Electrochromic cells with iridium oxide display electrodes

We report the fabrication and electrochromic behavior of iridium oxide film electrodes, including a specific display electrode design compatible with the high peak ion-insertion current densities accepted by this material and necessary for the shortest possible response time. The configuration of a complete two-terminal display cell, in which the high capacity counter electrode behaves as a pseudo-reference electrode, is presented. Cell performance, including the use of IR compensated constant-voltage address when response time is limited by impedances external to the iridium oxide itself, is reported.     

Synthesis of praseodymium oxide nanofiber by electrospinning

Well-defined and uniform Pr₆O₁₁ nanofibers were synthesized by electrospinning of an aqueous sol-gel consisting of praseodymium nitrate hexa-hydrate and polyvinyl acetate. The synthesized Pr₆O₁₁ nanofibers mat was dried at 80 °C for 24 h under vacuum and finally annealed at 600 °C for 2 h in static air furnace. From crystalline properties, the synthesized Pr₆O₁₁ nanofibers XRD analysis revealed the typical cubic structure. The morphological observation showed that the synthesized Pr₆O₁₁ nanofibers composed of fibers length in several 100 nm and diameter of ∼20 nm. Similarly, transmission electron microscope (TEM) measurement revealed the good crystalline nature of the synthesized Pr₆O₁₁ nanofibers with the average diameter of ∼20 nm. Photoluminescence (PL) demonstrated a strong green-blue emission peak at 521 nm, suggesting that the Pr₆O₁₁ nanofiber exhibited good crystal quality with very less structural defects.     

Ionic conductivity of gadolinium-doped barium praseodymium oxide

To clarify the ionic conduction of Ba(Pr_0.6Gd_0.4)O_3−α, the electrical conductivity was measured in moist air and hydrogen atmospheres. The ionic transport number was estimated by a steam concentration cell, a hydrogen permeation cell, and a fuel cell. Temperature dependence of the conductivity in a moist air atmosphere differed from that in a moist H₂ atmosphere. The conductivity under reducing conditions increases with time according to the crystal structure change of Ba(Pr_0.6Gd_0.4)O_3−α due to oxygen loss in the lattice site. Under moist air conditions, the dominant conduction species in the Ba(Pr_0.6Gd_0.4)O_3−α electrolyte were mainly holes. However, the species changed into proton, oxide ion and hole by means of structure change in a reducing atmosphere. It was considered that the ionic conduction occurred due to the crystal structure change. It was predicted that this peculiarity of the conductivity of barium praseodymium oxide influenced the nonstoichiometric behaviour of Pr in the crystal structure.     

Investigations of a number of alternative negative electrode materials for use in lithium cells

There is a considerable interest in the replacement of graphite as the negative electrode reactant in rechargeable lithium batteries by composite electrodes containing alloys or convertible oxides. Some such materials can have much higher theoretical specific capacities than graphite, more than a factor of ten in some cases. In addition it would be desirable to eliminate the irreversible loss of capacity during the first charging cycle that is characterisitic of graphite electrodes, as well to raise the operating potential somewhat in order to reduce the danger of the formation of elemental lithium during recharging. The several strategies that have been followed in the search for attractive alternatives will be briefly described. It has been found to be difficult to obtain the desired combination of high capacity, low first cycle loss and capacity retention upon cycling. Investigations of the electrochemical behaviour of elemental boron and borides (B₄C, CaB₆, LaB₆, AlB₂, SiB₃), elemental silicon and silicides (Mg₂Si, FeSi₂, CoSi₂, NiSi₂, TiSi₂, VSi₂) and of siliconmonoxide, SiO, will be reported. The galvanostatic cycling method was used, with thick layer electrodes (30 μm) deposited upon copper foil in coffee bag-type cells with a liquid electrolyte. Lithium foil was used for the counter and reference electrodes. The results of the investigation of the morphological changes upon cycling, as observed by the use of SEM, will also be presented. Paper presented at the 7th Euroconference on Solid State Ionic, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Lattice dynamics of lithium oxide

Li₂O finds several important technological applications, as it is used in solid-state batteries, can be used as a blanket breeding material in nuclear fusion reactors, etc. Li₂O exhibits a fast ion phase, characterized by a thermally induced dynamic disorder in the anionic sub-lattice of Li⁺, at elevated temperatures around 1200 K. We have carried out lattice-dynamical calculations of Li₂O using a shell model in the quasi-harmonic approximation. The calculated phonon frequencies are in excellent agreement with the reported inelastic neutron scattering data. Thermal expansion, specific heat, elastic constants and equation of state have also been calculated which are in good agreement with the available experimental data.     

