Lithium Doping Research Articles

Defect Control in a Selective Reduction Reaction to Synthesize a Metal/Ceramic Nanocomposite

A metal/ceramic nanocomposite was synthesized by defect control in a selective reduction reaction of a complex solid solution. The defect type of a (Co, Mg)O solid solution was controlled by doping oxides with different valencies. The controlled defects strongly affected the reduction reaction behaviors as well as material morphologies after the reaction. In the case of scandium doping, the diffusion was rate controlling in the reduction reaction, and metals of a nanocolumn-like structure were highly dispersed into the matrix. On the other hand, in the case of lithium doping, the interface reaction was rate controlling in the reaction, and metal nanoparticles were highly dispersed into the matrix.

Li-DOPING EFFECT ON THE CATHODOLUMINESCENT PROPERTIES OF Y2O3:Eu3+ PHOSPHORS

Influence of lithium doping on the crystallization, the surface morphology, the chemical states and the luminescent properties of Y 2 O 3: Eu 3+ phosphors was investigated. The structural, surface morphology characteristics and chemical states of the phosphors were analyzed by using X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS), respectively. The crystallinity, the surface morphology, and the cathodoluminescence (CL) of phosphors highly depended on the Li doping. The relationship between the crystalline and morphological structures and the luminescent properties was studied, and Li + doping affected not only the crystallinity but also the luminescent brightness of Y 2 O 3: Eu 3+ phosphors. In particular, the incorporation of the Li + ion into the Y 2 O 3 lattice could induce remarkable increase in the CL intensity. The enhanced photoluminescence brightness with Li doping may result both from the improved crystallinity leading to higher oscillating strengths for the optical transitions, and the increased surface area due to the larger particle sizes. The strongest emission intensity was observed with Li doped Y 2 O 3: Eu 3+ ceramics whose brightness was increased by a factor of 1.8 in comparison with that of Y 2 O 3: Eu 3+ ceramics.

Thermal properties of Li 4/3Ti 5/3O 4/LiMn 2O 4 cell

The thermal properties of Li 4/3Ti 5/3O 4 and Li 1+ x Mn 2O 4 electrodes were investigated by isothermal micro-calorimetry (IMC). The 150-mAh g −1 capacity of a Li/Li 4/3Ti 5/3O 4 half cell was obtained through the voltage plateau that occurs at 1.55 V during the phase transition from spinel to rock salt. Extra capacity below 1.0 V was attributed to the generation of a new phase. The small and constant entropy change of Li 4/3Ti 5/3O 4 during the spinel/rock-salt phase transition indicated its good thermal stability. Accelerated rate calorimetry confirmed that Li 4/3Ti 5/3O 4 has better thermal characteristics than graphite. The IMC results for a Li/Li 1+ x Mn 2O 4 half cell indicated less heat variation due to the suppression of the order/disorder change by lithium doping. The heat profiles of the Li 4/3Ti 5/3O 4/Li 1+ x Mn 2O 4 full cell indicated less heat generation compared with a mesocarbon-microbead graphite/Li 1+ x Mn 2O 4 cell.

Oxidative Coupling of Methane over Lithium Doped (Mn+W)/SiO 2 Catalysts

Abstract Modification and performance of Li induced silica phase transition of (Mn+W)/SiO 2 catalyst, under reaction conditions of oxidative coupling of methane (OCM), have been investigated employing textural characterizations and redox studies. Stability and precrystalline form of fresh Li induced silica phase transition catalyst depend on the Li loading. A catalyst, with high lithium loading, destabilizes on OCM stream. This destabilization is not due to Li evaporation at OCM reaction conditions, a-cristobalite is proposed to be an intermediate in the crystallization of amorphous silica into quartz in the Li-induced silica phase transition process. However, the type of crystalline structure was found to be unimportant with regard to the formation of a selective catalyst. Metal-metal interactions of Li-Mn, Li-W and Mn-W, which are affected during silica phase crystallization, are found to be critical parameters of the trimetallic catalyst and were studied by TPR. Role of lithium in Li doped (Mn+W)/SiO 2 catalyst is described as a moderator of the Mn-W interaction by involving W in silica phase transition. These interactions help in the improvement of transition metal redox properties, especially that of Mn, in favor of OCM selectivity.

