Radial Functions of Diatomic Lithium Halides X 1Σ+ From Vibration-Rotational Spectra

The radial functions for potential energy and adiabatic and nonadiabatic effects in the forms of polynomials with coefficients c_j, h_j ^Li, h_j ^X, g_j ^Li and g_j ^X of the reduced variable for internuclear distance z=2.(R-R_e)/(R+R_e) to various non-negative powers have been determined for the family of diatomic molecules of the lithium halides, LiF, LiCl, LiBr and LiI, with the corresponding results of LiH included for purposes of comparison. Trends are evident in the coefficients of lower order, but those of higher order are susceptible not only to the influence of the extent and quality of the data but also to the truncation of the power series in the representations. The various radial functions are valid with the specified ranges of internuclear distance depending on the maximum extent of vibrational excitation of the spectra.     

Intercalation of lithium ions into bulk and powder highly oriented pyrolytic graphite

The electrochemical reactions of highly oriented pyrolytic graphite (HOPG) bulk and powder electrodes in 1 M LiPF₆ 1:1 EC/DMC solution were investigated and the results show that the intercalation reaction of lithium ion into HOPG electrode occurs only at the edge plane and SEI formation reaction on the basal plane is negligible in comparison with that on the edge plane. The active surface area of HOPG powder electrode could be deduced by comparing the peak area (consumed charge for SEI formation) at potential of 0.5 V on voltammograms with that of bulk HOPG edge electrode. The diffusion coefficients of lithium ion in HOPG bulk layers and in HOPG powder was for the first time measured by use of electrochemical impedance spectra and potential step chronamperameter methods. It was found that the diffusion coefficients of lithium in HOPG were in the range of 10⁻¹¹-10⁻¹² cm² s⁻¹ for the lithium-HOPG intercalation compounds at potentials from 0.2 (vs. Li/Li⁺) to 0.02 V, decreasing with the increase of lithium intercalation degree. A good agreement was obtained between the results from bulk and powder HOPG electrodes by electrochemical impedance spectra method.     

Synthesis and characterization of lithium ferrite by oxalate precursor route

Nanocrystalline lithium ferrite (LiFe₅O₈) powders have been synthesized by oxalate precursor route. The effects of Fe³⁺/Li⁺ mole ratio, and annealing temperature on the formation, crystalline size, morphology and magnetic properties were systematically studied. The Fe³⁺/Li⁺ mole ratio was controlled from 5 to 3.33 while the annealing temperature was controlled from 600 to 1100 °C. The resultant powders were investigated by differential thermal analyzer (DTA), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). DTA results showed that LiFe₅O₈ phase started to form at around 520 °C. XRD indicated that LiFe₅O₈ phase always contained α-Fe₂O₃ impurity and the hematite phase formation increased by increasing the annealing temperature ?850 °C for different Fe³⁺/Li⁺ mole ratios 5, 4.55 and 3.85. Moreover, lithium ferrite phase was formed with high conversion percentage at critical annealing temperature 750–800 °C. Single well crystalline LiFe₅O₈ phase was obtained at Fe³⁺/Li⁺ mole ratio 3.33 and annealing temperatures from 800 to 1000 °C. Maximum saturation magnetization (68.7 emu/g) was achieved for the formed lithium ferrite phase at Fe³⁺/Li⁺ mole ratio 3.33 and annealing temperature 1000 °C.     

Ab initio electronic, dynamic, and thermodynamic properties of isotopic lithium hydrides (LiH, LiD, LiT, LiH, LiD, and LiT)

The structural, dielectric, lattice-dynamical, and thermodynamical properties of isotopic lithium hydrides (⁶LiH, ⁶LiD, ⁶LiT, ⁷LiH, ⁷LiD, and ⁷LiT) were investigated within density-functional theory. The atomic structure was fully relaxed and the structural parameters were found to differ by less than 2% from the experimental data. The associated electronic band structure and density of states were also presented. A linear-response approach to the density-functional perturbation theory was employed to work out the Born effective charges, dielectric tensors and phonon frequencies, and thermodynamic properties. The compounds with the heavier Li isotope or H isotope have the lower phonon frequencies; ⁶LiT is more stable than ⁷LiT, ⁶LiD, ⁷LiD, ⁶LiH, and ⁷LiH in the temperature range 0-2700 K. These properties of LiT were predicted for the first time. The results were discussed in terms of the isotope effects on phonon dispersion curves and thermodynamic properties.     

