The electric quadrupole interaction of 111Cd in ZrZn2 and Zn in the samples prepared at 8 GPa

The perturbed angular correlation (PAC) measurements with the ¹¹¹In-¹¹¹Cd nuclear probe embedded into the lattice of the cubic (C15) Laves compound ZrZn₂ showed that ¹¹¹Cd nuclei experienced an axially symmetric electric quadrupole interaction with a frequency ν _Q  = 132.4 MHz at room temperature. The samples were synthesized and doped with the probe at a pressure 8 GPa. The temperature dependence of ν _Q was shown to be linear: ν _Q (T) = 147(1 − 0.033 T) MHz. Since the value of ν _Q is very close to that known for ¹¹¹Cd in the lattice of Zn, we have checked if it could be assigned to residual Zn metal in the sample. For the Zn sample melted and doped with ¹¹¹In at 8 GPa we have obtained ν _Q  = 117.3 MHz at 300 K and 127 MHz at 80 K – both values considerably lower than that for ¹¹¹In doped Zn samples prepared at an ambient pressure. These data, and the fact that ν _Q (T) in Zn is known to follow the T ^3/2 law, allow to attribute the ν _Q value quoted above to ¹¹¹Cd nuclei at the substitutional sites with tetrahedral symmetry in the Zn sublattice of ZrZn₂.     

A novel approach to employ Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript> as anode active material for lithium batteries

In the present paper, we describe utilization of cathode active material as anode active material, for example, Li₂MnSiO₄. The lithium manganese silicate has been successfully synthesized by solid-state reaction method. The X-ray diffraction pattern confirms the orthorhombic structure with Pmn2 ₁ space group. The Li/Li₂MnSiO₄ cell delivered the initial discharge capacity of 420 mA h g⁻¹, which is 110 mA h g⁻¹ higher than graphitic anodes. The electrochemical reversibility and solid electrolyte interface formation of the Li₂MnSiO₄ electrode was emphasized by cyclic voltammetry.     

Electrochemical behavior of silicon compound in LiF–NaF–KF–Na<Subscript>2</Subscript>SiF<Subscript>6</Subscript> molten salt

The electrochemical reduction and nucleation process of Si⁴⁺ on an electrical steel electrode in the eutectic LiF–NaF–KF molten salt were investigated at 750 °C, by means of cyclic voltammetry and chronoamperometry technique. Silicon was electrodeposited on steel, and Fe₃Si was formed by the diffusivity of silicon on the electrode surface. The electrochemical reduction of Si⁴⁺ process in single-step charge transfer and the cathode process was reversible. The electrocrystallization process of silicon is controlled by progressive three-dimensional mechanism. The diffusion coefficient was calculated to be 5.42 × 10⁻⁷ cm²/s by chronopotentiometry at experimental conditions.     

Performance of palladium electrode for electrochemical hydrogen pump using strontium-zirconate-based proton conductors

An electrode design with no use of three-phase boundary was investigated using palladium electrode. The hydrogen evolution rate of the palladium electrode cell using SrZr_0.9Y_0.1O_3 − α electrolyte followed Faraday’s law up to 180 mA cm⁻², and the anode and cathode overpotentials were significantly lower than those of a platinum electrode cell, suggesting that the palladium electrode is effective to improve the performance of the hydrogen-pumping cell using SrZrO₃-based electrolyte. The rate-determining step (RDS) for electrode reaction was also investigated by changing the electrode morphology and hydrogen partial pressure, and it was suggested that the RDS of the anode is a reaction at electrode/electrolyte interface.     

Synthesis, structure characterization and magnetic properties of nanosize LiCo1 − y Ni y O2 prepared by sol–gel citric acid route

Single phase LiCo_1 − y Ni _y O₂ (y = 0.4 and 0.5) with fine particles and high homogeneity was synthesized by “chimie douce” assisted by citric acid as the polymeric agent and investigated as positive electrodes in rechargeable lithium batteries. The long-range and short-range structural properties are investigated with experiments including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and superconducting quantum interference device magnetometry. The physicochemical properties of the powders (crystallinity, lattice constants, grain size) have been investigated in this composition. The powders adopted the α-NaFeO₂ structure as it appeared from XRD and FTIR results. Magnetic measurements shows signal at low temperature attributed to the magnetic domains in the nanostructure sample from which we estimated that the cation mixing are 3.35 and 4.74% for y = 0.4 and 0.5 in LiCo_1 − y Ni _y O₂, respectively. LiCo_0.5Ni_0.5O₂ cathode yields capacity (135 mAh g⁻¹) compared to LiCo_0.6Ni_0.4O₂ cathode (147 mAh g⁻¹) when discharged to a cutoff voltage of 2.9 V vs. Li/Li⁺. Lower capacity loss and higher discharge efficiency percentage are observed for the cell of LiCo_0.6Ni_0.4O₂ cathode.     

