Magnetic Resonance Spin-lattice Relaxation Research Articles

The novel oxy-sulfide glassy ionic conductors Na4P2S7-xOx 0 ≤ x ≤ 7: Understanding the features of static and dynamic cations

We present a 23Na nuclear spin dynamics model for interpreting nuclear magnetic resonance (NMR) spin-lattice relaxation and central linewidth data in the invert glass system Na4P2S7-xOx, 0 ≤ x ≤ 7. The glassy nature of this material results in variations in local Na+ cation environments that may be described by a Gaussian distribution of activation energies. A consistent difference between the mean activation energies determined by NMR and DC conductivity measurements was observed, and interpreted using a percolation theory model. From this, the NaNa coordination number in the sodium cation sublattice was obtained. These values were consistent with jumps through tetrahedral faces of the sodium cages for the sulfur rich glasses, x < 5, consistent with proposed models of their short range order (SRO) structures. From NMR spin-echo measurements, we determined the NaNa second moment M2 resulting from the NaNa magnetic dipole interaction of nearest neighbors. Values of M2 obtained as a function of sodium number density N were in agreement with models for uniform sodium distribution, indicating that these invert glass systems form so as to maximize the average NaNa distance. A simple Coulombic attraction model between Na+ cation and X (=S−, O−) anion was applied to calculate the activation energy. In the range 1.5 ≤ x ≤ 7, an increase in activation energy with increasing oxygen content x occurred, and was consistent with the decrease in average anionic radius, and the increase in Coulombic attraction. For small oxygen additions, 0 ≤ x ≤ 1.5, the suggested minimum at low oxygen concentration seen in the activation energies obtained from DC conductivity data is not evident in the model.

Nuclear spin relaxation in aqueous paramagnetic ion solutions.

A Brownian shell model describing the random rotational motion of a spherical shell of uniform particle density is presented and validated by molecular dynamics simulations. The model is applied to proton spin rotation in aqueous paramagnetic ion complexes to yield an expression for the Larmor-frequency-dependent nuclear magnetic resonance spin-lattice relaxation rate T_{1}^{-1}(ω) describing the dipolar coupling of the nuclear spin of the proton with the electronic spin of the ion. The Brownian shell model provides a significant enhancement to existing particle-particle dipolar models without added complexity, allowing fits to experimental T_{1}^{-1}(ω) dispersion curves without arbitrary scaling parameters. The model is successfully applied to measurements of T_{1}^{-1}(ω) from aqueous manganese(II), iron(III), and copper(II) systems where the scalar coupling contribution is known to be small. Appropriate combinations of Brownian shell and translational diffusion models, representing the inner and outer sphere relaxation contributions, respectively, are shown to provide excellent fits. Quantitative fits are obtained to the full dispersion curve of each aquoion with just five fit parameters, with the distance and time parameters each taking a physically justifiable numerical value.

Structural geometry and molecular dynamics of hybrid organic–inorganic [NH3(CH2)6NH3]CdCl4 crystals close to phase transition temperatures

Organic–inorganic hybrid perovskites are highly promising for application in various electrochemical devices, such as batteries and fuel cells. The physical properties of crystals of the organic–inorganic hybrid perovskite [NH3(CH2)6NH3]CdCl4 are important for their future application. Therefore, these crystals were grown and their phase transition temperatures TC1 = 337 K and TC2 = 472 K were determined using powder X-ray diffraction and differential scanning calorimetry. We observed that the crystallographic surroundings of 1H and 13C in the cation near TC1 did not show significant changes, whereas those of 113Cd in the anion changed significantly. The change in the coordination geometry of C1 around Cd near TC1 changed the N–H···Cl bond by connecting with the 1H of NH3. The nuclear magnetic resonance spin-lattice relaxation time T1ρ suggested that the 1H energy transfer processes in phases III and II were easier, whereas the 13C energy transfer processes were easier in phase III than in phase II. The results of the current study for [NH3(CH2)nNH3]CdCl4 (n = 6) were compared with those for n = 2, 3, 4, and 5 obtained from previous studies. The features of the length of CH2 and even–odd number of carbons in the diammonium chain are expected to facilitate potential applications in the future.

