Mössbauer and ESR investigation of the behaviour of iron in vanadium borophosphate glasses

Mössbauer and ESR measurements were performed on vanadium borophosphate glasses containing iron. The glass composition was 78 mole% V₂O₅, 15 mole% P₂O₅, 7 mole% B₂O₃ and different amounts of Fe₂O₃ (0.5–50 mole%) were added. The relative percentage of iron in different states and site positions could be determined for each glass composition. Correlation between the behaviour of iron and its variation in structural units and other physical properties are proposed. A maximum amount of 33 mole% Fe₂O₃ could be incorporated in the glass network, higher concentrations lead to the precipitation of α-Fe₂O₃.     

Hydrothermal synthesis of spinel Li1+x Mn2O4 as cathode material for rechargeable lithium battery

Abstract

The hydrothermal synthesis of Li-Mn spinel oxide (Li_1+xMn₂O₄) was undertaken in order to develop high quality, low cost cathode material for a rechargeable lithium battery. In our experiments, γ-MnOOH, LiOH · H₂O and H₂O₂ were used as starting materials to synthesize Li-Mn spinel oxide under hydrothermal conditions of 180-230°C and about 1.0-2.8 MPa. The chemical composition and particle size of the Li_1+xMn₂O₄ is easily controlled in the hydrothermal reaction. The Li_1+xMn₂O₄ produced was characterized by X-ray diffraction, with the spinel phase having a Li/Mn ratio of 0.50-0.60. There is convincing evidence, as a result of this work, that our synthesis process is most suitable for producing high quality cathode material that can be used in a rechargeable lithium battery.     

Correlations entre la conductivite ionique et la concentration en ions alcalins dans les borates de lithium vitreux

The electrical transport properties of the B₂O₃ - xLi₂O glasses have been investigated. An electrochemical approach allows to give an interpretation of the conductivity based on the carrier concentration in relation with Li₂O content. The mobility of the Li⁺ ions does not seem to depend on the composition.     

Crystal structure analysis of Li<Subscript>3</Subscript>PO<Subscript>4</Subscript> powder prepared by wet chemical reaction and solid-state reaction by using X-ray diffraction (XRD)

Lithium phosphate (Li₃PO₄) is one of the promising solid electrolyte materials for lithium-ion battery because of its high ionic conductivity. A crystalline form of Li₃PO₄ had been prepared by two different methods. The first method was wet chemical reaction between LiOH and H₃PO₄, and the second method was solid-state reaction between Li₂O and P₂O₅. Crystal structure of Li₃PO₄ white powder had been investigated by using an X-ray diffraction (XRD) analysis. The results show that Li₃PO₄ prepared by wet chemical reaction belongs to orthorhombic unit cell of β-Li₃PO₄ with space group Pmn2₁. Meanwhile, Li₃PO₄ powder prepared by solid-state reaction belongs to orthorhombic unit cell of γ-Li₃PO₄ with space group Pmnb and another unknown phase of Li₄P₂O₇. The impurity of Li₄P₂O₇ was due to phase transformation in solid state reaction during quenching of molten mixture from high temperature. Ionic conductivity of Li₃PO₄ prepared by solid-state reaction was ～3.10^?7 S/cm, which was higher than Li₃PO₄ prepared by wet chemical reaction ～4.10^?8 S/cm. This increasing ionic conductivity may due to mixed crystal structures that increased Li-ion mobility in Li₃PO₄.     

Li2O-(LiCl)2-B2O3-Al2O3系统玻璃的Raman光谱研究

我们用Raman光谱研究了Li₂O(LiCl)₂B₂O₃-Al₂O₃系玻璃的结构,着重研究了Al₂O₃的影响。对于Li₂O-B₂O₃系玻璃,Li₂O含量增加使玻璃中存在的BO₃三角体转变为BO₄四面体, 关键词：     

Synthesis and characterization of nanostructured Li2MnO3 from nanostructured MnOOH precursors

Li₂MnO₃ with different nanostructures was synthesized through a solid-state reaction. MnOOH nanorods and nanowires prepared via the hydrothermal method were used as precursors, respectively, to react with Li(OH)·H₂O to prepare nanostructured Li₂MnO₃ in the temperature range from 500 to 800 °C. The samples were characterized by XRD, TEM, ESR and FTIR results. Based on the experimental results, the dehydration-oxidation-combination (DOC) formation mechanism of Li₂MnO₃ was proposed.     

Investigation of ferroelectric transitions in the binary system LiTaO3 [sbnd] Fe2O3

Abstract

A continuous solid solution with the formula Li_1?XTa_1?XFe_2XO₃ O≤x≤. 125 has been identified. Hexagonal a_H axis decreases very slightly with increasing Fe₂O₃ content whereas simultaneously c_H passes through a maximum at x =.06. This behaviour has been tentatively explained on the basis of repulsive forces. The ferroelectric Curie temperature decreases as the composition deviates from LiTaO₃.     