An EIS study of La2 − x Sr x NiO4 + δ SOFC cathodes

La_2 − x Sr _x NiO_{4 +  δ} materials were investigated as cathodes for the electrochemical reduction of oxygen on a Ce_1.9Gd_0.1O_1.95 (CGO10) electrolyte using cone-shaped electrodes together with electrochemical impedance spectroscopy. The area-specific resistance (ASR) of the La_2 − x Sr _x NiO_{4 +  δ} nickelates towards the reduction of oxygen is equal to the ASR of perovskites; however, it is not as low as for the best Fe–Co-based perovskites. The lowest ASR is found for the compound La_1.75Sr_0.25NiO_{4 +  δ} with an ASR of 23.8 Ωcm² measured on a cone-shaped electrode in air at 600 °C. It is suggested that difference in oxide ionic conductivity of the nickelates is the main cause for the different activity of the nickelates towards the electrochemical reduction of oxygen.     

Cells studies on PEO/PEG/NaClO<Subscript>3</Subscript> thin-film electrolyte system based on composite V<Subscript>2</Subscript>O<Subscript>5</Subscript> electrode

The thin-film solid polymer electrolyte based on polyethylene oxide (PEO) with sodium chlorite (NaClO₃) has been prepared by a solution-cast technique. The electrolyte was characterized by X-ray diffraction (XRD), infrared (IR), cyclic voltammetry, alternating current conductivity, and Wagner’s polarization studies. The complexation of NaClO₃ with PEO was confirmed through the XRD and IR studies. The transference number measurement has shown that the ion transport is predominant over electrons in the polymer electrolytes (t _ions ≈ 0.94). The conductivity enhancement was observed in the case of the PEO/NaClO₃ system with the addition of plasticizers (low-molecular-weight polyethylene glycol, organic solvents propylene carbonate and dimethyl formamide. Cyclic voltammetry analysis showed the stability and redox character of the electrolyte and electrode. Finally, polymer electrolyte systems were examined by electrochemical cell studies using V₂O₅ and composite V₂O₅ cathode at temperature of 35 °C. Overall, the plasticized electrolyte shows a better electrochemical performance, and a higher discharge capacity was observed in composite V₂O₅-based cells over V₂O₅-based cells.     

Electrochemical cell with two layers cathode for NO decomposition

An electrochemical cell composed of an yttria-stabilized zirconia disk and two layers cathode was used for nitrogen monoxide decomposition. It was found that covering the Pt cathode by a mixture of oxygen ionic conductor (YSZ) and electronic conductor (NiO) leads to enhancement of the performance of the electrochemical cell for NO_x decomposition in the presence of excess oxygen. The decomposition activity was measured for the one-compartment cell oxide|(cathode)|YSZ|(anode) by applying a DC voltage lower than 3.7 V in the temperature range 550–700 °C. The microstructure of the YSZ-NiO mixed oxide electrodes was investigated in dependence of the cell operating condition and the working electrode sintering temperature. The correlation between the microstructure of the mixed oxide electrode and conversion rate of NO was studied. The phenomenon of self-optimization of the microstructure of the NiO-YSZ working electrode during the cell operation was observed and investigated. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Line strength and collisional broadening studies of hydrogen sulphide in the 1.58 μm region using diode laser spectroscopy

High resolution diode laser spectroscopy has been applied to the detection of hydrogen sulphide at ppm levels utilizing different transitions within the region of the ν ₁+ν ₂+ν ₃ and 2ν ₁+ν ₂ combination bands around 1.58 μm. Suitable lines in this spectral region have been identified, and absolute absorption cross sections have been determined through single-pass absorption spectroscopy and confirmed in the Doppler linewidth regime using cavity enhanced absorption spectroscopy (CEAS). The desire for a sensitive system potentially applicable to H₂S sensing at atmospheric pressure has led to an investigation on suitable transitions using wavelength modulation spectroscopy (WMS). The set-up sensitivity has been calculated as 1.73×10⁻⁸ cm⁻¹ s^1/2, and probing the strongest line at 1576.29 nm a minimum detectable concentration of 700 ppb under atmospheric conditions has been achieved. Furthermore, pressure broadening coefficients for a variety of buffer gasses have been measured and correlated to the intermolecular potentials governing the collision process; the H₂S–H₂S dimer well depth is estimated to be 7.06±0.09 kJ mol⁻¹.     

On the flavor composition of the solar <Superscript>7</Superscript>Be neutrino

The flavor composition of the solar beryllium neutrino was analyzed using schemes that include the new (heavy) neutrino (ν₄) at a negligible angle of mixing with the light partners ν _e , ν_μ, and ν_τ.     

