Search

Fundamental studies of the materials with fast sodium mobility are important for the development of energy storage systems. This article presents the results of experimental studies of Na-conducting oxide Na9In(MoO4)6. This compound crystallizes in rhombohedral symmetry with the space group R $$\overline{3}$$ c and the unit cell parameters: a = 15.08695(6) and c = 19.1701(2) A. Impedance spectroscopy measurements show that Na9In(MoO4)6 is an ionic conductor with a conductivity of about 2.1 × 10−2 Sm·cm−1 at 803 K. The 23Na NMR data reveal the coexistence of three types of sodium motion. These motional processes are activated at different temperatures and are characterized by substantially different nature and dynamics characteristics.

The rechargeable Na-ion batteries attract much attention as an alternative to the widely used but expensive Li-ion batteries. The search for materials with high sodium diffusion is important for the development of solid state electrolytes. We present the results of experimental and ab initio studies of the Na-ion diffusion mechanism in Na9Sc(MoO4)6. The ion conductivity reaches the value of 3.6 × 10−2 S cm−1 at T ∼ 850 K. The 23Na and 45Sc NMR data reveal the coexistence of three different types of Na-ion motion in the temperature range from 300 to 750 K. They are activated at different temperatures and are characterized by substantially different dynamics parameters. These features are confirmed by ab initio calculations of activation barriers for sodium diffusion along various paths.

Driven by the rise of the electric automotive industry, the Li-ion battery market is in strong expansion. This technology does not only fulfill the requirements of electric mobility, but is also found in most portable electric devices. Even though Li-ion batteries are known for their numerous advantages, they undergo serious performance degradation during their aging, and more particularly when used in specific conditions such as at low temperature or high charging current rates. Depending on the operational conditions, different aging mechanisms are favored and can induce physical and chemical modifications of the internal components, leading to performance decay. In this article, the identification of the degradation mechanisms was carried out thanks to an in-depth ante- and post mortem study on three high power and high energy commercial 18,650 cells. Li-ion cells were aged using a battery electric vehicle (BEV) aging profile at −20 °C, 0 °C, 25 °C, and 45 °C in accordance with the international standard IEC 62-660, and in calendar aging mode at 45 °C and SOC 100%. Internal components recovered from fresh and aged cells were investigated through different electrochemical (half-coin cell), chemical (EDX, GD-OES, NMR), and topological (SEM) characterization techniques. The influence of power and energy cells’ internal design and Si content in the negative electrode on cell aging has been highlighted vis-à-vis the capacity and power fade.

The crystal structure, electronic properties, and sodium diffusion mechanism in Na5Sc(MoO4)4 were investigated using the powder X-ray diffraction, nuclear magnetic resonance, and electrical conduct...

We present results of the combined study of the magnetic properties of Li2RuO3 by means of nuclear magnetic resonance (NMR) spectroscopy and theoretical dynamical mean-field theory (LDA + DMFT) calculations. The NMR data clearly show the onset of a thermal activation process in the high temperature region, T > 560K, which is tentatively ascribed to the formation of the valence bond liquid. The LDA + DMFT calculations demonstrate that the magnetic response at these temperatures is mostly due to the xz/yz orbitals, while the xy orbitals of Ru still form molecular orbitals. Thus, Ru ions are in the orbital-selective state in the high temperature phase of Li2RuO3.

The rechargeable Na-ion batteries attract much attention as an alternative to the widely used but expensive Li-ion batteries. The search for materials with high sodium diffusion is important for the development of solid state electrolytes. We present the results of experimental and ab initio studies of the Na-ion diffusion mechanism in Na9Sc(MoO4)6. The ion conductivity reaches the value of 3.6 × 10-2 S cm-1 at T ∼ 850 K. The 23Na and 45Sc NMR data reveal the coexistence of three different types of Na-ion motion in the temperature range from 300 to 750 K. They are activated at different temperatures and are characterized by substantially different dynamics parameters. These features are confirmed by ab initio calculations of activation barriers for sodium diffusion along various paths.

