Influence of lithium phosphate concentration and temperature on the electrical conduction of (76V2O5-24P2O5)1−X (Li3PO4)X glasses

Characterization of the (76V₂O₅-24P₂O₅)_1−X (Li₃PO₅)_X, where X=0.0,0.01,0.02,0.10 and 0.15, glass has been done using X-ray diffraction and differential thermal analysis (DTA). The dc conductivity of the glass samples was studied over a temperature range from 300 to 593 K. The temperature dependence of dc conductivity shows two regions. One at relatively high temperature range, above θ_D/2, and the other at relatively low temperature range, below θ_D/2. The I-V characteristics of the glasses have been studied as a function of both temperature and Li₃PO₄ content. The I-V characteristics exhibits threshold switching with differential negative resistance. It's found that both the threshold voltage (V_th) and threshold current (I_th) are dependent on the temperature and lithium phosphate concentration.     

NMR relaxation of 7Li in concentrated lithium-ammonia solutions

The Knight shift and the spin-lattice relaxation time of ⁷Li in lithium-ammonia solutions have been measured at -57°C over the concentration range X_Li = 0.01–0.20 (X_Li: mole fraction of Li). The Knight shift increases with increasing metal concentration, while the relaxation rate, 1/T₁, shows a broad minimum around X_Li = 0.07.     

Conductivite ionique du lithium dans les solutions solides de structure boracite Li4+xB7O12+x/2X (X = Cl,Br) (0 ⩽ x ⩽ 1)

The study of the Li₄B₇O₁₂X-Li₂O (X = Cl, Br) systems at 750°C has made it possible to isolate Li_4+xB₇O_12+x/2X (0 ? x ? 1) solid solutions with boracite type structure. The evolution of electrical properties as a function of composition has been discussed in terms of structure and chemical bonding.     

The C1Πu-X1Σg+ fluorescence of Li2 excited by ultraviolet lines of an argon ion laser

The fluorescence spectra of ⁷Li₂ and ⁶Li₂ excited by an argon ion (3511 Å) laser are analyzed. No fluorescence was observed for 3514- or 3638-Å excitation or for ⁶Li⁷Li. For the C¹Π_u-X¹Σ_g⁺ electronic transition, the spectrum of ⁷Li₂ shows R and P doublets for 0 ≤ v″ ≤ 6 and that of ⁶Li₂ consists of Q lines for 0 ≤ v″ ≤ 11. Through the assignments of these lines (a) Hsu's (Ph.D. thesis, Fordham University, 1974, unpublished) molecular constants for C state have been verified, (b) the reliability of C- and X-state constants for ⁶Li₂ derived from those of ⁷Li₂ through mass-reduced scaling has been verified, and (c) the transition moment for the C-X transition of Li₂ has been shown by comparison of the observed and calculated intensities to be roughly independent of internuclear distance in the region near R_e for the C state.     

A1Σu+-X1Σg+ and B1Πu-X1Σg+ fluorescence of 6Li2 and 6Li7Li excited by a krypton ion laser

The A¹Σ_u⁺-X¹Σ_g⁺ and B¹Π_u-X¹Σ_g⁺ fluorescence of the ⁶Li₂ and ⁶Li⁷Li molecules has been studied for all krypton ion laser lines (468.0–799.3 nm) which might be expected to excite such fluorescence. Only two A-X fluorescence series of ⁶Li₂ were found (one excited by 647.1 nm, and one by 752.5 nm). No A-X fluorescence series of ⁶Li⁷Li was found. Five B-X fluorescence series of ⁶Li₂ were found (one each excited by 468.0, 476.2, and 530.9 nm, and two by 568.2 nm). Four B-X fluorescence series of ⁶Li⁷Li were found (one each excited by 468.0 and 482.5 nm and two by 520.8 nm). Calculated Einstein A coefficients and lifetimes for these transitions are also given.     

