Etude par resonance paramagnetique electronique des verres du systeme B2O3-Na2O-Na3PO4

An EPR study of fast Na⁺ ion vitreous conductors of the system B₂O₃?Na₂O?Na₃PO₄ has been carried out. After X-ray irradiation two types of paramagnetic centers have been observed. The first one is of boron-oxygen hole center (B.O.H.C.) type and similar to that earlier observed for other alkali borate glasses. The second one is of PO₄^2? type. A simulation of its spectrum has been achieved and a defect model discussed.     

LiF-LiCl-B2O3系统非晶态快离子导体结构的研究

本文通过对¹¹B核磁共振(¹¹B-NMR)、红外光谱等实验方法,研究了LiF-LiCl-B₂O₃三元系统玻璃的结构和离子导电性,着重于F^-离子在玻璃网络中所起的作用,以及F^-,Cl^-和Li⁺离子对导电率的影响。LiF-LiCl-B₂O₃三元系统玻璃,随LiF含量的增加,B由三角体向四面体变化,从而F^-离子进入网络,使玻璃结构由[B₂O₃]三角体层状结构向三维空间延展,形成了含有[BO₃F]基团的三维空间网络,Cl^-离子以游离的离子存在于网络中,起着松散网络的作用,对提高电导率有利,而Li⁺离子作为传导离子,对电导率的贡献是主要的。本系统玻璃的电导率是随LiF,LiCl含量的增加而增大,在300℃时测得电导率σ=6.12×10^-4Ω^-1·cm^-1。 关键词：     

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.     

Solid solutions Li1+xV3O8 as cathodes for high rate secondary Li batteries

Following a preliminary investigation, Li/Li_1+xV₃O₈ cells have been examined. Using samples of low x content, up to 3 eq Li⁺ could be accepted both chemically and electrochemically by one mole of active material. Li⁺ is accomodated in the tetrahedral sites existing between the (V₃O₈)^(1+x)- layers. Li⁺ jumping from site to site is fast and permits high rate capabilities: at 10 mA/cm², 1.1 eq Li⁺ per mole could still be inserted. The structure does not show irreversible alterations upon extended lithiation, allowing long cycle lives to be achieved. Kinetic constraints limit the recovery of the full capacity of the first discharge at medium-high rates, but the second-discharge capacity declines slowly with cycle number.     

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：     

Li2O-B2O3-SiO2系统玻璃的Raman光谱研究

在Li₂O≥30mol％的Li₂O-B₂O₃-SiO₂系统玻璃中,以Li₂O代B₂O₃或SiO₂都导致玻璃网络中带非桥氧的硼酸盐和硅酸盐基团的量的增加;以B₂O₃代SiO₂则使玻璃网络中带和不带非桥氧的硼酸盐基团以及带非桥氧的硅酸盐基团的量都增加。 关键词：     

Low temperature EPR study of the “impurity” resonances in (TCNQ)- and (TCNQ)-2 salts

The so-called “impurity” resonances in polycrystalline Li⁺ (TCNQ)^-, Cu⁺ (TCNQ)^- and Cu⁺ (TCNQ)^-₂ have been studied at liquid helium-temperatures. The Li⁺ (TCNQ)^- resonance is partially resolved at low microwave powers with g_⊥ = 2.0025 ± 0.0005 and g_∥ = 2.008 ± 0.001. Itis found that the (TCNQ) and (TCNQ)^-₂ complexes give characteristics spectra. The possible origin of these resonances is discussed.     

Effect of ZnO/CdO on the structure and electrical conductivity in Li2O·MO·Bi2O3·B2O3 glasses (M=Zn, Cd)

Studies of structural and electrical properties have been carried out on a number of glasses with wide ranging compositions in the glass systems Li₂O·MO·Bi₂O₃·B₂O₃ (where M=Zn or Cd), in order to understand the effect of transition metal (TM) ions on the structure of these glasses. The density and molar volume measurements have also been made to understand the structural changes occurring in these glasses. The dc conductivity measured in the temperature range 423-623 K obeys Arrhenius law. It increases with increase in Li₂O/MO ratio. The results of infrared spectra indicate that TM ions (Zn²⁺ or Cd²⁺) behave as network former in the present system. Boron exists in both tri- and tetra-hedral units in these glasses and no boroxol ring formation takes place in the glass structure. Values of theoretical optical basicity have also been reported.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Li2B4O7晶体的晶格振动光谱

在室温下测量了Li₂B₄O₇单晶的各种振动类的偏振Raman散射谱和该晶体粉末样品的红外吸收谱(200—4000cm^-1)。根据LO-TO劈裂的实验结果,计算出该晶体极化模的有效电荷和振子强度。通过与BBO和LBO晶体的结构和B—O伸缩振动模频率比较,得出:Li₂B₄O₇晶体可能有较大的非线性光学系数。 关键词：     

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.     

