Effect Of Lithium Doping Research Articles

UPS Spectra of Lithium‐Doped Carbon Nanostructures: Quantum Chemical Simulations

We present a quantum chemical study on the effect of lithium doping in hydrogen rich carbon nanostructures. To model the hydrogen rich carbon nanostructure we selected hexa‐peri‐hexabenzocoronene, a well‐known polycyclic aromatic hydrocarbon whose UPS spectra have been recorded recently. This study shows that lithium interacts strongly with the carbon nanostructure and does not simply transfer charge to the PAH. As a result, the unusual features observed in the UPS spectra of lithium‐doped HBC are correctly reproduced by the calculations.

Effect of lithium doping on the evolution of rheological and structural properties during gelation of siloxane–poly(oxypropylene) nanocomposites

The influence of lithium doping on the evolution of viscoelastic properties and structure during the gelation of siloxane–poly(oxypropylene) (PPO) nanocomposites has been studied. For several [O]/[Li] ratios (O being the oxygen of the ether-type), dynamic rheological measurements allowed us to follow the evolution of storage and loss moduli, complex viscosity and phase angle during gelation of Li+-doped hybrid sols. All samples exhibit a Newtonian viscous character in the initial step of the process and are progressively transformed into viscoelastic gels. The evolution of the rheological properties of these systems allowed us to determine the aggregation mechanisms of silicon species present in hybrid sols, which lead to sol–gel transformation: mass fractal growth and nearly linear growth at the beginning of gelation, and percolation at the final stage of the process. The influence of doping on the aggregation mechanisms depends on the polymer molecular weight: while for hybrids containing long polymer chains (Mw = 4000 g mol−1) gelation occurs in the initial stages through diffusion-limited monomer–cluster aggregation (DLMCA) for all doping levels, this mechanism is only observed for hybrids containing short chains (Mw = 130 g mol−1) at low lithium concentration ([O]/[Li] = 80). For undoped and high doped siloxane–PPO130 composites ([O]/[Li] = 4), cluster–cluster aggregation is the predominant mechanism occurring at the initial gelation stages. The nature and the proportion of the different coordination sites for lithium cations in the hybrid sols, determined by 7Li NMR and infrared spectroscopy, affect the aggregation mechanisms during gelation and the condensation degree of the siloxane phase in the final dried materials.

Effect of lithium doping on the properties of Tl-basedsuperconductors

The effects of lithium doping on the formation and properties ofthe Tl-based superconductors have been studied. Lithium atoms up to around3 mol.% have been added to the oxides of nominal compositionTl1.8Ba2Ca2.2Cu3Ox, and the usual solid-state reactionmethod has been applied. Lithium additions in the range 0.23-0.29 mol.%increase the fraction of the Tl-2223 phase and significantly improve thecritical temperature of the samples. Higher amounts of lithium additionsdiminish the Tl-2223 phase, reduce the fraction of the Tl-2212 phase, andcause separate non-superconducting phases to be formed.

固相法により作製したＬｉ添加Ｂｉ‐２２１２相への電気化学的手法によるＬｉのインターカレーション

The effects of lithium doping by solid state reaction on the electrochemical intercalation into the Bi-2212 phase with lihium were investigated through the structure and superconducting properties. The expansion rates of lattice parameters with respect to the amount of lithium intercalated by electrochemical reaction decreased with increasing the amount of lithium doped by solid state reaction. The change of superconducting critical temperature with respect to average valence of copper became small with increasing the amount of lithium doped by solid state reaction. The electrochemical reaction removed lithium from Bi-2212 phase as much as the amount of lithium intercalated by electrochemical reaction. The result supports the possibility that lithium doped by solid state reaction and electrochemical reaction occupies the different sites in the Bi-2212 phase.

Effect of Lithium Doping in the Bi‐2212 Superconducting System

AbstractSamples with the nominal composition Bi2Sr2Ca1–xLixCu2Oy (x = 0.2,0.4, and 0.6) and Bi2Sr2CaCu2−x L1xOz (x = 0.4, 0.6, and 1.0) were prepared by the solid state reaction method. The role of L1 at both Ca and Cu sites in the Bi‐2212 composition were studied. From the X‐ray diffraction data it was found that the L1‐doped at the Ca site increases the c‐axis and that doped at the Cu site decreases the c‐axis. From the D.C. four‐probe resistivity data it was found that Li‐doped at the Ca site reduces the Tc and the L1‐doped at the Cu site gives Tc(0) above the liquid nitrogen temperature. It was observed that the L1 doping reduces the melting point of Bi‐2212 composition. The presence of Lithium was confirmed by inductive the coupled plasma method.

Effect of lithium doping on the conductivity of poly( p-phenylene vinylene)

The effect of lithium doping on the conductivity (σ) of poly( p-phenylene vinylene) (ppv) has been studied via a.c. impedance measurements. Ppv has been synthesized via a water-soluble polymer electrolyte precursor. Its conductivity in both undoped and doped forms has been measured as a function of temperature. While doping with LiCl has not resulted in reliable data, doping with lithium triflate (LiCF 3SO 3) has improved the conductivity of ppv by more than two orders of magnitude. Plots of log(σ) versus 1/ T show that the conductivities of undoped and doped ppv follow Arrhenius behavior with equal activation energies ( E a ≈ 0.37 eV). The increase in conductivity without a change in activation energy is attributed to the increase in the electronic density of ppv.