Structural and electrical properties of the α-form of metal-free phthalocyanine (α-H2Pc) semiconducting thin films

An X-ray structural study of thermally evaporated metal-free phthalocyanine thin films with various film thicknesses was performed. All samples studied had polycrystalline structure and the unit cell was found to be of the α-form. Variation of the deposition rate from 0.5 to 1 nm s⁻¹ had little effect on the structure. The films exhibit preferential orientation at low thickness; however, at higher thickness they become less orientated as additional peaks appear in the spectrum. The increase in the intensity of the first significant low angle peak with increasing thickness is attributed to the increased volume of the crystal probed during the X-ray exposure.The current density–voltage (J–V) characteristics of α-H₂Pc films sandwiched between two aluminum electrodes showed ohmic behavior at low voltages and space–charge-limited conduction (SCLC) at higher voltages. For comparison, similar measurements of the current density as a function of voltage were performed on zinc phthalocyanine, ZnPc, thin films using aluminum electrodes. The J–V characteristics showed ohmic behavior at low voltages followed by SCLC dominated by an exponential trap distribution at higher voltages. Consequently, in both H₂Pc and ZnPc films, aluminum electrodes act as if they are ohmic contacts. The implied provision of ohmic contacts using aluminum in this case is attributed to the formation of a thin Al₂O₃ layer during the deposition process.     

Precipitation of lamellar phases in H: LiNbO3 layers

Structural defects in a surface layer of the proton-exchanged waveguide layer formed on a substrate prepared from an X-cut lithium niobate single crystal are revealed and investigated using scanning electron microscopy and optical interference profilometry in combination with selective etching. It is established that these structural defects, which are oriented along the [0 15 1] crystallographic direction and matched to the matrix (the β phase of the H_xLi_{1 ? x} NbO₃ solid solution) through a network of misfit dislocations, consist of one of the H_xLi_{1 ? x} NbO₃ phases precipitated in the form of lamellar regions ～100 nm thick. Precipitation of lamellar phases precedes the destruction of the surface of the proton-exchanged layer. The presence of residual internal stresses in the LiNbO₃ initial crystal favors the formation of the lamellar phases.     

Mixed ion-polaron transport in lithium vanadium–molybdenum tellurite glasses

The electrical properties of mixed ion-polaron conducting vanadium tellurite glasses of the form XLi₂O·(1 − X)[0.5V₂O₅·0.5MoO₃]2TeO₂ have been studied by using the impedance spectroscopy in a wide range of temperature and composition. The obtained results confirm the existence of a transition from a typically electronic (polaronic) conductive regime when the molar fraction (X) of Li₂O is equal to 0, to an ionic conductive regime when X tends to 1. This transition is characterised by a deep minimum in the electrical conductivity of about 3 orders of magnitude. The correlated behaviour between conductivity and the mean distance between lithium ions and between vanadium ions reinforces the key idea of two independent migrating paths for both electrons and ions, respectively.     

Low voltage red phosphorescent organic light-emitting devices with triphenylphosphine oxide and 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl electron transport layers

We have developed red phosphorescent organic light-emitting devices operating at low voltages by using triphenylphosphine oxide (Ph₃PO) and 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) electron transport layers. 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) and tris-(1-phenylisoquinolinolato-C²,N) iridium(III) [Ir(piq)₃] were used as host and guest materials, respectively. Small voltage drops across the electron transport layers and direct injection of holes from 4,4′,4″-tris[N-(2-naphthyl)-N-phenyl-amino]-triphenylamine (2-TNATA) hole transport layer into the Ir(piq)₃ guests are responsible for the high current density at low voltage, resulting in a high luminance of 1000 cd/m² at low voltages of 2.8–3.0 V in devices with a structure of ITO/2-TNATA/CBP:Ir(piq)₃/DPVBi/Ph₃PO/LiF/Al.     