This paper presents the results of lithium dynamics studies of monoclinic β-Li2HfO3. The 6Li MAS and 7Li static NMR experiments and ab initio calculations have been performed to clarify the features of lithium motion in this layered Li-conducting oxide. It was revealed that two types of lithium motion with significantly different characteristic jump frequencies coexist at 425–900 K. One of the processes, responsible for the long-range lithium diffusion, is characterized by an activation energy of Ea = 1.00 ± 0.05 eV and an ion jump frequency of τd–1 ∼ 104 s–1, at T ∼ 750 K. The long-range lithium diffusion represents the successive ion jumps between the nonequivalent octahedral sites in Li/Hf and Li layers, occurring through the distinct type of tetrahedral interstitials (meanwhile, two other types of tetrahedra are less involved in motion). Another type of ion dynamics is the much more rapid localized motion of Li ions with Ea ∼ 0.6 eV and τd–1 ∼ 104 s–1 already at T ∼ 400 K. The mechanisms of lithium mo...

Within the density functional theory the electronic structure of triple molybdates Li2M3Al(MoO4)4, where M = Cs, Rb, is studied for the first time. It is found that all molybdates studied belong to wide band insulators with a band gap of ~4 eV. Quadrupole frequencies and asymmetry parameters of the electric field gradient near magnetic 7Li, 27Al, 87Rb, and 133Cs nuclei are calculated and experimental NMR spectra are interpreted.

Alluaudite-type compounds are currently considered as a promising class of materials for sodium-ion batteries, and understanding of the diffusion processes in them is very important. Using the 23Na MAS NMR and ab initio calculations, we established the mechanism of sodium diffusion in Na4–2xM1+x(MoO4)3 (M ​= ​Mg, Zn, Cd) depending on the type of M-element and x. A comparison of the results obtained for various alluaudite-type compounds shows the crucial effect of the M-cation on the Na-ion dynamics in this class of materials. Higher concentration and charge of M-element increase the concentration of vacancies in the Na-sublattice and enhance the sodium mobility. Moreover, the Na dynamics increases with the M-ion size. The occupancy of the M site and the type of T atom in the TO4 group also determine the mechanism of sodium diffusion in alluaudites, whether it is one-dimensional or two-dimensional. These findings may help a deeper understanding of sodium diffusion processes in alluaudite-type compounds and their development as materials for sodium-ion batteries.

Alluaudite phases are very attractive as both cathode and electrolyte materials for rechargeable sodium-ion batteries. In this work, the combined experimental and DFT studies have been performed to establish the diffusion mechanism in alluaudite-like compound Na5In(MoO4)4. The ionic conductivity was found to reach 3.3 × 10−4 S/сm at 687 K, with an activation energy of 0.66 eV. The sodium diffusion mechanisms have been revealed from the analysis of the 23Na NMR spectra along with the DFT estimations of Na-ion migration barriers. Our results predict that one-dimensional diffusion of sodium in the separate channels along the c-axis is accompanied by the cross-linking jumps providing two-dimensional diffusion in the bc-plane. It is clearly demonstrated that the indium deficiency favors 2D diffusion, but sharply increases the energy barrier for 1D diffusion. Comparison of our results for Na5In(MoO4)4 and related Na5Sc(MoO4)4 shows that the type and deficiency of M-metal in the NaxMy(MoO4)z alluaudites can control the sodium diffusion. The present work highlights the key aspects of cation influence on the diffusion properties in alluaudite materials.