Diffusion of Li ion in graphite cluster model at 800 K: a direct molecular orbital dynamics study

Using the hydrogen terminated planar cluster model, C₅₄H₁₈, the stabilization site of Li⁺ ion was determined by the unrestricted Hartree-Fock (UHF) AM1 energy gradient method. Six kinds of stabilization sites are considered, suggesting that the Li⁺ ion is rather stable at the two distinct sites in the bulk where the potential energy difference between them is 2.0 kcal/mol. For the Li⁺ ions stabilized at these two sites, the diffusion processes were simulated at 800 K through the direct molecular orbital dynamics procedure which was newly developed by one of the present authors. No jumping diffusion occurs with Li⁺ ions among the stabilization sites, but they diffuse along the outline of the cluster model with the fluctuations. It takes 2.0 ps for a Li⁺ ion to diffuse from the lower potential site to another equivalent site. On the other hand, it takes 0.7 ps to move from the higher potential site to the unstable circumference site composed of corner (armchair edge) carbon atoms. As the result, the diffusivity is approximated as 10⁻⁸-10⁻⁷ m²/s.     

Ceramics for fusion reactors: The role of the lithium orthosilicate as breeder

Lithium-based oxide ceramics are studied as breeder blanket materials for the controlled thermonuclear reactors (CTR). Lithium orthosilicate (Li₄SiO₄) is one of the most promising candidates because of its lithium concentration (0.54 g/cm³), its high melting temperature (1523 K) and its excellent tritium release behavior. It is reported that the diffusion of tritium is closely related to that of lithium, so it is possible to find an indirect measure of the trend of tritium studying the diffusivity of Li⁺.     

Defect clusters in titanium-substituted spinel-related lithium ferrite

The cation distribution in spinel-related titanium-substituted lithium ferrite, Li_0.5+0.5xFe_2.5−1.5xTi_xO₄ has been explored using interatomic potential and ab initio calculations. The results suggest that the cation distribution with Ti⁴⁺ substituting for Fe³⁺ on octahedral B sites and excess Li⁺ substituting for Fe³⁺ on tetrahedral A sites is stabilised by the formation of clusters of two octahedrally coordinated Ti⁴⁺ ions and one tetrahedrally coordinated Li⁺ ion linked through a common oxygen.     

Preparation and electrical properties of the 0,37Li2S-0,18P2S5-0,45LiI glass

A new lithium vitreous electrolyte has been found in the LiI---Li₂S---P₂S₅ system. LiI concentration in the glass, 45% moles, is close to the solubility limit of LiI in 2Li₂S---P₂S₅ glass.The activation energy is of the order of 7.2 Kcal.mole⁻¹ and the conductivity value is 10⁻³ (ohm cm)⁻¹ at 25°C. The conduction is ionic and assured by Li⁺ ions.     

Desorption of chemisorbed Carbon on Mo(1 0 0) by noble gas ion sputtering: Validation of ground test measurements of ion engine lifetimes

We report desorption cross section measurements for one monolayer of chemisorbed carbon on a Mo(1 0 0) surface induced by sputtering with noble gas ions (Ne⁺, Ar⁺, Xe⁺) at different incident angles, ion energies, and substrate temperatures. Desorption cross sections were determined by using low-energy ion scattering (LEIS) to monitor the increase of the signal from the Mo substrate. A monolayer of p(1 × 1) carbon adatoms on the Mo(1 0 0) surface was created by dosing ethylene (C₂H₄) to the substrate at 800 K, and characterized by Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). We find that the carbon desorption cross section increases with increasing mass and energy of the impinging ions, and there is a maximum value for the desorption cross section at an incident angle for the ions of 30° from the surface plane. The desorption cross section also increases up to a substrate temperature of 300 °C. Values for the carbon desorption cross section for carbon adatoms on Mo(1 0 0) by 400-eV Xe⁺ ion sputtering are about 2 × 10⁻¹⁵ cm², which is one order of magnitude higher than those for bulk carbon samples. This information is particularly important for evaluation of ion-engine lifetimes from ground-test measurements in which contaminant carbon is deposited on Mo accelerator grids, potentially altering the sputtering rate of the Mo. Our measurements show that monolayer amounts of carbon on Mo have desorption cross sections that are two orders of magnitude higher than estimates of what would be required to reduce the Mo erosion rate, and thus ground-test measurements can be used with confidence to predict ion-engine wear in space, from this perspective.     