Electrochemical behavior of Li intercalation processes into a Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 cathode

Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO₂ structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂. Indeed, Li[Ni_0.50Mn_0.50]O₂ compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni_0.17Li_0.22Mn_0.61]O₂ and Li[Ni_0.25Li_0.17Mn₀.₅₈]O₂ compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni²⁺ and about Ni³⁺, while the oxidation state of Mn ion sustains Mn⁴⁺ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂, in which Ni ion changes between Ni²⁺ and NI⁴⁺. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process.     

Optical and electrical characterization of TiO2 nanotube arrays on titanium substrate

Novel oriented aligned TiO₂ nanotube (TN) arrays were fabricated by anodizing titanium foil in 0.5% HF electrolyte solution. It is indicated that the sizes of the TNs greatly depended on the applied voltages to some extent. The electrical properties of the TN arrays were characterized by current-voltage (I-V) measurements. It exhibits a nonlinear, asymmetric I-V characterization, which can be explained that there exists an n-type semiconductor/metal Schottky barrier diode between TN arrays and titanium substrate interface. The absorption edges shift towards shorter wavelengths with the decrease of the anodizing voltages, which is attributed to the quantum size effects. At room temperature, a novel wide PL band consisting of four overlapped peaks was observed in the photoluminescence (PL) measurements of the TN arrays. Such peaks were proposed to be resulted from the direct transition X₁ → X₂/X₁, indirect transition Γ₁ → X₂/X₁, self-trapped excitons and oxygen vacancies, respectively.     

Metastable phases in proton-exchanged waveguides on an X cut of lithium niobate

The formation and decomposition of high-temperature phases in proton-exchanged waveguide layers of H_xLi_{1 ? x} NbO₃ on an X cut of lithium niobate are studied using IR spectroscopy and x-ray diffraction. It is shown that the phase transitions that occur in the proton-exchanged layers between the high-temperature phases fixed by quenching from T = 200°C and the phase that is equilibrium at room temperature are accompanied by changes in the frequencies and integrated intensities of the spectral components of the absorption bands characterizing OH groups and hydrogen bonds in the crystal. These changes imply two paths of proton redistribution during these completely reversible phase transitions: (i) transfer of some protons from substitutional sites to interstitial sites and (ii) proton transfer between substitutional sites having different ionic environments. The phase transition from the phase that is equilibrium at room temperature into a high-temperature phase is found to be accompanied by a more than twofold increase in strain in the H_xLi_{1 ? x} NbO₃ layer lattice (x ≈ 0.50). The experimental data obtained confirm complete reversibility and the diffusionless character of these phase transitions.     

Characteristics of molybdenum oxide and chromium oxide cathodes in primary and secondary organic electrolyte lithium batteries I. Morphology,structure and their changes during discharge and cycling

Rechargeable positive electrodes for ambient temperature Li-batteries are mainly based on the same general principle: reversible topotactic Li⁺-intercalation into transition metal chalcogenide host lattices, yielding ternary phases Li_nMCh_x. After an intercalation/deintercalation cycle the original host lattice may be retained practically unchanged if the structure of the host matrix is determined by strong covalent bonds and if the concentration of intercalated ions was small. On the other hand, high concentration of unsolvated Li⁺ ions in fairly ionic oxide host lattices such as MoO₃, Cr₂O₅ or Cr₃O₈ (CrO_x) cause significant irreversible structural and also morphological changes of the host matrix. Moreover, ternary oxides Li_nMO_x prepared at room temperature are non-equilibrium phases — their structural parameters and transport properties vary with conditions of preparation, ageing time etc., and elevated temperature finally causes a complete and irreversible breakdown of their original structure. Prolonged cycling of crystalline large particle size MoO₃ leaves quasi-amorphous powders which, however, are still usable for rechargeable cathodes. Failure of Li_nMoO₃ and Li_nCrO_x electrodes is due to recrystallization via solution, forming e.g. Li₂MoO₄ from Li_nMoO₃. To obtain a better understanding of the limitations of MoO₃ and CrO_x cathodes under practical operation conditions changes in structure and morphology during electrochemical and chemical lithiation and after electrochemical cycling were followed by X-ray diffraction and SEM micrographs; supplementary results were obtained by electrochemical methods and by thermal analysis. Electronically conducting preparations of “hexagonal MoO₃” (which is a hydrated MoO₃ modification) were also characterized with respect to their discharge behaviour and reversibility in organic Li⁺-electrolytes ? their “sloping” discharge characteristics disqualify them for practical applications.     