Preparation and lithium doping of gallium oxynitride by ammonia nitridation via a citrate precursor route

Gallium oxynitride, isostructural to hexagonal gallium nitride (h-GaN), was obtained by ammonia nitridation of a precursor prepared from the addition of citric acid to an aqueous solution of gallium nitrate. Gallium oxynitride produced at 750 °C had a small amount of gallium vacancies, and was formulated as (Ga 0.89□ 0.11) (N 0.66O 0.34) where the symbol □ stands for gallium vacancy. Both the gallium vacancies and oxygen substituted for nitrogen were randomly distributed within the structure. The amount of vacancies decreased with nitridation temperatures in the range of 750–850 °C. Approximately, 10 at% Li + was doped into the gallium oxynitride, using a similar preparation with the additional presence of lithium nitrate, resulted in the random substitution of Ga 3+ in an atomic ratio of Li/Ga<1 at 750 °C. Oxygen was codoped with lithium and substituted nitrogen in the wurtzite-type crystal lattice. These substitutions reduced the electrical conductivity in the gallium oxynitride semiconductor. A new oxynitride, Li 2Ga 3NO 4, was also obtained with Li 2CN 2 impurity using similar preparations from a mixture of Li/Ga⩾1. The crystal structure was isostructural with h-GaN, and was refined as P6 3 mc with a=0.31674(1) nm, and c=0.50854(2) nm. The Ga and Li occupancies at the 2 b site were refined to be 0.6085 and 0.3915, respectively, assuming that the other 2 b site was randomly occupied with 1/5O and 4/5N. When the new compound was washed for over 1 min for the removal of Li 2CN 2 impurities, it was decomposed to a mixture of α-GaOOH and α-LiGaO 2. The as-prepared product with Li/Ga=1 showed the highest intensity in yellow luminescence among the products under excitation at 254 nm.

Isothermal calorimetry investigation of Li 1+ xMn 2− yAl zO 4 spinel

The heat generation of LiMn 2O 4, Li 1.156Mn 1.844O 4, and Li 1.06Mn 1.89Al 0.05O 4 spinel cathode materials in a half-cell system was investigated by isothermal micro-calorimetry (IMC). The heat variations of the Li/LiMn 2O 4 cell during charging were attributed to the LiMn 2O 4 phase transition and order/disorder changes. This heat variation was largely suppressed when the stoichiometric spinel was doped with excess lithium or lithium and aluminum. The calculated entropy change (d E/d T) from the IMC confirmed that the order/disorder change of LiMn 2O 4, which occurs in the middle of the charge, was largely suppressed with lithium or lithium and aluminum doping. The d E/d T values obtained did not agree between the charge and the discharge at room temperature (25 °C), which was attributed to cell self-discharge. This discrepancy was not observed at low temperature (10 °C). Differential scanning calorimeter (DSC) results showed that the fully charged spinel with lithium doping has better thermal stability.

Effect of lithium additive on the microstructure and electrical responses of 0.9PMN–0.1PT ceramics

Structural effects of lithium additive on 0.9PMN–0.1PT powders prepared by Ti-modified columbite route were studied. The substitution of Li+ ions for Mg2+ ions in the B-site sub-lattice of 0.9PMN–0.1PT perovskite structure was explained in terms of lead and oxygen vacancies generation originated as consequence of the ionic compensation of negatively charged Li′Mg sites. The rise in mass transport as consequence of the increasing of Pb2+ and O2− vacancies produces more agglomerated particles during the powder synthesis and changes the mechanical characteristics between grain and grain boundary of sintered ceramic. The relation between K m and T m values, the difference between ionic radii of B cation and the molar volume were used to explain the changes in the relaxor behavior and diffusiveness of phase transition as function of lithium doping, which are corroborated by the results obtained through the ferroelectric characterization.

English

Doping of lithium (Li+) cations results in stabilised zirconia, especially in tetragonal (t)crystal structure, i.e., Li+: t-ZrO2. It is useful to vary oxygen vacancies in Li+: ZrO2 powders. TheLi+: t-ZrO2 powder having 1-5 mol per cent Li+, are obtained by using a novel chemical methodof a polymer precursor, which consists of Li+ and Zr4+ cations capping in polymer molecules ofpolyvinyl alcohol (PVA) and sucrose. The results are analysed in terms of XRD and microstructureof Li+: t-ZrO2 powders prepared under specific conditions of heating the precursor in air atelevated temperatures. The polymer precursor consists of fibrils of average 120 m length and0.5–1.0 m dia. A refined Li+: t-ZrO2 powder (15-25 nm crystallite size) occurs after heating theprecursor at 500–600 °C for 2 h in air.