Pulsed laser deposition of praseodymium oxide films on silicon(100)

In this study, pulsed laser deposition (PLD) was used to deposit thin films of high-k dielectric praseodymium oxide on silicon(100). Photoluminescence spectroscopy (PL) shows the possibility of activating crystal defects in the Si substrate during the PLD process. Capacitance-Voltage (C–V) measurements yield an average dielectric constant of k=33 for Pr_xO_y films of different thicknesses. The leakage current is orders of magnitude lower than for SiO₂. PACS 77.55; 81.15.Fg     

Vacuum discharge from perovskite oxide electrodes

This paper presents results of the investigation of electrical discharge in vacuum from perovskite-like La_0.7Sr_0.3CoO₃ and YBa₂Cu ₃O_6.95 electrodes. Data are given on the local chemical composition of cathode surfaces subjected to nanosecond high-current arc discharges and on the erosion of ceramic cathode materials. The results of measurements of the work function and of the emission capability of extended ceramic cathodes and of field emission characteristics of clean surfaces of perovskite-like oxides are presented. A comparative analysis has been carried out of the behavior of ceramic cathodes with results obtained from the discharge of metallic electrodes     

Electrochemical study of molybdenum oxide film electrodes

Several different electrochemical techniques were used to study the redox reaction in an aqueous sulphuric acid solution at molybdenum oxide film electrode. It was determined by chronopotentiometry, along with cyclic voltammetry and impedance spectroscopy, that in the redox process, the H⁺ ion combines with an electron from the film to form an intermediate before entering the film, and that the transport of the H atom within the layer of oxide occurs purely by diffusion. The diffusion coefficient of the H atom was deduced from these data (D=10⁻¹² cm² s⁻¹).     

Ionic conductivity of electrolytes based on star-branched poly(ethylene oxide) with high concentration of lithium salts

Electrolytes based on star-branched poly(ethylene oxide) with lithium bis(trifluoromethanesulfone)imide LiTFSI and lithium iodide salts were prepared by casting from solution. The electrical properties of electrolytes subjected to various heating and cooling runs were studied by impedance spectroscopy and impedance spectroscopy simultaneous with optical microscope observation. Differential scanning calorimetry was used for additional characterization. The results indicate that in electrolytes with high content of salt, values of ionic conductivity comparable to that of dilute electrolytes can be achieved. Moreover, electrolytes with high amount of salt seem to show weaker temperature dependence of conductivity. Promising results in terms of ionic conductivity were obtained for mixture of LiTFSI and lithium iodide. A few problems which may decrease the performance of studied system as a solid electrolyte were also identified, from which changes of physical properties of samples subjected to thermal cycles and aging seem to be the most important ones.     

Magnetoelastic effects in praseodymium

The zero field single crystal elastic constants of praseodymium have been measured down to 4.2 K and agree with the work of Greiner et al. An applied magnetic field of 8 Tesla lowers C₆₆ by 0.3% at 4.2 K in contrast to an estimate of 15% lowering by Jensen.     

Alloy negative electrodes for lithium batteries formed in-situ from oxides

Fuji Photo Film Co. recently announced the development of lithium batteries employing oxide negative electrodes. Under near-equilibrium conditions these oxides are converted to lithium alloys during the first charging cycle. Thereafter, the properties should be essentially those of the resulting binary lithium alloys. The basic principles involved in the use of alloys as negative electrodes, as well as the conversion of oxides to alloys, are presented. Available data on the behavior of a number of lithium alloys and binary oxides as negative electrodes in lithium systems are also included. The lithiumtin system is discussed in some detail as it is a particularly relevant example. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Doped tin oxides as potential lithium ion battery negative electrodes