Relative Cation-Anion Diffusion in Alkyltriethylammonium-Based Ionic Liquids.

19F Nuclear Magnetic Resonance spin-lattice relaxation experiments have been performed for a series of ionic liquids including the same anion, bis(trifluoromethanesulfonyl)imide, and cations with alkyl chains of different lengths: triethylhexylammonium, triethyloctylammonium, decyltriethylammonium, dodecyltriethylammonium, decyltriethylammonium, and hexadecyltriethylammonium. The experiments have been carried out in a frequency range of 10 kHz to 10 MHz versus temperature. A thorough analysis of the relaxation data has led to the determination of the cation–anion as a relative translation diffusion coefficient. The diffusion coefficients have been compared with the corresponding cation–cation and anion–anion diffusion coefficients, revealing a correlation in the relative translation movement of the anion and the triethylhexylammonium, triethyloctylammonium, decyltriethylammonium, and dodecyltriethylammonium cations, whereas the relative translation diffusion between the anion and the cations with the longer alkyl chains, decyltriethylammonium and hexadecyltriethylammonium, remains rather uncorrelated (correlated to a much lesser extent).

Molecular motion of imidazolium cations and phase transitions in (ImH)2KCo(CN)6 with double perovskite structure

Temperature dependence of 1H nuclear magnetic resonance spin–lattice relaxation time T1 of (ImH)2KCo(CN)6, ImH+: imidazolium cation, is reported. The asymmetric T1 minimum observed in intermediate-temperature phase between 198 and 112 K is analyzed assuming the Cole-Davidson distribution of correlation time. Temperature dependences of 14N nuclear quadrupole resonance frequencies and spin–lattice relaxation times are also reported. The phase transitions at 198 and 112 K are shown to be of second and first order, respectively. The 14N relaxation is shown to be governed by the electric field gradient fluctuation due to the in-plane reorientational motion of the imidazolium cations.

Characterization of Ion Association and Solvation in NaPF6 Carbonate Electrolytes

In this work we aimed to determine the ions association and solvation in electrolytes comprised of NaPF6 in binary EC:PC, and ternary 5EC:3PC:2DEC carbonate solvents. We studied their local and bulk transport properties through multi-Nuclear (1H, 19F and 23Na) Magnetic Resonance spin-lattice relaxation time (T1 ) and self-diffusion coefficient (D) measurements. These studies were complemented with ionic conductivity and solution viscosity measurements. Results show several interesting features. Firstly, the Walden Product – which relates the molar conductivity and viscosity through a temperature-dependent constant – showed a dependence on temperature (see Figure 1). This suggested the dissociation of NaPF6 is dependent on temperature and is lower for the less polar electrolytes. Secondly, the sodium ions are preferentially solvated by PC molecules over EC. Thirdly, significant cation-anion association was observed for the less polar electrolytes. Lastly, this association was independent of temperature indicating that the temperature dependence of the Walden Product is primarily due to that of the viscosity. These results can aid in the improvement of ‘beyond lithium ion’ electrolytes for energy storage applications. Figure 1

2H NMR study on temperature-dependent water dynamics in amino-acid functionalized silica nanopores.

We prepare various amino-acid functionalized silica pores with diameters of ∼6 nm and study the temperature-dependent reorientation dynamics of water in these confinements. Specifically, we link basic Lys, neutral Ala, and acidic Glu to the inner surfaces and combine 2H nuclear magnetic resonance spin-lattice relaxation and line shape analyses to disentangle the rotational motions of the surfaces groups and the crystalline and liquid water fractions coexisting below partial freezing. Unlike the crystalline phase, the liquid phase shows reorientation dynamics, which strongly depends on the chemistry of the inner surfaces. The water reorientation is slowest for the Lys functionalization, followed by Ala and Glu and, finally, the native silica pores. In total, the rotational correlation times of water at the different surfaces vary by about two orders of magnitude, where this span is largely independent of the temperature in the range ∼200-250 K.