MO2,M2O5和MO3氧化物对锂硼酸盐玻璃离子导电性的影响

本工作测量了45Li₂O·50B₂O₃·5M_mO_n(M=Al,Ti,Zr,P,V,Nb,Ta,Cr,Mo,W)玻璃的总电导率和电子电导率,以Raman光谱研究了玻璃结构,依据作为锂离子定域体的阴离子团的性质讨论了MO₂,M₂O₃和MO₃氧化物对玻璃离子导电性的影响。 关键词：     

Transport processes in heavy metal fluoride glasses

Na self-diffusion, Li self-diffusion, Na⁺–Li⁺ ion exchange, electrical conductivity, and mechanical relaxation have been studied below T_g on glasses of the system ZrF₄–BaF₂–LaF₃–AF (A=Na, Li), with A=10, 20, 30 mol%. Compared to the transport mechanism in alkali-containing silicate glasses, the mechanisms in these non-oxide glasses are anomalous. Thus the self-diffusion coefficient of Na decreases with increasing NaF content, whereas that of Li increases with increasing LiF content. Both the electrical conductivity and the Na⁺–Li⁺ ion exchange reach a minimum at ≈ 20 mol% LiF, and the mechanical relaxation shows one peak for the 20 and 30 mol% LiF-glasses and two peaks for the glass with 10 mol% LiF, evidencing both a contribution of F⁻ and Li⁺ ions to the transport. Moreover, the presence of the three partially interacting mobile species F⁻, Na⁺, Li⁺ obviously leads to an anionic–cationic mixed ion effect. Applying the Nernst–Einstein equation to the Li⁺ transport in LiF-containing glasses shows that its mechanism is dissimilar to that in oxide glasses. Calculated short jump distances possibly can be interpreted as an Li⁺ movement via energetically suitable sites near F⁻ ions. Likewise the Nernst–Planck model, successfully applied to the ionic transport in mixed alkali silicate glasses, obviously does also not hold for the present heavy metal fluoride glasses.     

Ionic lithium conductivity in sulphur base glasses. 7Li NMR study of xLi2S−(1−x)GeS2 system

The lithium mobility in glasses of composition xLi₂S?(1?x)GeS₂ has been followed by c.w. (for x = 0.3; 0.4 and 0.5) and pulsed NMR (for x = 0.3 and 0.5) between ? 150 and + 280°C.The second moment of the resonance line of ⁷Li(0.89–1.51 G²) is proportional to the molar fraction of Li₂S, which may be correlated to an homogeneous Li nuclei distribution.The resonance line profiles and their thermal evolution seem to show that some Li⁺ ions do not participate in the conduction.Thermal variation of the spin-lattice relaxation time T₁, shows a strongly asymmetrical shape, if one considers In $\text{T}{}^{\mathrm{?1}}{}_1\text{= ?(T}{}^{\mathrm{?1}}\text{)}$ on both sides of the observed maxima. This behaviour may be explained by a distribution of the Li correlation times τ corresponding to different jump distances between various possible sites. The Cole-Davidson model allows the best agreement between experimental and theoretical values of the correlation times.The activation energies deduced from this model are close to those obtained from conductivity measurements (0.43 eV by NMR, 0.56 eV by conductivity determinations for x = 0.50), they may be correlated to the longer Li⁺ jumps in the vitreous matrix.     

Effect of Bi2O3 content on physical and optical properties of 15Li2O-15K2O-xBi2O3-(65−x) B2O3: 5V2O5 glass system

Multi-component bismuth borate glasses doped with vanadium ions 15Li₂O-15K₂O-xBi₂O₃-(65−x) B₂O₃: 5V₂O_5, (x=3, 5, 7, 10, 12 and 15) have been prepared using conventional melt quench technique. Characterization of the prepared glasses has been done using X-ray diffraction, differential scanning calorimetry and density measurements. The effect of Bi₂O₃ content on the optical properties of the present glass system is studied from the optical absorption spectra recorded in the wavelength range 200-800 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The values of optical band gap for indirect allowed transitions have been determined using available theories. The origin of the Urbach energy is associated with the phonon-assisted indirect transitions. The density and molar volume studies indicate that Bi₂O₃ in these glasses is acting partly as network modifier and partly as network former. The variations in the optical band gap energies, density and molar volume with Bi₂O₃ content have been discussed in terms of changes in the glass structure. Values of the theoretical optical basicity, average crosslink density and the average electronic polarizability are also reported.     