Recently some work has shown that tin oxide compounds can be promising anode materials in rechargeable lithium batteries. These materials show a higher capacity compared to the graphite that is used commercially. The present studies are focused on zinc doped tin oxides as anode materials, especially on the effect of ball-milling on the anode capacity. Different ratios of ZnO and SnO₂ with different times of ball-milling have been used as active materials. The inverse spinel, Zn₂SnO₄ has been prepared by both hand-grinding and ball-milling, followed by sintering and has also been investigated as an active material. Individual ball-milling of the oxides was observed to increase capacity, co-milling was fairly neutral and ball-milling before solid state reaction was observed to have a detrimental effect. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

Hybrid solar cells using nanorod zinc oxide electrodes and perylene monoimide–monoanhydride dyes

Hybrid solar cells have been fabricated using perylene monoimide–monoanhydride dyes with nanorod zinc oxide electrodes as electron transporting layers. We have investigated the influence of the spacer alkyl chain length of perylene monoimide–monoanhydride (PMIMA) dyes on the device performance in hybrid solar cells using nanorod zinc oxide electrodes. Nanorod zinc oxide electrodes with 50–150 nm of diameter were synthesized in the presence of PEG400 by using microwave heating method. We observed that the dyes with longer and brunched alkyl chains exhibit higher efficiencies in hybrid solar cells. We report the highest efficiency obtained with zinc oxide nanorods under standard conditions for perylene monoimide–monoanhydride derivative with PMIMA_1 that performs 400 mV open circuit voltage, 2.81 mA/cm² short-circuit current and 0.59% overall conversion efficiency.     

Intercalation electrodes in copper solid-state cells

The behaviour of transition-metal dichalcogenide intercalation electrodes in copper solid-state cells have been investigated by kinetic, diffusion and thermodynamic studies. The results indicate that the copper electro-intercalation process is reversible in the compounds examined, which are TiS₂ and NbS₂. The kinetics of the process are controlled by the diffusion of the electroactive species to and from the bulk of the electrode.     

Ultrasound assisted synthesis of nano-sized lithium cobalt oxide

Nano-sized HT-LiCoO(2) powders were prepared by sonochemical synthesis in an aqueous solution of lithium hydroxide containing cobalt hydroxide at approximately 80 degrees C without any further heat treatment at high temperature. The effects of the LiOH concentration, oxidation conditions, ultrasound irradiation time and temperature on the formation of the nano-sized HT-LiCoO(2) phase were investigated. The formation of the HT-LiCoO(2) phase was confirmed by X-ray diffraction and Raman spectroscopy. The TEM images showed the presence of HT-LiCoO(2) aggregates with a mean particle diameter of approximately 20 nm. The reaction mechanism of the ultrasound assisted synthesis of nano-sized LiCoO(2) was proposed on the basis of the XRD, X-ray absorption spectroscopy analysis and TEM observation of the reaction products taken during the course of the synthesis.     

Layered lithium chromium manganese oxide compounds for high capacity electrode materials in rechargeable lithium batteries

A series of Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ cathode materials were prepared by the sol-gel process. The structural characterization was carried out by fitting the XRD data by the Rietveld method. The results of X-ray diffraction show that the crystal structure is similar to that of thelayered lithium transition metal oxides (R3-m space group). The particle morphology and size were observed by SEM, and the elemental content was determined by ICP. The electrochemical performance of the cathode was evaluated in the voltage range of 2.0 ∼ 4.9 V with a current density of 7.947 mA/g. The Li_1.27Cr_0.2Mn_0.53O₂ electrode delivered a high reversible capacity of around 280 mAh/g in cycling. Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ was found to be a promising cathode material. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

Investigations of electron beam induced conductivity in silicon oxide thin films

Silicon oxide thin film conductivity under electron beam irradiation is studied. An induced current in the films is varied in a range from a few tenths to a few values of the beam current. The dependence of the current normalized to a product of the applied voltage and the beam current on the beam energy is found to have a maximum determined by the film thickness, beam energy, and sign of the applied voltage. For the negative voltage applied to the metal electrode deposited on the film, this maximum is observed at the beam energy, at which the depth generation function is smaller by several tens of nanometers than the film thickness. For the positive voltage on the metal electrode, the maximum is observed at higher beam energies. The obtained result could be qualitatively explained under the assumption that a stationary excess carrier distribution is formed under the electron beam. This distribution is shifted with respect to the generation function due to diffusion and drift of excess carriers. A value of this shift is of about a few tens of nanometers, and its sign indicates that the majority carriers providing the induced conductivity in the films studied are electrons.