Transport studies of NaPF6 carbonate solvents-based sodium ion electrolytes

Characterizing fundamental ion transport is necessary for the modification and development of electrolytes. In this study, we investigated the local and bulk transport properties of 1 M NaPF6 in the binary EC:PC (1:1), and ternary 5EC:3PC:2DEC (5:3:2) solvents, as well as their 2 wt.% FEC modulated versions. We determined 1H, 19F and 23Na Nuclear Magnetic Resonance (NMR) spin-lattice relaxation time (T1), self-diffusion coefficient (D), linewidth and chemical shift. These were complimented with density, viscosity and ionic conductivity measurements, all as a function of temperature. Both the viscosity and ionic conductivity displayed VFT behavior and their Walden products showed a dependence on temperature. This coupled with their having the lower Walden products indicated less salt dissociation in the 5EC:3PC:2DEC and 5EC:3PC:2DEC + 2 wt.% electrolytes. NMR D19F and 23Na values for these electrolytes were also similar at 298K indicating cation-anion association, but diverged with increasing temperatures, with that for the anion being greater than the cation. The addition of the FEC provides greater local dynamics for the individual solvents in the less polar electrolyte but appeared to impede that of the ions.

Nuclear magnetic resonance spin-lattice relaxation of lithium ions in aqueous solution by NMR and molecular dynamics.

We study the aqueous solvation dynamics of lithium ions using nuclear magnetic resonance spectroscopy, molecular dynamics, and viscosity measurements. Several relaxation mechanisms are examined to explain the strong increases of spin-lattice relaxation toward high concentrations. The use of both 6Li and 7Li isotopes is helpful to identify the quadrupolar contribution to the relaxation rate. In particular, it is found that the quadrupolar interaction constitutes the strongest contribution above a concentration of ∼10 molal. The next-strongest contribution arises from interactions that scale with the square of the gyromagnetic ratio (mostly the dipolar interaction), and the experimental relaxation rates appear to be fully accounted for when these mechanisms are combined over the concentration range up to the saturation concentration. The study of solvation dynamics, particularly at high concentrations, could be of relevance for electrolyte dynamics in aqueous Li-ion rechargeable batteries.

Continuous Matrix Product Operator Approach to Finite Temperature Quantum States.

We present an algorithm for studying quantum systems at finite temperature using continuous matrix product operator representation. The approach handles both short-range and long-range interactions in the thermodynamic limit without incurring any time discretization error. Moreover, the approach provides direct access to physical observables including the specific heat, local susceptibility, and local spectral functions. After verifying the method using the prototypical quantum XXZ chains, we apply it to quantum Ising models with power-law decaying interactions and on the infinite cylinder, respectively. The approach offers predictions that are relevant to experiments in quantum simulators and the nuclear magnetic resonance spin-lattice relaxation rate.

Clinical assessment of adenosine stress and rest cardiac magnetic resonance T1 mapping for detecting ischemic and infarcted myocardium

Cardiac magnetic resonance (CMR) spin-lattice relaxation time (T1) may be influenced by pathologic conditions due to changes in myocardial water content. We aimed to validate the principle and investigate T1 mapping at rest and adenosine stress to differentiate ischemic and infarcted myocardium from controls. Patients with suspected coronary artery disease who underwent CMR were prospectively recruited. Native rest and adenosine stress T1 maps were obtained using standard modified Look-Locker Inversion-Recovery technique. Among 181 patients included, T1 values were measured from three groups. In the control group, 72 patients showed myocardium with a T1 profile of 1,039 ± 75 ms at rest and a significant increase during stress (4.79 ± 3.14%, p < 0.001). While the ischemic (51 patients) and infarcted (58 patients) groups showed elevated resting T1 compared to controls (1,040 ± 90 ms for ischemic; 1,239 ± 121 ms for infarcted, p < 0.001), neither of which presented significant T1 reactivity (1.38 ± 3.02% for ischemic; 1.55 ± 5.25% for infarcted). We concluded that adenosine stress and rest T1 mapping may be useful to differentiate normal, ischemic and infarcted myocardium.