Computational Investigation of Adsorption of Molecular Hydrogen on Lithium-Doped Corannulene

Density functional theory and classical molecular dynamics simulations are used to investigate the prospect of lithium-doped corannulene as adsorbent material for H(2) gas. Potential energy surface scans at the level of B3LYP/6-311G(d,p) show an enhanced interaction of molecular hydrogen with lithium-atom-doped corannulene complexes with respect to that found in undoped corannulene. MP2(FC)/6-31G(d,p) optimizations of 4H(2)-(Li(2)-C(20)H(10)) yield H(2) binding energies of -1.48 kcal/mol for the H(2)-Li interaction and -0.92 kcal/mol for the H(2)-C interaction, whereas values of -0.94 and -0.83 kcal/mol were reported (J. Phys. Chem. B 2006, 110, 7688-7694) for physisorption of H(2) on the concave and the convex side of corannulene using MP2(full)/6-31G(d), respectively. Classical molecular dynamics simulations predict hydrogen uptakes in Li-doped corannulene assemblies that are significantly enhanced with respect to that found in undoped molecules, and the hydrogen uptake ability is dependent on the concentration of lithium dopant. For the Li(6)-C(20)H(10) complex, a hydrogen uptake of 4.58 wt % at 300 K and 230 bar is obtained when the adsorbent molecules are arranged in stack configurations separated by 6.5 A, and with interlayer distances of 10 A, hydrogen uptake reaches 6.5 wt % at 300 K and 215 bar.

Effects of Lithium Doping and Post-processing on the Cathodoluminescence of Zinc Oxide Nanoparticles

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Lithium doping of pentacene for electrochemical hydrogen storage

This study reports in detail the practical realization of electrochemical hydrogen storage in porous metal-incorporated nanostructured organic compounds, Li-doped pentacene, which has been synthesized by potentiostatic electrolysis and characterized by x-ray diffraction, Fourier transform infrared spectra analysis, and galvanostatic current charge-discharge measurements. Although the lithium doping is at a very low level the conductivity of pentacene increases considerably after the doping, which makes the ordered layer-stacked Li-doped pentacene very promising as electrode material for electrochemical hydrogen storage, and a discharge capacity of ca. 239mAh∕g (corresponding to 0.89wt% hydrogen storage) has been achieved for the Li-doped pentacene electrode.

Experimental Attempt of Lithium Doping to Impurity-Free Single-Walled Carbon Nanotubes Obtained by Highly Efficient Synthesis Method

not Available.

Electrochemical hydrogen storage in Li-doped pentacene

Porous metal-incorporated nanostructured organic compounds represent an innovative concept in hydrogen storage. This work reports in detail the first practical realization of electrochemical hydrogen storage in such a material, Li-doped pentacene. Although lithium doping is at a very low level the conductivity of pentacene increases considerably after the doping of lithium, which makes ordered layer-stacked Li-doped pentacene very promising as electrode material for electrochemical hydrogen storage. A discharge capacity of ca. 238 mA h g(-1) has been achieved in 6M KOH for the Li-doped pentacene electrode, which is comparable to that obtained from commonly used electrode material, LaNi5 alloy for electrochemical hydrogen storage. Furthermore, a great improvement in the hydrogen storage capacity can be expected from the Li-doped pentacene by simply raising the lithium doping level.

Voltammetric study of Bphen electron-transport layer in contact with LiF∕Al cathode in organic light-emitting diodes

We report that the similarities of I-V characteristics of organic light-emitting diodes (OLEDs) incorporating Bphen (4,7-diphenyl-1,10-phenanthroline) electron-transport layer, with or without lithium doping, do not stem from the analogous compositions of the respective electron-transport layers. Voltammetric studies of OLED devices of the following general structure: anode ∣ NPB (N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine) ∣ TBADN (9,10-bis(2-naphthyl)-2-t-butylanthracene) ∣ Bphen ∣ LiF ∣ Al, indicate that the bulk of the Bphen electron-transport layer has insulating rather than semiconducting properties. A previously unknown feature is also detected by voltammetry: the presence of a macroscopic dipole comprised of a negative interfacial charge at the NPB ∣ TBADN interface and a positive charge in the Bphen layer and∕or at the TBADN ∣ Bphen interface, which could result from the diffusion of lithium ions. We also find that, in contrast to the bulk of the Bphen layer, its thin sublayer has, in fact, semiconducting properties, which also could be reasonably explained by the diffusion of lithium ions along with the migration of a countercharge, e.g., electron hopping between Bphen molecules.