Enhanced cyclability of triple-metal-doped LiMn2O4 spinel as the cathode material for rechargeable lithium batteries

To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4-V-class lithium secondary batteries, spinel phases LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) were successfully prepared using the sol–gel method. The spinel materials were characterized by powder X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Electrochemical studies were carried out using the Li|LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn₂O₄ spinel electrode in spite of a small reduction in the initial capacity. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.     

Electrochemical cell performance studies on all-solid-state battery using nano-composite polymer electrolyte membrane

All-solid-state proton-conducting polymeric batteries have been fabricated in the cell configurations: Zn + ZnSO₄·7H₂O (anode) || polyethylene oxide (PEO):NH₄HSO₄ + SiO₂ || MnO₂ + C (cathode) and Zn + ZnSO₄·7H₂O (anode) || PEO:NH₄HSO₄ + SiO₂ || PbO₂ + V₂O₅ + C (cathode). Nano-composite proton-conducting polymeric membrane in wt.% composition, 92PEO: 8 NH₄HSO₄ + 3 SiO₂, synthesized by solution cast technique, has been used as electrolyte. Dispersal of nanosized (8 nm) fumed-SiO₂ particles resulted into an enhancement in the room temperature conductivity of polymer electrolyte host, 92PEO: 8 NH₄HSO₄ (wt.%), approximately by an order of magnitude with the substantial increase in the mechanical strength of the films. Details on the electrolyte film casting and ion transport characterization studies have been discussed elsewhere in the literature. However, a brief mention has been made for reference. An open circuit voltage in the range 1.5–1.8 V, obtained for both the batteries, is in very good agreement with the value reported. The cell performance has been studied under varying load conditions. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

AC conductivity and relaxation behavior in ion conducting polymer nanocomposite

We report the ac conductivity and relaxation behavior analysis for a heterogeneous polymer–clay nanocomposite (PNC) having composition (polyacrylonitrile)₈LiCF₃SO₃ + x wt.% dodecylamine modified montmorillonite. Charge transport behavior in an ionically conducting PNC has been analyzed systematically and correlated with the macroscopic parameters like polymer glass transition temperature and available free mobile charge carriers. Intercalation of cation coordinated polymer into the nanometric clay channels has been confirmed by high-resolution transmission electron microscopy. The electrical properties of the intercalated PNC films have been studied using complex impedance/admittance spectroscopy. Excellent correlation of relaxation behavior with polymer glass transition temperature (T _g) confirmed the objectives of the work. An analysis of dielectric relaxation indicates that PNC films are lossy when compared with polymer–salt film. This result is a direct outcome of faster ion dynamics leading to strong electrode polarization effect due to the accumulation of charge carriers at the interface.     

Elastic properties of TeO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Ag<Subscript>2</Subscript>O glasses

A series of glasses [(TeO₂) _x (B₂O₃)_1−x ]_1−y [Ag₂O] _y with x = 70 and y = 10, 15, 20, 25 and 30 mol% were synthesised by rapid quenching. Longitudinal and shear ultrasonic velocity were measured at room temperature and at 5 MHz frequency. Elastic properties, Poisson's ratio, microhardness, softening temperature and Debye temperature have been calculated from the measured density and ultrasonic velocity at room temperature. The experimental results indicate that the elastic constants depend upon the composition of the glasses and the role of the Ag₂O inside the glass network is discussed. Estimated parameters based on Makishima–Mackenzie theory and bond compression model were calculated in order to analyse the experimental elastic moduli. Comparison between the experimental elastic moduli data obtained in the study and the calculated theoretically by the mentioned above models has been discussed.     

Co-precipitation synthesis and performance of multi-doped LiCrxNixMn2-2xO4-zFz cathode materials for lithium ion batteries

Multiple ion-doped lithium manganese oxides LiCr_xNi_xMn_2-2xO_4-zF_z (0 < x ≤ 0.25, z =  0.05, 0.1) with a spinel structure and space group Fd m were prepared by using the co-precipitation procedure carried out in water–alcohol solvent using adipic acid as the chelating agent. The electrochemical measurements indicated that the charge/discharge capacities of the samples prepared at 600 °C are higher than that of the treatment at 800 °C or microwave heating. The capacitance-voltage (CV) curves of LiCr_xNi_xMn_2-2xO_4-zF_z (0 < x ≤ 0.25, z = 0.05, 0.1) showed that when x ≤ 0.1, the samples had two reduction–oxidation peaks at 4.0 to 4.2-V region, whereas when x > 0.1, the samples had only one reduction–oxidation peak at 4.0- to 4.2-V region in CV measurements and could offer more stable voltage plateau in a 4-V region and also had stable electrical conductivity after 20 cycles. Another reduction–oxidation peak appeared in 4.6-4.8-V region (Ni²⁺–Ni⁴⁺ reduction–oxidation peaks); this suggests that the LiCr_xNi_xMn_2-2xO_4-zF_z (0.1 < x≤ 0.25, z = 0.05, 0.1) cathode material could offer 4.6 to 4.8-V charge/discharge plateaus, and its specific capacity increases with increasing Ni²⁺. The impedance measurements of the cell proved that the F⁻ anion doped can not only prevent Mn³⁺ from disproportion but also can prevent the passivation film from forming and can help keep stable the cell’s electrical properties. The LiCr_0.05Ni_0.05Mn_1.9O_3.9F_0.1 sintered at 600 °C shows the best cycle performance and the largest capacity in all prepared samples; its first discharge capacity is 120 mAh/g, and the discharge capacity loses only 1.78% after 20 cycles. After 100 cycles, it still remains in the spinel structure.     