Electrochemical properties of electrosynthesized TiO2 thin films

Titanium dioxide (TiO₂) thin films prepared by cathodic electrodeposition on indium-tin-oxide coated glass substrates from simple aqueous peroxo-titanium complex solutions have been studied as a function of sintering temperature (25-500 °C). The films crystallized in to anatase phase at relatively low temperature (300 °C). Electrochemical properties of amorphous and anatase films were investigated by cyclic voltammogram (CV) in lithium ion containing organic electrolyte. All the films were found to show reversible electrochemical properties upon Li⁺ ion intercalation. The effects of sintering temperature on the crystallinity and consequently on the electrochemical properties of TiO₂ has been discussed.     

Mechanism and kinetics of lithium vapor capture in a high-temperature packed bed of kaolinite

This study investigated the characteristics of high-temperature lithium vapor-capturing reaction in a packed bed of calcined kaolin particles. The packed-bed sorption experiments were carried in the a temperature range of 700-900 °C. The high-temperature reaction between LiCl vapor and calcined kaolin sorbent generated lithium aluminum silicate (Li₂O·Al₂O₃·2SiO₂). An increase in kaolin bed temperature results in an increase in lithium-capturing rate, but it has no effect on the maximum lithium uptake. The resistance of LiCl vapor diffusion into the pores of calcined kaolin particles was negligible, and the chemical reaction at the kaolin surface controlled the overall sorption reaction rates by up to 60% of metakaolinite conversion. The order of the reaction between metakaolinite and LiCl vapor was determined as 1.94 and its activation energy was estimated as 7.95 kcal/mol according to the Arrhenius relationship.     

Study of lithium adsorption on the TiO2 surface by electron-stimulated desorption

This paper reports on a study of electron-stimulated desorption (ESD) of O⁺ and Li⁺ ions from titanium dioxide as a function of the preheating temperature T and of the concentration of lithium adsorbed at 300 K, which was carried out with a static magnetic mass spectrometer combined with a retarding-field energy analyzer. For T>1500 K, the TiO₂ surface undergoes irreversible rearrangement. At temperatures from 300 to 900 K and at lithium coverages Θ<1, the ESD cross sections of the O⁺ and Li⁺ ions vary in a reversible manner with temperature, while for lithium coverages Θ>1, the changes in the Li⁺ and O⁺ ESD cross sections become irreversible. For θ<1, the appearance threshold of the Li⁺ and O⁺ ions is 25 eV, whereas for θ>1, the ESD threshold of Li⁺ ions shifts to 37 eV.     

Nitration of phenols in reversed micelle systems and enhanced oxidation ability of dilute nitric acid (less than 2.0 molarity) in concentrated salt solutions

In a previous paper, we have reported that dilute nitric acid in reversed micelle systems can oxidize the Br⁻ ion to Br₂ and proposed that the nitryl (or nitronium) ion NO₂⁺ should be the active species in the oxidation process. Nitration of phenol in reversed micelle systems with dilute nitric acid, CHCl₃/CTAC/H₂O (2.0 mol dm^− 3 HNO₃ in the 1.0% (v/v) H₂O phase), was performed at 35 °C to obtain 2- and 4-nitrophenols, where CTAC represents cetyltrimethylammonium chloride. In similar CTAC and AOT reversed micelle (CHCl₃ or heptane/AOT) systems, 4-methylphenol was converted to 2-nitro-4-methylphenol, where AOT stands for sodium bis(2-ethylhexyl) sulfosuccinate. In aqueous 2.0 mol dm^− 3 HNO₃ solution accompanied by 4.0 mol dm^− 3 LiCl (and a small amount of LiBr as the bromide resource), trans-1,4-dibromo-2-butene was successfully brominated to 1,2,3,4-tetrabromobutane. This result is a good evidence that the Br⁻ ion can be oxidized to Br₂ in dilute nitric acid (2.0 mol dm^− 3) provided that it contains concentrated salts. At 20-40 °C, the apparent oxidation-reaction rate constants (k/s^− 1) of Br⁻ to Br₂ were evaluated in 0.1-2.0 mol dm^− 3 HNO₃ solution accompanied by concentrated LiCl (3.5-9.0 mol dm^− 3). For chloride salts, the cation effects increased as Et₄N⁺ ? Na⁺ < Li⁺ < Ca²⁺ < Mg²⁺. Even the evolution of Cl₂ was demonstrated from < 2.0 mol dm^− 3 HNO₃ solution containing concentrated LiCl, MgCl₂, and CaCl₂ as well as AlCl₃, therefore, an indirect oxidation mechanism of the Br⁻ ion through Cl₂ was proposed as follows: 2Cl⁻ + NO₂⁺ → Cl₂ + NO₂⁻; 2Br⁻ + Cl₂ → Br₂ + 2Cl⁻.     