The 1H nuclear magnetic resonance measurements were carried out to study proton dynamics features in the hydrated scandium-doped barium zirconate, BaZr1 − x Sc x O3 − x/2(OH) y , with x = 0.2 and 0.4 in the temperature range 300–600 K. The obtained data evidence a fast proton motion in both samples, which is characterized by the jump frequency of about 108 s−1 at 450 K. However, the microscopic nature of hydrogen diffusion in these two samples is quite different. For the sample with x = 0.2, hydrogen motion mechanisms are defined by a rapid chemical exchange between Sc–OH–Zr and Zr–OH–Zr positions. The estimated value of activation energy for hydrogen diffusion of about 0.5 eV is determined by the energy barrier produced by Sc3+ ion. The increase of Sc concentration to x = 0.4 leads to the drastic changes of sample properties. Experimental results allow to assume the formation of nanoscaled Sc-rich domains and the decomposition of hydrogen sublattice with formation of two proton subsystems: the protons in Zr–OH–Zr coordinations and those concentrated in Sc–OH–Sc environments. The proton motion in both these subsystems is rather fast, but the chemical exchange between them is highly suppressed. Hydrogen motion inside Sc-rich environments has most likely localized nature. Our estimates yield the energy values of about 0.25 and 0.55 eV for hydrogen motion in “free lattice” and in Sc-rich clusters, respectively. The Sc-rich domains can retain hydrogen up to 600 K.

Solid electrolytes are important materials with a wide range of technological applications. This work reports the crystal structure and electrical properties of a new solid electrolyte Na9Al(MoO4)(6). The monoclinic Na9Al(MoO4)(6) consists of isolated polyhedral, [Al(MoO4)(6)](9-) clusters composed of a central AlO6 octahedron sharing vertices with six MoO4 tetrahedra to form a three-dimensional framework. The AlO6 octahedron also shares edges with one NalO(6) octahedron and two Na2O(6) octahedra. Na3-Na5 atoms are located in the framework cavities. The structure is related to that of sodium ion conductor II-Na3Fe2(AsO4)(3). High-temperature conductivity measurements revealed that the conductivity (sigma) of Na9Al(MoO4)(6) at 803 K equals 1.63 X 10(-2) S cm(-1). The temperature behavior of the Na-23 and Al-27 nuclear magnetic resonance spectra and the spin-lattice relaxation rates of the Na-23 nuclei indicate the presence of fast Na+ ion diffusion in the studied compound. At T

The magnetic structure of a quasi-one-dimensional frustrated NaCu2O2 magnet single crystal is studied by NMR. The spatial orientation of the planar spin spirals in the copper-oxygen Cu2+-O chains is determined, and its evolution as a function of the applied magnetic field direction is analyzed.

The 6,7Li NMR spectra and the 7Li spin–lattice relaxation rate were measured on polycrystalline samples of Li2ZrO3, synthesized at 1050 K and 1300 K. The 7Li NMR lines were attributed to corresponding structural positions of lithium Li1 and Li2 by comparing the EFG components with those obtained in the first-principles calculations of the charge density in Li2ZrO3. For both samples the line width of the central 7Li transition and the spin–lattice relaxation time decrease abruptly at the temperature increasing above ~500 K, whereas the EFG parameters are averaged (〈νQ〉=42 (5) kHz) owing to thermally activated diffusion of lithium ions.

The oxygen vacancies distribution in the rigid lattice and the thermally activated motion of oxygen atoms are studied in La{sub 1-x}Sr{sub x}Ga{sub 1-x}Mg{sub x}O{sub 3-x} (x=0.00; 0.05; 0.10; 0.15 and 0.20) compounds. For that {sup 71}Ga, {sup 25}Mg and {sup 17}O NMR was performed from 100 K up to 670 K, and ion conductivity measurements were carried out up to 1273 K. The comparison of the electric field gradients at the Ga- and Mg-sites evidences that oxygen vacancies appear exclusively near gallium cations as a species trapped below room temperature in local clusters, GaO{sub 5/2}-{open_square}-GaO{sub 5/2}. These clusters decay at higher temperature into mobile constituents of the structural octahedra Ga(O{sub 5/6{open_square}1/6}){sub 6/2}. At the same time, the nearest octahedral oxygen environment of magnesium cations persists at different doping levels. The case of two adjacent vacant anion sites is found highly unlikely within the studied doping range. The thermally activated oxygen motion starts to develop above room temperature as is observed from both the motional narrowing of {sup 17}O NMR spectra and the {sup 17}O nuclear spin-lattice relaxation rate. The obtained results show that two types of motion exist, a slow motion and a fast one. The former is a long-rangemore » diffusion whereas the latter is a local back and forth oxygen jumps between two adjacent anion sites. These sites are strongly differentiated by the probability of the vacancy formation, like the vacant apical site and the occupied equatorial site in the orthorhombic compositions x