Lithium-Ion Transport in Nanocrystalline Spinel-Type Li[InxLiy]Br4 as Seen by Conductivity Spectroscopy and NMR.

Currently, a variety of solid Li+ conductors are being discussed that could potentially serve as electrolytes in all-solid-state Li-ion batteries and batteries using metallic Li as the anode. Besides oxides, sulfides and thioposphates, and also halogenides, such as Li3YBr6, belong to the group of such promising materials. Here, we report on the mechanosynthesis of ternary, nanocrystalline (defect-rich) Li[InxLiy]Br4, which crystallizes with a spinel structure. We took advantage of a soft mechanochemical synthesis route that overcomes the limitations of classical solid-state routes, which usually require high temperatures to prepare the product. X-ray powder diffraction, combined with Rietveld analysis, was used to collect initial information about the crystal structure; it turned out that the lithium indium bromide prepared adopts cubic symmetry (). The overall and electronic conductivity were examined via broadband conductivity spectroscopy and electrical polarization measurements. While electric modulus spectroscopy yielded information on long-range ion transport, 7Li nuclear magnetic resonance (NMR) spin-lattice relaxation measurements revealed rapid, localized ionic hopping processes in the ternary bromide. Finally, we studied the influence of thermal treatment on overall conductivity, as the indium bromide might find applications in cells that are operated at high temperatures (330 K and above).

Motional freedom of dimethylammonium ions in a cyanoelpasolite, [(CH3)2NH2]2KCo(CN)6, which exhibits phase transition associated with a distinct change in dielectric property.

The temperature dependence of the 1H nuclear magnetic resonance spin-lattice relaxation time T1 of [(CH3)2NH2]2KCo(CN)6 and the partially deuterated analogue [(CD3)2NH2]2KCo(CN)6 has been reported. A change in the molecular motion of organic cations through the first-order phase transition at Tc = 246 K has been discussed. Although this first-order transition has been reported as an isosymmetric transition, in which the space group of the crystal does not change, the number of the 14N nuclear quadrupole resonance line changed from three in the high-temperature phase to twelve in the low-temperature phase indicating the lowering of crystal symmetry.

Concomitant Polymorphism in an Organic Solid: Molecular and Crystal Structure and Intra- and Intermolecular Potential Contributions to tert-Butyl and Methyl Group Rotation.

We investigate the relationship between structure (crystal and molecular) and tert-butyl and methyl group dynamics in 2-(tert-butyl)-9-(4-(tert-butyl)phenyl)anthracene. Powder and single-crystal X-ray diffraction, taken together, show that different polycrystalline samples recrystallized from different solvents have different amounts of at least four polymorphs (crystallites having different crystal structures), of which we have identified three by single crystal X-ray diffraction. The molecules in the asymmetric units of the different crystal structures differ by the dihedral angle the tert-butylphenyl group makes with the anthracene moiety. Ab initio electronic structure calculations on the isolated molecule show that very little intramolecular energy is required to change this angle over a range of about 60° which is probably the origin of the concomitant polymorphism (crystals of more than one polymorph in a polycrystalline sample). Solid state 1 H nuclear magnetic resonance (NMR) spin-lattice relaxation experiments support the powder and single-crystal X-ray results and provide average NMR activation energies (closely related to rotational barriers) for the rotation of the tert-butyl groups and their constituent methyl groups. These barriers have both an intramolecular and an intermolecular component. The latter is sensitive to the crystal structure. The intramolecular components of the rotational barriers of the two tert-butyl groups in the isolated molecule are investigated with ab initio electronic structure calculations.

