 19 F, 23 Na, 31 P, 133 Cs nuclei. PFG NMR became the method of choice for reveals of transport mechanism in polymeric electrolytes for lithium batteries and fuel cells. Second wide field of application this technique is the exchange processes and lateral diffusion in biological cells as well as molecular association of proteins. In this case a permeability, cell size, and associate lifetime could be estimated. The authors have presented the review of their research carried out in Karpov Institute of Physical Chemistry, Moscow, Russia; Institute of Problems of Chemical Physics RAS, Chernogolovka, Russia; Kazan Federal University, Kazan, Russia; Korea University, Seoul, South Korea; Yokohama National University, Yokohama, Japan. The results of water molecule and Li+, Na+, Cs+ cation self-diffusion in Nafion membranes and membranes based on sulfonated polystyrene, water (and water soluble) fullerene derivative permeability in RBC, casein molecule association have being discussed.

PFG NMR time-dependent diffusion coefficient analysis of confined emulsion: Post drainage phase conformation

In this work, we present a characterization of phase configuration in water-saturated sintered glass bead samples after oil injection, through the analysis of time-dependent diffusion coefficients obtained from sets of one-dimensional pulsed field gradient nuclear magnetic resonance (PFG NMR) measurements, pre and post drainage. Estimates of samples' surface-to-volume ratio and permeability from pre drainage PFG measurements in a water-saturated sample were compared with analytical and reported values, respectively, and a fair agreement was found in both cases. Short-time analysis of diffusion coefficients extracted from PFG measurements was used to quantify the increase in surface-to-volume ratio probed by the wetting phase after drainage. Analysis of water and oil diffusion coefficients from post drainage PFG experiments were carried out using a bi-Gaussian model, and two distinct scenarios were considered to describe fluids conformation within pores. For the case where non-wetting phase was considered to exhibit a poorly connected geometry, an analysis assuming the formation of oil-in-water droplets within pores was performed, and a Gaussian distribution of droplets radii was determined.

Impact of intermolecular attraction and repulsion on molecular diffusion and virial coefficients of spheroidal and rod-shaped proteins

Recognition of protein intermolecular interactions is a key factor for the study and manipulation of protein activity in living systems and biotechnology formulations. Experimental parameter that is sensitive to intermolecular interactions is molecular diffusion. This work presents an extension of an earlier work where we proposed the complementary use of pulsed field gradient nuclear magnetic resonance (PFG NMR) and dynamic light scattering (DLS) to study the specific features of intermolecular interactions via protein translational diffusion. PFG NMR methodology characterizes the thermal motion of protein by means of the self-diffusion coefficient and friction formalism. DLS experiments provide the protein collective (or mutual) diffusion coefficient, which evaluates the direct, non-specific intermolecular interactions of proteins by means of virial coefficients. Theoretical analysis of obtained experimental diffusion data is based on the combination of the friction formalism of nonequilibrium thermodynamics (Vink approach) with the Deryaguin-Landau-Verwey-Overbeek (DLVO) theory. To evaluate the electrostatic potential of proteins with different shape - spheroidal alfa-chymotrypsin (ChTr) and the rod-shaped fibrinogen (Fg) we applied the model of “porous” colloid particles. Our analysis has shown that the atypical local decrease of collective diffusion relative to self-diffusion is a consequence of the dominance of van der Waals attraction over electrostatic repulsion for the rod-shaped Fg.

Determination of Binary Diffusivities in Concentrated Lithium Battery Electrolytes via NMR and Conductivity Measurements

We report on the experimental determination of Onsager–Stefan–Maxwell binary diffusivities using the pulsed-field gradient nuclear magnetic resonance (PFG NMR) technique, which are required for the...

Structural and Ion Dynamics in Fluorine-Free Oligoether Carboxylate Ionic Liquid-Based Electrolytes.

Here, we investigate the physicochemical and electrochemical properties of fluorine-free ionic liquid (IL)-based electrolytes with two different cations, tetrabutylphosphonium, (P4,4,4,4)+, and tetrabutylammonium, (N4,4,4,4)+, coupled to a new anion, 2-[2-(2-methoxyethoxy)ethoxy]acetate anion (MEEA)−, for both neat and (P4,4,4,4)(MEEA) also doped with 10–40 mol % of Li(MEEA). We find relatively weaker cation–anion interactions in (P4,4,4,4)(MEEA) than in (N4,4,4,4)(MEEA), and for both ILs, the structural flexibility of the oligoether functionality in the anion results in low glass transition temperatures, also for the electrolytes made. The pulsed field gradient nuclear magnetic resonance (PFG NMR) data suggest faster diffusion of the (MEEA)− anion than (P4,4,4,4)+ cation in the neat IL, but the addition of a Li salt results in slightly lower mobility of the former than the latter and lower ionic conductivity. This agrees with the combined 7Li NMR and attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy data, which unambiguously reveal preferential interactions between the lithium cations and the carboxylate groups of the IL anions, which also increased as a function of the lithium salt concentration. In total, these systems provide a stepping stone for further design of fluorine-free and low glass transition temperature IL-based electrolytes and also stress how crucial it is to control the strength of ion–ion interactions.

Effect of sintering temperature on Li diffusivity in Li0.29La0.57TiO3: Local hopping and long-range transport

The influence of sintering temperature on Li diffusivity was investigated for two Li0.29La0.57TiO3 samples sintered at 1400 °C and 1450 °C, respectively. Synchrotron radiation diffraction was used to get detailed insights into the crystal structure and the real structure and also into the subtle differences between the two samples. 7Li NMR relaxometry and 7Li PFG NMR were used to observe the local hopping of Li ions and the long-range transport, respectively. Our results show that the motion of Li ions inside the crystallites is very similar for both samples. The enhanced conductivity of the sample sintered at the higher temperature, as observed by impedance spectroscopy, is caused by the reduced density of grain boundaries.