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Transition metal oxides with ramsdellite and spinel structures have been the subject of considerable investigation as candidate electrode materials for lithium-ion batteries. Good ionic conductivity has been reported for the ramsdellite Li{sub 2}Ti{sub 3}O{sub 7}, and the spinel Li{sub 4}Ti{sub 5}O{sub 12} has been shown to exhibit good electrochemical properties as a Li-anode material. The authors have recently demonstrated that ramsdellite series Li{sub 1+x}Ti{sub 2{minus}2x}O{sub 4} displays a complete range of solubility at high temperatures between compositions LiTi{sub 2}O{sub 4} and Li{sub 2}Ti{sub 3}O{sub 7} and that these phases can be preserved to room temperature by quenching. In this study they report on the electrochemical properties of members of this series of ramsdellite phases and the ramsdellite form of TiO{sub 2}. Comparison is made with the electrochemical properties of the spinel phase Li{sub 4}Ti{sub 5}O{sub 12}. In cyclic voltammetry, spinel Li{sub 4}Ti{sub 5}O{sub 12} showed a major, reversible peak at about 1.55 V vs. Li. The ramsdellite phases showed a similar reversible peak at just less than {minus}1.5 V; however, a number of additional reversible peaks were observed at up to 2.0 V. As the x value in Li{sub 1+x}Ti{sub 2{minus}2x}O{sub 4} increased, these extra peaks moved to smaller potentials,more » and they were observed to merge with the 1.5 V peak for Li{sub 2}Ti{sub 3}O{sub 7}. The presence of these extra peaks is thought to reflect the availability of additional sites in the ramsdellites. On charging and discharging, the potential was in the range from 1.5 to 2.5 V, although the behavior was not as flat as for the spinel. High capacities were observed, typically approaching 200 mAh/g. Initial cycling efficiencies were generally on the order of 80--90%, although no attempt has yet been made to optimize morphology. On cycling TiO{sub 2} ramsdellite, capacity generally faded from an initial value of 300 mAh g{sup {minus}1} to a stable capacity of 190 mAh g{sup {minus}1} by cycle ten.« less

Monte Carlo techniques are used to simulate the thermodynamics and diffusion of Li in the intercalation compound Li{sub y}Mn{sub 2}O{sub 4}. Results are presented for stoichiometric Li{sub y}Mn{sub 2}O{sub 4} and for Li-rich Li{sub y}Mn{sub 2}O{sub 4} containing pinned Li. The predicted theoretical open circuit potential compares favorably with literature results. The influence of Li-Li interactions on the activation energy leads to a diffusion coefficient that depends upon concentration. The diffusion coefficient is interpreted in terms of a thermodynamic factor and a binary interaction parameter.

Li{sub x}Mn{sub 2}O{sub 4} spinel normally undergoes a transformation from its cubic to tetragonal phase when x exceeds 1 due to a collective Jahn-Teller distortion, resulting in poor cyclability when both the 4 and 3 V intercalation plateaus are utilized. In this study, the authors show that this transformation is suppressed in spinels of composition up to x {approx} 2 obtained through the electrochemical cycling of orthorhombic LiMnO{sub 2}. X-ray diffraction, transmission electron microscopy, and high-resolution electron microscopy studies together show the cycling produces a cubic spinel containing partial tetrahedral cation site occupancy and a nanodomain structure (20 to 50 nm size) within parent single-crystalline oxide particles. This structure is responsible for the cycling stability of electrochemically produced spinel. The reversible capacity (272 mAh/g) and energy density (853 Wh/kg) achieved at a low charge-discharge rate (3.33 mA/g) in the present samples are the highest among crystalline LiMnO{sub 2} materials reported to date.