Ion dynamics in Al-Stabilized Li7La3Zr2O12 single crystals – Macroscopic transport and the elementary steps of ion hopping

Li7La3Zr2O12 (LLZO) garnet-type ceramics are considered as very promising candidates for solid electrolytes and have been extensively studied in the past few years. Several studies report on an increase in ionic conductivity by doping with ions, such as Al3+ and Ga3+, to stabilize the cubic modification of LLZO. Unfortunately, so far ion dynamics have mainly been studied using powdered samples. Such studies may suffer from chemical heterogeneities concerning Al distribution. Here, we took advantage of Al-stabilized LLZO single crystals to throw light on the elementary steps of ion hopping. We used 7Li nuclear magnetic resonance (NMR) spin-lattice relaxation measurements and conductivity spectroscopy to probe dynamic parameters from both a microscopic and macroscopic point of view. At 293 K the total conductivity turned out to be 0.082 mS cm−1, which is remarkably good for LLZO exhibiting an Al-content of only 0.37 wt%. Most importantly, 7Li NMR spin-lock transients revealed two overlapping diffusion-induced processes. Overall, activation energies from spin-lock NMR excellently agree with that from conductivity measurements; both techniques yield values around 0.36 eV. The corresponding diffusion coefficients deduced from NMR and conductivity measurements almost coincide. The magnetic spin fluctuations sensed by NMR provide an in-depth look at the elementary jump processes, which can barely be revealed by macroscopic impedance spectroscopy providing average values. In particular, we were able to precisely measure the local hopping barrier (0.20 eV) characterizing forward-backward jumps between the sites 24d and 96h.

Investigating the Internal Processes of Thermo-Electrochemical Cells Using in-Situ Magnetic Resonance Imaging

Thermo-electrochemical cells are emerging as a promising and efficient method to convert waste heat to electricity. In addition to developing novel redox electrolyte materials to increase the energy densities, it is crucial for future developments to understand the internal chemical and thermodynamical processes happening inside the thermo-electrochemical cell while it is under operating conditions. Although the temperature and concentration distributions between the electrodes and the variations of the convection currents with cell orientation have been modelled mathematically, it has been a challenge to study these internal processes using experimental techniques. Magnetic resonance imaging (MRI) is a non-invasive and well-established diagnosis technique in medical research to investigate physiology, but it also has the capability to study spatial properties of materials, chemical and thermodynamic processes in energy storage devices using different image contrast options including spin density, relaxation time and velocity [1]. The goals of this study are to develop an MRI method to study the internal chemical and thermodynamic processes within a functioning thermo-electrochemical cell, and understanding how these are affected by the electrolyte, the cell geometry and the orientation of the thermal gradient. A cobalt redox couple based electrolyte, which has been shown to be a promising candidate for thermo-electrochemical cells [2], was used for the in-situ experiments inside specialised cells custom built for MRI experiments, and temperature and concentration dependent 1H nuclear magnetic resonance spin-lattice relaxation time (T1) measurements were used to interpret the 1H T1 weighted MRI images of the working cells.

Numerical study of the temperature dependence of the NMR relaxation rate across the superfluid–Bose glass transition in one dimension

We study the nuclear magnetic resonance (NMR) spin-lattice relaxation rate $1/T_1$ in random one-dimensional spin chains as function of the temperature and disorder strength. In the zero temperature limit, the system displays a disorder-induced quantum phase transition between a critical Tomonaga-Luttinger liquid (TLL) phase and a localized Bose glass phase. The $1/T_1$ is investigated across this transition using large-scale simulations based on matrix product state techniques. We find that this quantity can detect the transition and probe the value of the dimensionless TLL parameter $K$. We also compute the NMR relaxation rate distributions for each temperature and disorder strength considered. In particular we discuss the applicability of the stretched exponential fit to the return-to-equilibrium function in order to extract the $1/T_1$ experimentally. The results presented here should provide valuable insights in regards of future NMR experiments in realistic disordered spin compounds.