The NMR spectra of 63Cu and 65Cu natural copper isotopes in a LiCu2O2 multiferroic single crystal compound have been measured above and below the temperature of magnetic phase transition (Tc = 23 K) in zero magnetic field and in applied magnetic field H0 = 94 kOe parallel to the c axis of the crystal. In LiCu2O2 below Tc, a complicated helical magnetic structure with the magnetic moment of copper ions Cu2+ varying along the chain according to the harmonic law with the wave vector being incommensurate to the crystal lattice constants has been revealed. The experimental results have been successfully interpreted using the model based on the planar helical magnetic structure. It has been found that the plane of rotation for Cu2+ magnetic moments in LiCu2O2 does not coincide at H0 = 0 with the ab plane. The high magnetic field (H0 = 94 kOe) applied along the c axis of the single crystal does not affect the spatial orientation of the plane of rotation.

Comprehensive measurements of the 207Pb NMR spectra, Knight shifts 207 K s , spin-lattice relaxation rate 207 T 1 −1 , and the Pb spin echo decay 207 E(2t) in BaPb1 − x Sb x O3 superconducting oxides (x ≤ 0.33) have been performed. A considerable increase in the shift distribution width when Sb is substituted for Pb indicates the formation of the inhomogeneous state of the electron system in the oxide conduction band. The shift magnitude proportional to the density of states near the Fermi energy, 207 K s ∝ N(E F ), reaches its maximum in the compounds with x = 0.18–0.25 with the maximum temperatures T c of the superconducting transition. In the BaPb1 − x Sb x O3 compounds, the Korringa relation is met, indicating that all of the samples are in the metal phase. The data on the Pb spin echo decay and the relevant estimates of the indirect coupling constants of the nuclei of the nearest neighbor Pb atoms clearly demonstrate the development of the electron system state in the oxide metal phase, which is microscopically inhomogeneous over the crystal.

LiTi2(PO4)3 (LTP) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) (S. g. R-3c) have been prepared using conventional ceramic and mechanical activation (MA) methods. It has been shown that preliminary mechanical activation of initial mixtures leads to different nature and amount of dielectric admixtures in the final product after heat treatment at 800–1000 °C as compared with ceramic method. Transport properties of as prepared materials have been studied by lithium ionic conductivity at d.c. and a.c. (complex impedance method), and 7Li NMR spin-lattice relaxation rate T1–1 measurements. Lithium ionic conductivity of mechanochemically prepared LTP and LATP was characterized by significant reduction of grain boundary resistance, especially for LTP, while the bulk conductivity and Li ion diffusion does not noticeably change. The activation energy of bulk conductivity and Li ion diffusion, i.e. short-range motion, appeared to be almost the same for all samples and was equal to ~0.20 eV. On contrary, the activation energy of d.c.-conductivity, i.e. long-range Li ion motion decreases from ~0.6 eV for ceramic samples to ~0.4 eV for samples prepared via mechanochemical route. It was proposed that MA leads to formation of nano-particulate high-conductive grain boundaries both in LTP and LATP.

For the Pu0.95Ga0.05 alloy belonging to the stabilized δ phase of the Pu-Ga system, the 69Ga NMR spectra are measured in the temperature interval 10–650 K and the static magnetic susceptibility χ is measured in the interval T = 20–350 K. In the region T > T* = 235 K, the temperature-dependent magnetic part of the shift K(T) of the Ga NMR line reproduces the χ(T) dependence and follows the Curie-Weiss law K(T) ∼ (T + Θ)−1 with Θ = 280(40) K, which is typical of incoherent spin fluctuations of localized ƒ electrons in concentrated nonmagnetic Kondo systems. The estimate of the effective magnetic moment μeff, 5ƒ (g e = 2) = 0.15(5)μB per Pu atom testifies to a strong suppression of the spin magnetism in the alloy, where the configuration of the ƒ shell of a Pu ion is close to atomic-like ƒ 6. The difference between the K(T) and χ(T) dependences observed for the alloy in the temperature range T < T* is analyzed in terms of the two-fluid description of Kondo lattices developed by Pines et al. [15, 16] in application to the coherent state of a heavy-fermion liquid. Possible causes for the anomalous increase in long-wave contributions in the spatial dispersion of the localized spin susceptibility component of ƒ electrons χƒƒ at temperatures below 50 K are discussed.