Investigations of binary lithium-zinc,lithium-cadmium and lithium-lead alloys as negative electrodes in organic solvent-based electrolyte

The thermodynamic properties of the binary LiZn, LiCd and LiPb alloy systems were investigated in an organic solvent-based electrolyte at ambient temperature. Titration curves showed several intermediate phases existing in each lithium alloy system. There was a wide composition range in Li_yCd (1.5 ⩽ y ⩽ 3), which showed a very low equilibrium potential (below 60 mV) against pure lithium. There was a longer potential plateau in the LiPb system corresponding to Li_yPb (1 ⩽ y ⩽ 3) at about 450 mV against pure lithium. The preliminary charge-discharge and polarization results showed rather fast kinetics for Li_yZn (0.67 ⩽ y ⩽ 1), Li_yCd (1.5 < y < 2.0), and Li_yPb (1 < y < 3).     

Transport and equilibrium characteristics of γ-lithium vanadium bronze

The diffusion coefficient of Li⁺ in the γ-lithium vanadium bronze (Li_1+xV₃O₈) has been measured with the long-pulse galvanostatic technique. Values ranging from 1.7×10⁻⁷ cm²s⁻¹, at x=0.3, to 2.2×10⁻⁸ cm²s⁻¹, at x= 1.4, have been measured. The thermodynamic factors, d ln a/d ln c, determined from the OCV/x curve and from voltage relaxation after the current pulse, have a mean value of ∼15. The pseudo two-phase region observed in the OCV/x curve at high Li⁺ concentrations seems attributable to ordering of Li⁺ in specific sites and to alteration of the unit cell. This process is reversible as shown by X-ray diffractometry. Finally, from OCV/t plots at different x, the partial molar entropy of Li⁺ was determined. The values, on account of the large dE(x)/dt measured, are higher than those found for V₆O₁₃ or TiS₂.     

197Au Mössbauer effect studies on ternary alloys of gold with main-group metals

¹⁹⁷Au Mössbauer effect studies in the ternary gold alloys Li₂AuX (X = Ga, In, Tl; Ge, Sn, Pb; Bi) and Li₂Au_2?xIn_x (1.0 ? x ? 1.75), all of which crystallize in the cubic NaTl structure, have been performed at 4.2 K. The isomer shifts derived from the single-line spectra have been correlated with the average Allred-Rochow electronegativity of the first three coordination spheres around the gold atoms, normalized to the number of outer electrons and corrected for the distance from the gold atom. The isomer shifts have also been correlated with structural data from X-ray diffraction studies. Results of Dirac-Fock atomic structure calculations have been taken into account in discussing the possible valence electron configurations of gold. It is suggested that substantial 5d-6s mixing occurs with nearly matching charge compensation and additional 5d depletion through an interaction of the 5d band of gold with host orbitals of proper symmetry. A net charge flow off the gold sites appears in every case.     