Imaging of nuclear magnetic resonance spin-lattice relaxation activation energy in cartilage.

Samples of human and bovine cartilage have been examined using magnetic resonance imaging to determine the proton nuclear magnetic resonance spin–lattice relaxation time, T1, as a function of depth within through the cartilage tissue. T1 was measured at five to seven temperatures between 8 and 38°C. From this, it is shown that the T1 relaxation time is well described by Arrhenius-type behaviour and the activation energy of the relaxation process is quantified. The activation energy within the cartilage is approximately 11 ± 2 kJ mol−1 with this notably being less than that for both pure water (16.6 ± 0.4 kJ mol−1) and the phosphate-buffered solution in which the cartilage was immersed (14.7 ± 1.0 kJ mol−1). It is shown that this activation energy increases as a function of depth in the cartilage. It is known that cartilage composition varies with depth, and hence, these results have been interpreted in terms of the structure within the cartilage tissue and the association of the water with the macromolecular constituents of the cartilage.

NMR Characterization of the Na+ Ion Transport in Mixed Ionic Liquids Electrolytes

In the market of medium- and large- scale energy supplies, sodium (Na+) ion batteries are considered a possible alternative to current technologies. This is because sodium is naturally more abundant and cheaper than the ubiquitous lithium. Room temperature Na+ batteries typically employ organic solvents such as propylene carbonate. However, room temperature ionic liquids – while more viscous – are safer, and because of this attention is being paid towards their partial or complete replacement of organic solvents. Towards this endeavor, we investigated ions dynamics in mixtures of varying concentrations of sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) or sodium bis(fluorosulfonyl)imide (NaFSI) salts, combined with the 1-butyl-1-methylpyrrolidinium (PYR1,4) FSI and PYR1,4 TFSI ionic liquids. We used variable-temperature 1H and 23Na Nuclear Magnetic Resonance (NMR) spin-lattice relaxation times (T1) and self-diffusion coefficients (D) measurements to investigate the short- and long- range ions dynamics and a preview of or results are shown in Figure 1. Both T1 (1H and 23Na) and 1H D data show greater short- and long- range dynamics for mixtures containing the FSI salt or ionic liquid. A more comprehensive discussion will be presented. Figure 1. Variable-temperature Na+ spin-lattice relaxation times (left) and 1H self-diffusion coefficients (right) for mixtures of various mol% of NaFSI or NaTFSI salt with PYR1,4 based ILs. Figure 1

Ion dynamics in a new class of materials: nanoglassy lithium alumosilicates

In many cases nanocrystalline materials, prepared through high-energy ball milling, reveal enhanced ion dynamics when compared to the situation in the coarse-grained analogues. This effect, which has particularly been seen for lithium alumosilicates, has been ascribed to structural disorder, i.e., the introduction of defect sites during mechanical treatment. Much less is, however, known about ion transport in nanostructured amorphous materials, e.g., nanoglassy compounds, which are regarded as a new class of functional materials. Following earlier studies on nanoglassy lithium alumosilicates and borates, here we studied ion dynamics in nanoglassy petalite LiAlSi4O10. While conductivity spectroscopy unequivocally reveals that long-range ion dynamics in nanoglassy LiAlSi4O10 decreases upon milling, local dynamics, sensed by 7Li nuclear magnetic resonance (NMR) spin-lattice relaxation, points to enhanced Li ion mobility compared to the non-treated glass. Most likely, as for nanocrystalline ceramics also for nanoglassy samples a heterogeneous structure, consisting of bulk and interfacial regions, is formed. For LiAlSi4O10 these interfacial regions, characterized by a higher degree of free volume, might act as hosts for spins experiencing fast longitudinal NMR relaxation. Obviously, these regions do not form a through-going network, which would allow the ions to move over long distances as quickly as in the unmilled glass.