Crystallinity and morphology dependent luminescence of Li-doped Y2−xGdxO3:Eu3+ thin film phosphors

Abstract The influence of lithium doping on the crystallization, the surface morphology, and the luminescent properties of pulsed laser deposited Y 2− x Gd x O 3 :Eu 3+ thin film phosphors was investigated. The crystallinity, the surface morphology, and the photoluminescence (PL) of films depended highly on the Li-doping and the Gd content. The relationship between the crystalline and morphological structures and the luminescent properties was studied, and Li + doping was found to effectively enhance not only the crystallinity but also the luminescent brightness of Y 2− x Gd x O 3 :Eu 3+ thin films. In particular, the incorporation of Li and Gd into the Y 2 O 3 lattice could induce remarkable increase in the PL. The highest emission intensity was observed Li-doped Y 1.35 Gd 0.6 O 3 :Eu 3+ thin films whose brightness was increased by a factor of 4.6 in comparison with that of Li-doped Y 2 O 3 :Eu 3+ thin films.

Advanced Dielectric Properties of Li2O Doped 0.2[Pb(Mg1/3Nb2/3)]-0.8[PbTiO3-PbZrO3] Ceramics

0.2Pb(Mg 1/3 Nb 2/3 )O 3 -0.8Pb(Zr 0.475 Ti 0.525 )O 3 [PMNZT] ceramics doped with various contents of Li 2 O (0, 0.05, 0.1, 0.2, 0.3 wt.%) are fabricated by columbite precursor method. The lithium doping effect on the PMNZT ceramics is discussed in the relation to the piezoelectric properties and conduction behavior. The ferroelectricity is confirmed by polarization-electric field hysteresis loop. Remnant polarization P r reached a maximum value of 27.16 μC/cm 2 when a 0.1 wt% Li 2 O was doped. Coercive field E c reached a maximum value of 8.27 kV/cm for 0.1 wt% Li 2 O and decreased again as Li 2 O ratio increased. The PMNZT + 0.1 wt.% Li 2 O ceramic attain the sufficient densification with large dielectric constant (ϵ r = 1448) and low dielectric loss (tan δ = 0.022) at room temperature. The maximum values of the longitudinal electromechanical coupling factor (k 33 ) and piezoelectric coefficient (d 33 ) of PMNZT + 0.1 wt.% Li 2 O ceramics are 78% and 565pC/N, respectively. The incorporation of Li+1 in the PMNZT ceramics has led to an appreciable reduction in conductivity throughout the temperature range of 30∼400°C. The activation energy of PMNZT + xLi 2 O ceramics calculated from the Arrhenius relation were (x = 0, 0.05, 0.1, 0.2, 0.3) were 1.05, 1.25, 1.27, 1.38 and 1.41 eV, respectively.

Electrochemical lithium doping of a pentacene molecule semiconductor

Li-doped pentacene has been developed by using an electrochemical approach; that is, constant-potential electrolysis. Li-doped pentacene was characterized by Raman spectrometry and x-ray diffraction measurements. Lithium doping introduces a modification of the C–H vibrational modes located at the end of pentacene molecules. A low doping level has been observed for electrochemical synthesis of Li-doped pentacene, and lithium species are supposed to be intercalated between the two-dimensional pentacene layers. The lithium-doped pentacene exhibits a conductivity of ∼6×10−3Scm−1.

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.

Transition from one-dimensional to three-dimensional behavior induced by lithium doping in single wall carbon nanotubes

The electronic properties of Li doped single-wall carbon nanotubes were studied by high-resolution photoemission spectroscopy. Upon Li intercalation, the limited displacement of the Fermi level agrees with a partial charge transfer of the Li2s electron to the $\mathrm{C}2p\text{\ensuremath{-}}{\ensuremath{\pi}}^{*}$ states. The increase of the density of states near the Fermi level with Li concentration suggests a transition from the one-dimensional Tomonaga-Luttinger liquid behavior, observed in the pristine nanotubes, to three-dimensional transport properties in the doped sample. The increased spectral weight near the Fermi level can be also partly ascribed to the formation of new states in the conduction band due to the hybridization between Li and C.

Luminescence properties of Li + doped nanosized SnO 2:Eu

The influence of lithium doping on the crystallization behavior, morphology, and enhancement in photoluminescence intensity of SnO 2:Eu was investigated. In order to attain high homogeneous and pure samples, the Pechini type sol–gel method was adopted for the synthesis at low temperature (500 °C). The structure and morphology were characterized by using X-ray diffraction (XRD) and transmission electron microscope (TEM). The results indicate that the Li + doping could accelerate the crystallization of SnO 2 and the particle size of the phosphors is below 100 nm. In particularly, the incorporation of Li + ions into SnO 2 lattice could induce a remarkable increase of photoluminescence intensity.