Hole doping by Li substitution and antiferromagnetism in YBa Cu O studied by neutron powder diffraction measurements

The magnetic structure of tetragonal insulating YBa₂Cu_3-xLi_xO_y has been studied as a function of x and y. The Néel temperature and the mean ordered magnetic moment on the Cu2 sites were determined by neutron powder diffraction measurements. The decrease of these two parameters as compared to YBa₂Cu₃O₆ is much stronger for lithium than for zinc substitution. The difference is quantitatively explained by the presence of holes created in the CuO₂ planes. These holes arise from the substitution of plane Cu²⁺ by Li⁺. We suggest an explanation why such holes are not seen for the same substitution of plane Cu²⁺ by Li⁺ in orthorhombic superconducting YBa₂Cu_3-xLi_xO _{7 - δ} . Received 31 October 2001 and Received in final form 6 March 2002 Published online 25 June 2002     

Investigation of Li-induced structural disorder and phase transition in ZnO by Raman spectroscopy

Zn_0.8Li_0.2O ceramics with wurtzite structure have been fabricated by a solid reaction of ZnO and Li₂CO₃. The effects of substitutional Li atoms on the crystal structure and structural phase transition of ZnO are studied by Raman spectroscopy. The enhancement of E₁(LO) mode in Zn_0.8Li_0.2O ceramics reveals the occurrence of Li-induced structural disorder. Temperature dependent Raman spectra strongly indicate that a structural phase transition occurs at about 448 K in Zn_0.8Li_0.2O ceramics.     

Characterization of stoichiometric LiNbO3 grown from melts containing K2O

The growth of LiNbO₃ single crystals from a melt with the Li/Nb ratio of 0.946, to which 6 wt.% K₂O has been added, leads to stoichiometric specimens, essentially free of potassium, with (50±0.15) mol% Li₂O in the crystal. This is established by studying the composition dependence of the following properties: linewidths of the electron paramagnetic resonance (EPR) of Fe³⁺, energy of the fundamental absorption edge, Raman linewidths of phonon modes, and dispersion of the optical birefringence. Comparison of the results with relevant calibration scales leads to the above composition. In all cases the Li₂O content was found to be closer to 50% than that of a LiNbO₃ crystal vapor-phase equilibrated to 49.9mol% Li₂O. The photorefractive effect at light intensities I10⁷ W/m² is suppressed in this stoichiometric material. The features of the ternary system K₂O-Li₂O-Nb₂O₅, which are possibly responsible for the unexpected growth of stoichiometric LiNbO₃ from the indicated melts, are discussed.     

Bulk GaN single crystals: a reinvestigation of growth mechanism using Li3N flux

The GaN growth mechanism using Li₃N flux was reinvestigated by designing a new experiment that allowed us to grow GaN simultaneously under varying Ga/Li₃N molar ratios. The results confirm the two-step reactions involved in the Ga–Li₃N system: Li₃N+Ga→Li₃GaN₂+Li (1) and Li₃GaN₂+Ga→GaN+Li (2). It is found that reaction (2) is the main cause leading to small GaN crystals in the products. Larger GaN crystals, however, can grow by a different pathway. The growing process is concerned with the formation of Li–Ga–N melt by dissolving Li₃GaN₂ in Li–Ga melt after reaction (1). GaN crystals up to 3 mm grow from the Li–Ga–N melt upon cooling on the GaN particles by reaction (2). Our results suggest that it is necessary to restrain reaction (2) by choosing proper Ga/Li₃N molar ratios so as to obtain GaN crystals in larger size. PACS 81.05.Ea; 81.10.Dn     

The effects of Li2CO3 particle size on the properties of lithium titanate as anode material for lithium-ion batteries

Spinel structured Li₄Ti₅O₁₂ was synthesized by a solid-state method using TiO₂ and Li₂CO₃ as starting materials. High-energy ball milling was used to obtain the Li₂CO₃ samples with different particle size. Then, the effects of Li₂CO₃ particle size on the structure, morphology, and electrochemical performance of Li₄Ti₅O₁₂ samples were investigated in detail. The samples were characterized by TG/DTA analysis, X-ray diffraction, scanning electron microscopy and electrochemical tests, respectively. The results indicate that fine Li₂CO₃ particles will promote the interfacial reaction between Li₂CO₃ and TiO₂ in solid-state reaction. The crystallinity and particle size of Li₄Ti₅O₁₂ depend on the particle size of Li₂CO₃. Electrochemical tests show that Li₄Ti₅O₁₂ samples synthesized by fine Li₂CO₃ particles exhibit better rate capacity and cycle performance.     