Characteristics of molybdenum oxide and chromium oxide cathodes in primary and secondary organic electrolyte lithium batteries. Part II. Transport properties

Utilization and rate performance of metal chalcogenide host lattice cathodes depend on transport properties of phases Li_nMCh_x, i.e., on their electronic and Li⁺ conductivity. On the other hand, liquid phase Li⁺ diffusion in pores of the electrodes or rates of charge transfer and phase change reactions may also be limiting under certain conditions. For phases Li_nMO_x (M=Cr, Mo) and in particular for the model substance Li_nMoO₃ parameters controlling utilization and rate performance were followed during discharge and recharge, i,e., in dependence of composition and history. The main results can be summarized as below: Chemical diffusion coefficients D?_Li+in Li_nCrO_x and Li_nMoO₃ have their maxima close to n ca. 0.5 and drop sharply for n&#38;&#62;;1 - in the layered phase Li_nMoO₃, Li⁺ mobility is paralleled by the interplanar distance; D?_Li+ in discharged Li_nCrO_x and Li_nMoO₃ partly recovers during recharge, but never reaches the top values of the 1st discharge - this is related with irreversible structural disintegration of the host matrix; At the end of discharge (n ca. 1.5) a porous layer of a final discharge product is formed on Li_nCrO_x and Li_nMoO₃ particles. This layer is electronically insulating and Li⁺ transport through this layer is predominantly by liquid phase diffusion in the pores; The electrochemical intercalation of Li⁺ into Li_nCrO_x or Li_nMoO₃ is a 1st order reaction with respect to Li⁺ concentration in the electrolyte.     

Thermochemistry of the high and ambient temperature lithium vanadium bronze phases LixV2O5

The enthalpies of formation of a series of high and low temperature phases in the ternary oxide system Li_xV₂O₅ have been determined by solution calorimetry. Samples of the former, α-Li_0.04V₂O₅, β-Li_0.30V₂O₅, β'-Li_0.48V₂O₅ and γ-LiV₂O₅, were prepared by solid state reaction at 650°C. The ambient temperature materials Li_0.1V₂O₅(I), Li_0.45V₂O₅(II) and Li_1.03V₂O₅(III) were prepared by n-butyl lithiation in hexane. The thermochemistries of the two classes of material were examined and related to structural features and to the observed behaviour of V₂O₅ as a battery cathode material in lithium cells.     

Electronic structure and electrochemical properties of electrode material Li7−xMnN4

The electronic structure and the charge balance mechanism of the Li_7−xMnN₄ system were investigated by core-level electron energy loss spectroscopy. The spectra are strongly affected by configuration interactions and reveal the existence of a considerable amount of nitrogen 2p holes in the ground state. Based on the results, we conclude that the Li₇MnN₄ system can be classified into the charge transfer-type compounds. The systematic variation of the operating voltages versus Li/Li⁺ of the Li₇MnN₄ system and the other transition metal nitrides and oxides can be qualitatively explained by classification into the Mott–Hubbard and the charge transfer regimes.     

Low voltage electrodeposition of CNx films and study of the effect of the deposition voltage on bonding configurations

Carbon nitride (CN_x) films were deposited from acetonitrile at low voltage (150-450 V) through electrodeposition. The films were characterized by atomic force microscopy (AFM), Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. AFM investigations revealed that the grain size was ∼200 nm and roughness was ∼10 nm. The films were found to be continuous and close packed. IR spectra revealed existence of strong sp³, sp² type bonding and weak sp type carbon nitrogen bonds and these bonds were found to increase with voltage. The fraction of sp³-bonded species in the sample increased in low voltage range and after reaching maximum at 350 V, decreased for higher voltages. However, the concentration of sp² CN ring structures in the film increased with increasing voltage. Also, the peak width decreased at low voltages reaching a minimum and increased thereafter. It was observed that the voltage dependent increase in the concentration of polymeric type sp² CN (chain) structures was much more pronounced than that of graphitic type sp² CN (ring) structures. Raman spectra showed the presence of both the D and G bands. The shift in the G band indicated the presence of nitrogen in the film. The I_D/I_G ratio was found to increase with the incorporation of nitrogen. Auger electron spectroscopy (AES) showed a clear increase in the nitrogen content with increase in the voltage. The formation of the film could be explained on the basis of dissociation of electrolyte under applied voltage.