Structural characterization for the chemically Li ion extracted LiyCoO2, LiyCo0.95Ga0.05O2, and LiyCo0.9Ga0.1O2 compounds

Chemical Li ion extraction processes have been carried out for pristine LiCoO₂, LiCo_0.95Ga_0.05O₂, and LiCo_0.9Ga_0.1O₂ compounds by swirling them in 0.35 M H₂SO₄ solution. It is confirmed from XRD patterns that the compounds maintain the two-dimensional framework with pristine-type structure even after the acid treatment up to 12 h. The Ga-substituted compounds keep Li ions for longer time on the acid treatment rather than the LiCoO₂. The average oxidation state of Co ions increases with the Li⁺ ion extraction time up to 3.45+. The local structure refinements for the chemically Li⁺ ion extracted compounds have been investigated by Co K-edge X-ray absorption spectroscopy. The extraction causes the increase of Debye-Waller (DW) factor or static disorder around the Co ion. The DW factor of the Co-Co bond pair less increases with the extraction time for the Li_yCo_0.95Ga_0.05O₂, and Li_yCo_0.9Ga_0.1O₂ compounds than that for the LiCoO₂. The Ga-substituted compounds are more stable against acid treatments than the LiCoO₂, since more basic Ga³⁺ ion retards the structural distortion of the CoO₆ octahedra against the Li ion extraction.     

Electron paramagnetic resonance and thermoluminescence study of Ag ions in Li2B4O7 crystals

Electron paramagnetic resonance (EPR) is used to investigate the effects of ionizing radiation on Ag-doped lithium tetraborate (Li₂B₄O₇) crystals. Two similar, yet distinct, trapped-hole centers (Ag²⁺ ions substituting for Li⁺ ions) are produced by 60 kV x rays. One Ag²⁺ ion, labeled Center A, has no nearby defects and the other Ag²⁺ ion, labeled Center B, has a neighboring impurity which is most likely a Ag⁺ ion substituting for a Li⁺ ion. The production and thermal decay properties of the two Ag²⁺ ions are described and their g matrices and ¹⁰⁷Ag and ¹⁰⁹Ag hyperfine matrices are obtained from the EPR angular dependences. The principal values of the g matrices are similar for the two centers, but the hyperfine principal values differ significantly (Center B has smaller values than Center A). There are also differences in the directions of the principal axes for the two centers. Together, these results imply (1) that the unpaired spin is less localized for Center B and (2) that the ground-state positions of the neighboring oxygen ions are different for Centers A and B. This explains why the peaks of the Ag²⁺ charge-transfer photoluminescence bands associated with Centers A and B occur at different wavelengths (502 and 725 nm, respectively). An isochronal pulsed thermal anneal shows that these radiation-induced Ag²⁺ ions serve as the recombination site for the intense thermoluminescence peak observed near 152 °C.     

Electron stimulated desorption of H3O from 316L stainless steel

Surface ions generated by electron stimulated desorption from mass spectrometer ion source grids are frequently observed, but often misidentified. For example, in the case of mass 19, the source is often assumed to be surface fluorine, but since the metal oxide on grid surfaces has been shown to form water and hydroxides, a more compelling case can be made for the formation of hydronium. Further, fluorine is strongly electronegative, so it is rarely generated as a positive ion. A commonly used metal for ion source grids is 316L stainless steel. Thermal vacuum processing by bakeout or radiation heating from the filament typically alters the surface composition to predominantly Cr₂O₃. X-ray photoelectron spectral shoulders on the O 1s and Cr 2p_3/2 peaks can be attributed to adsorbed water and hydroxides, the intensity of which can be substantially increased by hydrogen dosing. On the other hand, the sub-peak intensities are substantially reduced by heating and/or by electron bombardment. Electron bombardment diode measurements show an initial work function increase corresponding to predominant hydrogen desorption (H₂) and a subsequent work function decrease corresponding to predominant oxygen desorption (CO). The fraction of hydroxide concentration on the surface was determined from X-ray photoelectron spectroscopy and from the deconvolution of temperature desorption spectra. Electron stimulated desorption yields from the surface show unambiguous H₃O⁺ peaks that can be significantly increased by hydrogen dosing. Time of flight secondary ion mass spectrometry sputter yields show small signals of H₃O⁺, as well as its constituents (H⁺, O⁺ and OH⁺) and a small amount of fluorine as F⁻, but no F⁺ or F⁺ complexes (HF⁺, etc.). An electron stimulated desorption cross-section of σ⁺ ∼ 1.4 × 10⁻²⁰ cm² was determined for H₃O⁺ from 316L stainless steel for hydrogen residing in surface chromium hydroxide.     