Correlation between Li+ adsorption capacity and the preparation conditions of spinel lithium manganese precursor

Spinel lithium manganese oxides can be used as Li⁺ adsorbent with topotactical extraction of lithium. In this paper, the solid state methods were introduced to prepare spinel lithium manganese precursors with Li₂CO₃ and LiOH·H₂O as different Li sources. The Li⁺ uptake was studied to clarify the correction between Li⁺ adsorption capacity and the preparation conditions of precursors, including different Li sources, Li/Mn mole ratios and heating time. The results indicated that the Li⁺-extracted materials prepared with LiOH·H₂O and MnCO₃ usually have higher Li⁺ adsorption capacity than Li₂CO₃ and MnCO₃, and an ascending trend was found in Li⁺ uptake with increasing Li/Mn mole ratio in the preparation of the precursor, but it is not proportional. The Mn₂O₃ impurities could be the primary reason for decreasing Li⁺ adsorption capacity. Furthermore, it is concluded that the Li⁺-extracted materials obtained from spinel manganese oxides synthesized with Li/Mn = 1.0 can serve as selective Li⁺ absorbents due to its high selectivity and large adsorption capacity.     

Structural and electrochemical effects of cobalt doping on lithium manganese oxide spinel

Pure LiMn₂O₄ and lithium manganese oxide spinels with partial replacement of manganese by cobalt up to 20 mole%, LiCo_xMn_2−xO₄, were prepared. The effect of extended cycling on the crystal structure was investigated. A capacity decrease with increasing cobalt content was observed in the potential range about 4100 mV vs. Li/Li⁺. Cycling behavior is significantly improved, compared to LiMn₂O₄. LiCo_xMn_2−xO₄ is discharged in a single phase reaction in the upper potential range around 4100 mV vs. Li/Li⁺, whereas pure LiMn₂O₄ shows a two phase behavior. LiMn₂O₄ shows a significant broadening of peaks in plots of differential capacity and change in shape of the voltage profile upon extended cycling. LiCo_xMn_2−xO₄ shows neither broadening nor change. Voltage profiles and plots of the differential capacity differ significantly compared to spinels with lithium substitution, Li_1+xMn_2−xO₄. In contrast to Li_1+xMn_2-xO₄, LiCo_xMn_2-xO₄ is discharged in a two step process in the range of 0 ≤ × ≤ 0,5. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Mössbauer and electron spin resonance investigation of the effect of heat treatment on the structural units and magnetic properties of iron vanadium borophosphate glasses

In our previous work /1/, the behaviour of iron addition to vanadium borophosphate (V. B. P.) glasses (78 mole% V₂O₅, 15 mole% P₂O₅, 7 mole% B₂O₃ and x mole% Fe₂O₃ where (0.5≤x≤50) was investigated by (ME) and (ESR) techniques. In the present work, the investigations were extended to study the effect of heat treatment (H. T) on the same system (up to x=7.5 mole% Fe₂O₃). The results obtained showed that heating these glasses at the glass transition temperature (Tg=350°C) for different periods up to 120 min. highly affected their structural units and magnetic properties. The extent of this effect depends on the iron content as well as on the H. T period.     

Thermoluminescence of B2O3-Li2O glass system doped with MgO

Lithium borate (LiB) glasses in the system (100−x)B₂O₃-xLi₂O with x=20, 30, 40, 50, 60 and 70 mol% were prepared. The glasses were doped with different concentrations of the order of 10⁻¹, 10⁻², 10⁻³, 10⁻⁴ and 10⁻⁵ of MgO and their thermoluminescent (TL) response was investigated. The irradiations were performed using γ rays from a ⁶⁰Co source in the dose range from 0.1 to 25 kGy. The material displayed good sensitivity for γ-rays and intensity of TL signals is dependent on γ-ray dose and Li₂O content. For each dose level and investigated temperature range (50-350 °C), exactly single isolated glow peak appears in the temperature range of 165-205 °C depending on both Li₂O concentrations and time of exposure. The shape of the glow peak has altered significantly with increase in the gamma ray dose or Li₂O concentrations. The glass composition with x=50 mol% doped with 10⁻³ mol% of MgO presented the best TL response. The results of the present study indicated that the recorded single and isolated high temperature peak is a good candidate for TL dosimetric investigations. This indicates that 50 B₂O₃-50Li₂O-doped with 10⁻³ mol% of MgO is possibly used as materials for radiation dosimetry in the dose range of 0.1-20 kGy.     