Effect of Li2O content on physical and structural properties of vanadyl doped alkali zinc borate glasses

The effect of Li₂O content in vanadyl doped 20ZnO+xLi₂O+(30−x)Na₂O+50B₂O₃ (5≤x≥25) glasses has been studied with respect to their physical and structural properties. The absence of sharp peaks in XRD spectra of these glass samples confirms the amorphous nature. The physical parameters like density, refractive index, ionic concentration and electronic polarizability vary non-linearly with x mol% depending on the diffusivities of alkali ions. EPR and optical absorption spectra reveal that the resonance signals are characteristics of VO²⁺ ions in tetragonally compressed octahedral site. Spin-Hamiltonian, crystal field, tetragonal field and bonding parameters are found to be in good agreement with the other reported glass systems. The tetragonal distortion (g_⊥-g_∥) and Dt reveals that their values vary non-linearly with Li₂O content and reaches a minimum at x=10 mol%. An anomaly of character has been observed in all the properties of vanadyl doped glass systems, which gives a clear indication of mixed alkali effect.     

Laser photoluminescence spectra of the M+S2− species in solid argon at 12K

Matrix reactions of alkali metal atoms with S₂Cl₂ and photolyzed H₂S samples have been examined by laser excitation at 457.9 nm. The strong photoluminescence spectrum from 12 300 to 18 300 cm^?1 exhibited vibrational spacings near 550 cm^?1. Observation of the same ZPL spectrum with two different precursors identified the carrier as Na⁺S₂^?. The vibrational numbering was made possible by the Na⁺³²S³⁴S^? species in natural abundance and from a 33% ³⁴S-enriched sample of S₂Cl₂. The spectroscopic constants ν₀₀ = 19 990 ± 10 cm^?, ω₀″ = 586 ± 2 cm^?1 and ω₀x₀″ = 2.8 ± 0.2 cm^?1 are in excellent agreement with those reported for S₂^? in alkali halide crystals at low temperature.     

Alkali metal ion-poly (ethylene oxide) complexes. II. Effect of cation on conductivity

Complexes of alkali metal salts with various polymers have for some time been recognized as fast ionic conductors. Polymer electrolyte fast ion conductors are currently under consideration for use in high energy density electrochemical cells. In order to aid in our understanding of the mechanism of ionic conductivity we have examined systematically complexes of poly(ethylene oxide) (PEO) with the alkali metal salt series of Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ with both tetraflouroborate (BF₄^-) and trifluoromethanesulfonate (CF₃SO₄^-) anions. The ratio of monomer to salt was 10:1 in all cases. Complex impedance measurements were made on all samples in the temperature range 40°–125°C. With CF₃SO₄^- as the anion a definite trend was apparent with the smallest cation Li⁺ being the worst conductor and Cs⁺, the largest cation, being the best. When BF₄^- salts are used, the Na⁺ complex is found to be the best conductor and Rb⁺ the worst. This study, in connection with our earlier studies, has shown that synergy between cation and anion in the polymer matrix is an important consideration in determining the ionic conductivity.     

Etudes electrique et Raman des verres du systeme B2O3 - Li2O - Li2SO4

New vitreous electrolytes with fast lithium ion carriers have been obtained in the B₂O₃ - Li₂O - Li₂SO₄ system. The variation of the ionic conductivity is discussed. Raman spectroscopy indicates that sulfate ions are diluted in the vitreous matrix without detectable interaction with the surrounding.     

Pool-Frenkel effect and high frequency dielectric constant determination of semiconducting P2O5-Li2MoO4-Li2O and P2O5-Na2MoO4-Na2O bulk glasses

The ternary 70P₂O₅-10Li₂MoO₄-20Li₂O and 70P₂O₅-10Na₂MoO₄-20Na₂O glasses, prepared by the press-melt quenching technique, were studied at temperatures between 298 and 418 K for their high dc electric field properties. For the above purpose, the effect of a strong electric field on the dc conduction of these amorphous bulk samples was investigated using the gap-type electrode configuration. At low electric fields, the current-voltage (I — V) characteristics have a linear shape, while at high electric fields (> 10³ V/cm), bulk samples show nonlinear effects (nonohmic conduction). Current-voltage curves show increasing departure from Ohm’s law with increasing current density, leading to critical phenomena at a maximum voltage (threshold voltage), known as switching (switch from a low-conduction state to a higher-conduction state at threshold voltage). The Pool-Frenkel high-field effect was observed at electrical fields of about 10³–10⁴ V/cm; then the lowering factor of the potential barrier, the high frequency dielectric constant, and the refractive index of these glasses were determined.