Room temperature lithium fast-ion conduction and phase relationship of LiI stabilized LiBH4

In the present work, we focus attention on the effect of LiI addition to newly discovered pure lithium ion conductor, LiBH₄. Solid solution of the composition LiBH₄-LiI (LiI: 6.25-33.3 mol%) was synthesized by solid state reaction. Electrical conductivity was measured from room temperature to 140 °C by ac impedance method, which revealed the fast-ion conduction phase of LiBH₄ can be stabilized to lower temperature, below the room temperature. Solid solution with LiI showed higher conductivities and lower activation energies in comparison with LiBH₄. Powder XRD measurement was carried out at 120 °C (just above the transition temperature of LiBH₄). The lattice constants of the solid solution were determined. DSC measurement showed a systematic compositional dependence on the transition temperature. The stabilization mechanism was discussed.     

Characterization of solid electrolytes prepared from ionic glass and ionic liquid for all-solid-state lithium batteries

Glassy solid electrolytes were prepared by combining the 50Li₂SO₄·50Li₃BO₃ (mol%) ionic glass and the 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMI]BF₄) ionic liquid. High-energy ball milling was carried out for the mixture of the inorganic ionic glass and the organic ionic liquid. The ambient temperature conductivity of the glass electrolyte with 10 mol% [EMI]BF₄ was 10⁻⁴ S cm⁻¹, which was three orders of magnitude higher than that of the 50Li₂SO₄·50Li₃BO₃ glass. The addition of [EMI]BF₄ to the ionic glass decreased glass transition temperature (T_g) of the glass and the decrease of T_g is closely related to the enhancement of conductivity of the glass. Morphology and local structure of the glass electrolyte was characterized. The dissolution of an ionic liquid in an ionic glass with Li⁺ ion conductivity is a novel way to developing glass electrolytes for all-solid-state lithium secondary batteries.     

Modeling and simulation of Li-ion conduction in poly(ethylene oxide)

Polyethylene oxide (PEO) containing a lithium salt (e.g., LiI) serves as a solid polymer electrolyte (SPE) in thin-film batteries and its ionic conductivity is a key parameter of their performance. We model and simulate Li⁺ ion conduction in a single PEO molecule. Our simplified stochastic model of ionic motion is based on an analogy between protein channels of biological membranes that conduct Na⁺, K⁺, and other ions, and the PEO helical chain that conducts Li⁺ ions. In contrast with protein channels and salt solutions, the PEO is both the channel and the solvent for the lithium salt (e.g., LiI). The mobile ions are treated as charged spherical Brownian particles. We simulate Smoluchowski dynamics in channels with a radius of ca. 0.1 nm and study the effect of stretching and temperature on ion conductivity. We assume that each helix (molecule) forms a random angle with the axis between these electrodes and the polymeric film is composed of many uniformly distributed oriented boxes that include molecules with the same direction. We further assume that mechanical stretching aligns the molecular structures in each box along the axis of stretching (intra-box alignment). Our model thus predicts the PEO conductivity as a function of the stretching, the salt concentration and the temperature. The computed enhancement of the ionic conductivity in the stretch direction is in good agreement with experimental results. The simulation results are also in qualitative agreement with recent theoretical and experimental results.     

Structural studies and ionic conductivity of lithium iodide-lithium tungstate solid electrolytes

Solid mixtures of calcined lithium iodide - lithium tungstate (LiI -Li₂WO₄) have been found to be potential solid electrolytes for practical applications with high conductivities of about 10⁻³ S·cm⁻¹ at room temperature. The highest ionic conductivity was recorded for the sample containing 20 wt.-% of lithium iodide. The ionic conductivity was related to the structure of the material using X-ray diffraction (XRD) and infrared techniques (FTIR). These experiments confirm the evidence of interaction between LiI and Li₂WO₄. FTIR spectroscopy revealed the existence of a band at 1505 cm⁻¹ which is formed as a result of this LiI -Li₂WO₄ interaction. The new phase acts as a conducting pathway for the ions to migrate through the material. Lithium ionic conduction was confirmed by measuring the transference number by Wagner's polarization technique. The ionic transference number of this solid electrolyte was found to be 1 within the limits of error.