Effects of γ irradiation and lithium doping on the catalytic activity of nickel-aluminum mixed oxides

The catalytic activity of pure NiO and Ni-Al mixed oxides subjected to various doses of γ irradiation was investigated using the oxidation of CO with O 2 at various temperatures. The effect of lithium doping on the catalytic activity of Ni-Al was also investigated. The results obtained revealed that γ irradiation of pure NiO using doses up to 10 Mrad effected a decrease of 45% in its catalytic activity which suffered a further slight change when the dose was increased to 20 Mrad. The activity of Ni-Al mixed oxide was modified in a somewhat complicated manner by γ irradiation. Doses of 5 – 10 Mrad produced an increase of 34% in its catalytic activity and a dose of 15 Mrad caused a drastic decrease in its activity of 57%. Increasing the dose of 20 Mrad produced a slight increase in the catalytic activity of the mixed oxide solid. The modifications in the catalytic activity of pure NiO and mixed oxide solids arising from γ irradiation were attributed to an induced removal of chemisorbed O 2 in the case of pure NiO and to a possible increase in the [Ni]/[Al] ratio, especially in the outermost surface layers, of the mixed oxide catalyst. Lithium doping was found to cause a significant increase in the catalytic activity of Ni-Al mixed oxide which was attributed to the increase in the amount of chemisorbed O 2 and to an increase in the [Ni]/[Al] ratio.

Moderate and high temperature doping of cobaltic oxide catalyst with lithium oxide

Pure and lithium-doped cobaltic oxide (Co 3O 4) samples were prepared by thermal decomposition of pure basic cobalt carbonate and of mixtures of Co 3O 4 with different proportions of lithium hydroxide. The thermal dissociation of pure and doped solids was carried out in air at temperatures in the range 500–1100 °C. The effects of lithium doping on the surface area of Co 3O 4 and on its catalytic activity in CO oxidation at 125–220 °C were investigated. The influence of doping on the thermal reduction of Co 3O 4 to CoO was also studied using X-ray diffraction and differential thermal analysis (DTA) techniques. Incorporation of lithium ions into the Co 3O 4 lattice at temperatures equal to or greater than 700 °C decreased drastically its catalytic activity and its specific surface area. By contrast, doping at 500 °C, although it increased substantially the surface area of the doped oxide, decreased its catalytic activity. X-ray diffraction showed that the thermal treatment of pure basic cobalt carbonate in air at 500–700 °C effected its complete conversion into Co 3O 4 which underwent a partial reduction at 900 °C yielding CoO. At 1100 °C, Co 3O 4 decomposed entirely, producing cobaltous oxide. The presence of lithium ions in Co 3O 4 (3%–6% Li + (mol Co 3O 4 -1) effectively retarded its reduction into CoO from 900 to 1050 °C. A prolonged heating of doped oxide at 1100 °C affected only its partial decomposition into CoO. The retardation of cobaltous oxide formation was also confirmed by DTA. The incorporation of lithium ions into Co 3O 4 stabilized its lattice against the thermal reduction to the cobaltous oxide phase. New diffraction lines appeared in all doped oxide samples heated in air at 900–1100 °C. These lines may be due to the formation of a new lithium oxide-cobalt oxide compound. The possible mechanisms of lithium doping are discussed.

Effects of lithium doping on textural characteristics of Co3O4 catalyst

The effects of lithium content (0.75%, 3% and 6% Li+) and calcination temperature (400, 500, 600 and 700 °C) on different surface properties of Co3O4 were investigated. The various texture parameters of pure and doped oxide samples were computed from data on nitrogen adsorption at 77 K.The dissolution of monovalent lithium ions in the Co3O4 lattice at temperatures equal to or greater than 700 °C was accompanied by a marked decrease in the surface area, total pore volume and most probable pore radius of the catalyst. In contrast, doping in the temperature range 400 – 600 °C led to a marked increase in the specific surface area of Co3O4; this attained a maximum value at 500 °C (a 94% increase). The most probable pore radius increases for the oxide doped with 0.75% Li then decreases with increasing amount of dopant ions. The total pore volumes of all doped oxide samples are smaller than those measured for pure oxide specimens.The possible mechanisms of doping of Co3O4 with lithium ions are discussed.

Effects of lithium doping on the catalytic activity of Co 3O 4 in CO oxidation

The catalytic oxidation of CO on the surface of pure and lithium-doped Co 3O 4 catalysts was carried out by a static method at various temperatures between 95 and 250 °C in an atmosphere containing 2 parts CO to 1 part oxygen at a pressure of 2 Torr. The catalyst samples were prepared by the thermal decomposition of pure basic cobalt carbonate and of cobalt carbonate mixed with different proportions of LiOH (0.75, 3 and 6 at.%) in air at 500 and 700 °C. All the doped catalysts exhibited lower activities than those of the pure oxides at all the reaction temperatures. The decrease in the catalytic activity was most pronounced for the doped catalysts prepared at 700 °C. Although doping at 500 °C was accompanied by a significant increase in the catalyst surface area, the catalytic activity of the sample was decreased. The apparent activation energy E of CO oxidation on pure Co 3O 4 prepared at 500 °C was 6.7 kcal mol −1 in the temperature range 95–150 °C. This value increased to 22.1 kcal mol −1 in the temperature range 110–145 °C on addition of 3 at.% Li to the pure catalyst. The value of E for pure Co 3O 4 prepared at 700 °C was 2.0 kcal mol −1 in the temperature range 150–220 °C which increased to 14.9 kcal mol −1 in the temperature range 200–250 °C on addition of 3 at.% Li.