The crystal structure and vibrational dynamics of lithium atoms in Li3.75Ge0.75V0.25O4 and Li3.70Ge0.85W0.15O4 solid electrolytes in the superionic state are investigated using neutron diffraction and nuclear magnetic resonance (NMR) spectroscopy. It is found that, in the crystal lattice, lithium ions occupy four nonequivalent positions in the tetrahedral and octahedral oxygen ion environment with vacancies in the octahedra. These findings are in good agreement with the NMR data on the dynamic inhomogeneity of lithium cations in the lattice. It is shown that the origin of the superionic state in the studied compounds is associated primarily with the geometric factor, i.e., with an increase in the size of cavities in the oxygen polyhedra surrounding lithium cations.

International audience; High-resolution solid-state Nuclear Magnetic Resonance (NMR) combined with other investigations was applied to provide essential information on conductive polymer composites based on high-density polyethylene (HDPE) as matrix and multi-walled carbon nanotubes (MWCNTs) or silver nanoparticles (Ag-NPs) as fillers. All composites were prepared by melt mixing using an extrusion process and characterized electrically. By studying the general features of NMR spectra and the molecular dynamic from NMR relaxation parameters, it was possible to obtain structural information about the organization and dispersion of fillers. Due to the paramagnetic or conductive nature of the fillers, it was found that a loss of NMR signal occurred with increasing amounts of filler. In the case of Ag-NPs, this phenomenon was attributed to a skin effect caused by the conductive properties of fillers limiting the adsorption of radiofrequency.

Lithium ionic conductivity and spin-lattice relaxation rates were measured in Li8ZrO6 and Li6Zr2O7 solid electrolytes. It was found that the Li8ZrO6 solid electrolyte undergoes a transition to the superionic state in the temperature range 673–703 K. It was shown that Li+ ions are mobile in particular lattice positions of the Li6Zr2O7 phase, and that ionic conductivity is monotonic at an activation energy of 79.4 kJ/mol.

An $^{17}\text{O}$ NMR study of the distribution of the spin and charge densities of a lightly electron-doped ${\text{CaMnO}}_{3\ensuremath{-}x}$ $(xl0.01,\text{ }{T}_{N}=123\text{ }\text{K})$ ceramic in the paramagnetic phase up to $T=670\text{ }\text{K}$ is reported. The isotropic and anisotropic components of the NMR line shift probe selectively the local spin susceptibility of the itinerant $({e}_{g})$ and the localized $({t}_{2g})$ electrons of the Mn neighbors whereas the nuclear quadrupole parameters look at the distribution of the charge density along the Mn-O bond. When approaching ${T}_{N}$, the spin density of the doped electrons becomes inhomogeneously distributed: a separation into slow carriers, forming magnetic polarons, and fast carriers develops few tens of degrees above ${T}_{N}$. The energy barrier corresponding to the change in carriers mobility was estimated to $\ensuremath{\sim}1100\text{ }\text{K}$. The spin and valence charge densities at the oxygen ions were also measured. From the comparison of these data, the ground state of ${\text{CaMnO}}_{3}$ appears as a charge-transfer insulator state.

7Li NMR spectroscopic experiments on Li2TiO3 demonstrate that the presence of planar crystal defects leads to lithium ion mobility in the temperature range of 30–100°C. Kinetics studies show the number of planar defects (and thus the rate of Li-H ion exchange) depends on the method and conditions of lithium titanate synthesis. The complete exchange of Li+ for H+ results in the formation of crystalline titanium oxyhydroxide TiO(OH)2 due to stabilization of defect state.