AC Conductivity,XRD and transport properties of melt quenched PbI<Subscript>2</Subscript>–Ag<Subscript>2</Subscript>O–Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Composite materials used for electrode and electrolyte materials have been intensely studied in view of their advantages such as higher conductivity and better operational performance compared to their single-phase counterparts. The present work aims at studying the electrical and structural characteristics of a new composite electrolyte namely, (PbI₂) _x  − (Ag₂O–Cr₂O₃)_100−x where x = 5, 10, 15, 20, and 25 mol%, respectively, prepared by the melt quenching technique. The room temperature X-ray diffraction spectra revealed certain crystalline phases in the samples. AC conductivity analysis for all the prepared samples was carried out over the frequency range 1 MHz–20 Hz and in the temperature window 297–468 K. The room temperature conductivity values were calculated to be in the order of 10⁻⁵–10⁻³ Scm⁻¹. An Arrhenius dependence of temperature with conductivity was observed, and the activation energies calculated were found to be in the range 0.27–0.31 eV. Furthermore, the total ionic transport number (t _i) values obtained for all these indicated the ionic nature of this system. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Solid polymer electrolytes based on squaric acid structure

Poly(squarate)s (PPS-1 and PPS-2) were synthesized by the reaction of squaryl dichloride with hydroquinone for PPS-1 and with 2,5-diethoxy-1,4-bis(trimethylsilyloxy)benzene for PPS-2, and the ionic conductivities, thermal properties, and electrochemical and thermal properties of their polymer electrolytes with LiN(CF₃SO₂)₂ were investigated. The ionic conductivity increased with increasing the lithium salt concentration for the PPS-1–LiN(CF₃SO₂)₂ electrolyte, and the highest ionic conductivities of 8.60 × 10⁻⁵ S/cm at 100 °C and 9.57 × 10⁻⁸ S/cm at 30 °C were found at the [Li] to [O] ratio of 2:1. And also, the ionic conductivity for the PPS-1–LiN(CF₃SO₂)₂ electrolyte increased with an increase in the lithium salt concentration, reached a maximum value at the [Li] to [O] ratio of 1:2, and then decreased. The highest ionic conductivity was to be 1.04 × 10⁻⁵ S/cm at 100 °C and 1.71 × 10⁻⁸ S/cm at 30 °C, respectively. Both polymer electrolytes exhibited relatively better electrochemical and thermal stabilities. Addition of the PPS-1 as a plasticizer into the poly(ethylene oxide) (PEO)–LiN(CF₃SO₂)₂ electrolyte system suppressed the crystallization of PEO, and improved the ionic conductivity at room temperature. Invited paper dedicated to Professor W. Weppner on his 65th birthday.     

ECTDL study of N 2 - and O 2 -pressure broadening of a series of ammonia lines in the 1.5 μm (ν 1 +ν 3 ) combination band

Nitrogen and oxygen pressure broadening parameters for seven ^r P(J”,0) transitions of the ν₁+ν₃ overtone band of the main isotope of ammonia with J” varied from 2 to 9 have been measured at room temperature using an external cavity tunable diode laser spectrometer. Air-broadening parameters have also been calculated from the N₂ and O₂ measurements. The results are compared to previous measurements in the ν₁, ν₂, ν₃, ν₄ and ν₁+ν₃ bands and to the parameters for the ν₃ band that are reported in the HITRAN database. PACS 33.70.Jg; 33.70.-W; 33.20.Ea; 42.62.Fi; 42.68.Ca     

Characterisation of Ba2In2 − x Sn x O5 + x/2 oxide ion conductors

The Ba₂In_2 − x Sn _x O_5 + x/2 solid solution was confirmed up to x = 1 by solid-state reaction. X-ray diffraction at room and at elevated temperatures, Raman scattering and impedance spectroscopy were used to characterise the samples. The structure refinement of the composition x = 0.1 from neutron diffraction data reveals that tin is preferentially located in the tetrahedral layers of the brownmillerite. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007