Enthalpy of formation of LiNiO2, LiCoO2 and their solid solution,LiNi1−xCoxO2

LiCoO₂, LiNiO₂ and their solid solution, LiNi_1−xCo_xO₂, are important cathode materials for lithium ion batteries. Samples in this system were synthesized by solid state reaction of Co₃O₄, NiO and Li₂CO₃ or LiOH·H₂O. Their lattice parameters were determined by Rietveld refinement. High temperature drop solution calorimetry in molten 3Na₂O·4MoO₃ and 2PbO·B₂O₃ solvents at 974 K was performed to determine the enthalpy of formation from the constituent oxides plus oxygen and the enthalpy of mixing in the solid solution series. There are approximately linear correlations between the lattice parameters, the enthalpy of formation from oxides (Li₂O, NiO and CoO) plus O₂ and the Co content in the compounds. The solid solution of LiCoO₂ and LiNiO₂ is almost ideal, showing a small positive enthalpy of mixing. The enthalpy of formation of LiCoO₂ from oxides (Li₂O, NiO and CoO) and oxygen at 298 K is −142.5±1.7 kJ/mol (from sodium molybdate calorimetry) or −140.2±2.3 kJ/mol (from lead borate calorimetry). That of LiNiO₂ is −56.2±1.5 kJ/mol (from sodium molybdate calorimetry) or −53.4±1.7 kJ/mol (from lead borate calorimetry). The cobalt compound is thus significantly more stable than its nickel analogue. The phase assemblage LiCoO₂, Li₂O and CoO is seen at a lower oxygen pressure at constant temperature than the assemblage Co₃O₄/CoO, reflecting the stabilization of Co(III) in the ternary Li–Co–O system.     

The influence of lithium excess in the target on the properties and compositions of Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>2</Subscript>O<Subscript>4−<Emphasis Type="Italic">δ</Emphasis></Subscript> thin films prepared by PLD

Li–Mn–O thin films were deposited by pulsed laser deposition (PLD) onto stainless steel substrates using targets containing different concentrations of added Li₂O. The influence of the target composition on the stoichiometry of the resulting thin films, the surface morphology and the electrochemical properties was studied. The application of the target with added 7.5 mol% Li₂O results in an almost ideal lithium content, while all films were still oxygen deficient. The thin films were applied as electrodes in Li//Li_1+x Mn₂O_4−δ cells (i.e. model cells for a rechargeable Li-ion battery) and characterized by cyclic voltammetry and galvanostatic charge/discharge experiments. The electrochemical measurements of the thin films confirmed that the thin films can serve as good model systems and that they show a sufficient cyclability.     

Hypersonic secondary relaxation due to fast ion diffusion modes in xLiCl0.5Li2OB2O3 glasses

The hypersonic attenuation and the sound velocity for a high and a low conducting Li⁺-glass, 0.7LiCl0.5Li₂OB₂O₃ and 0.5Li₂OB₂O₃, respectively, have been measured as functions of temperature by Brillouin scattering. A large excess hypersonic attenuation was found at high temperatures in the LiCl rich glass compared to the low conducting glass. The effect is attributed to structural relaxation of fast ion diffusion modes involving Li⁺ ions jumping between different sites in the glass network. The sound velocity observed for the LiCl doped glass was 10% lower than the value for the undoped glass. This reflects considerable changes in the elastic properties of the glass network in accordance with a model which proposes that the high conductivity in these glasses can be explained by structural changes of the intermediate range order.     

Raman and FTIR spectroscopy study of LiFeTiO<Subscript>4</Subscript> and Li<Subscript>2</Subscript>FeTiO<Subscript>4</Subscript>

We report the Fourier transform infrared (FTIR)–Raman spectroscopy study of spinel Li–Fe–Ti–O oxides viz., LiFeTiO₄ and Li₂FeTiO₄ in order to probe structural details such as type of bonding networks viz., octahedral and tetrahedral, and type of different atomic bonds present in those materials. Both the samples were prepared through solid-state reaction route prior to high-energy ball-milling. All the phases prepared through solid-state reaction and ball-milled were probed using X-ray diffraction, field emission scanning electron microscopy, and FTIR–Raman spectroscopy. X-ray diffraction study indicates spinel phase formation with Fd3m space group symmetry for both LiFeTiO₄ and Li₂FeTiO₄. However, pure phase of Li₂FeTiO₄ was not achieved in these preparation routes, rather mixed phases of Li₂FeTiO₄ and Fe₂TiO₄ were achieved. Field emission scanning electron microscopy (FESEM) analysis indicated porous microstructure for LiFeTiO₄ while more agglomerated microstructure for Li₂FeTiO₄. Ball-milling reduces the grain size partly for both the samples. FTIR–Raman spectroscopy indicates the presence of LiO₄ tetrahedral, LiO₆ and TiO₆ octahedral in the spinel network. Presence of Li–Li–O type bonding was also indicated from spectroscopy analysis. Existence of Fe₂TiO₄ phase with Li₂FeTiO₄ was also identified from both FTIR and Raman spectrum. Effect of ball-milling on the spectrum has been exhibited by broadening and peak shifting the FTIR–Raman spectrum, arising from the enhanced lattice strain and structural disorder.