Thin-film cathodes of lithium manganese oxide, 0.3--3 {micro}m thick, were deposited by rf magnetron sputtering of a LiMn{sub 2}O{sub 4} ceramic target onto unheated substrates. The resulting films were dense, {approximately}4.2 g/cm{sup 3}, with a {approximately}50 {angstrom} nanocrystalline spinel structure. The film composition was typically Li{sub x}Mn{sub 2{minus}y}O{sub 4} with y {approximately} 0.3 and 1.2 < x < 2.2. When cycled in a thin-film rechargeable lithium battery, specific cathode capacities of 145 {+-} 23 and {approximately}270 mAh/g were realized for discharge from 4.5 V to either 2.5 or 1.5 V, respectively. The discharge and charge current densities were limited by the resistivity of lithium transport into and through the cathode. After thousands of cycles at 25 C, there was a small increase in cell resistance. After several hundred cycles at 100 C, the discharge curves developed a stable knee at {approximately}4 V characteristic of crystalline LiMn{sub 2}O{sub 4} cathodes. The polarization of the discharge/charge cycles were interpreted in terms of free energy of mixing curves.

The standard Gibbs energies of formation of IrO2, CaIrO3, Ca2IrO4 and Ca4IrO6 have been measured in the temperature range 940-1350 K using solid-state cells with (Y2O3) ZrO2 as the electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode. For the design of appropriate working electrodes, phase relations in the ternary system Ca-Ir-O were investigated at 1300 K. The only stable oxide detected along the binary Ir-O was IrO2. Three ternary oxides. CaIrO3, Ca2IrO4, and Ca4IrO6, compositions of which fall on the join CaO-IrO2, were found to be stable. Each of the oxides coexisted with pure metal Ir. Therefore, five working electrodes were prepared, consisting of mixtures of Ir + IrO2, Ir + IrO2 + CaIrO3, Ir + CaIrO3 + Ca2IrO4, Ir + Ca2IrO4 + Ca4IrO6, and Ir + Ca4IrO6 + CaO. These mixtures unambiguously define unique oxygen chemical potentials under isothermal and isobaric conditions. A novel apparatus, incorporating a buffer electrode between reference and working electrodes to absorb the electrochemical flux of oxygen through the solid electrolyte, was used for measurement. The buffer electrode prevented polarization of the measuring electrode and ensured accurate data. The standard Gibbs energies of formation of the compounds, obtained from the emf of the cells, can be represented by the equations IrO2ΔfG°/J mol-1 = -239, 230 + 172.19T (±240) CaIrO3Δf(ox)G°/J mol-1 = -29, 460 + 1.39T (±380) Ca2IrO4Δf(ox)G°/J mol-1 = -35, 145 + 0.81T (±410) Ca4IrO6Δf(ox)G°/J mol-1 = -37, 400 + 2.01T (±630) where Δf(ox)G° represents the standard Gibbs energy of formation of the ternary compound from its component binary oxides CaO and IrO2. Based on the thermodynamic information, chemical potential diagrams for the system Ca-Ir-O were developed.

In this study, oxide ion conduction characteristics of doubly doped PrGaO{sub 3} were investigated. It is found that PrGaO{sub 3} doped with Sr (or Ca) for the Pr site and Mg for the Ga site exhibits the high oxide ion conduction which was slightly less than that measured for doubly doped La(Sr)Ga(Mg)O{sub 3} (LSGM). Doping alkaline earth cations for the Pr site and Mg for the Ga site of the PrGaO{sub 3} increased its oxide ion conductivity. For temperatures above 1073 K, the highest oxide ion conductivity was obtained for the composition of Pr{sub 0.93}Sr{sub 0.07}Ga{sub 0.85}Mg{sub 0.15}O{sub 3} (PSGM). On the other hand, the apparent activation energy of Pr{sub 0.93}Ca{sub 0.07}Ga{sub 0.85}Mg{sub 0.15}O{sub 3} (PCGM) was as low as 0.65 eV. Therefore, the electrical conductivity of PCGM was higher than that of LSGM at temperatures below 873 K. Although hole conduction was observed, electron conductivity of the doubly doped PrGaO{sub 3} was almost independent of the oxygen partial pressure from p{sub O{sub 2}} = 1 to 10{sup {minus}21} atm. It is clear that doped PrGaO{sub 3} is a new fast oxide ion conductor over a wide range of oxygen partial pressures. On the other hand, a nonlinearity was observedmore » on the Arrhenius plot of electrical conductivity for Ca-doped PrGaO{sub 3} and the high temperature X-ray diffraction (XRD) measurement suggested that it was due to phase transition from orthorhombic to rhombohedral or tetragonal, which may decrease the mobility of oxide ions. Application of PSGM and PCGM for an electrolyte of solid oxide fuel cell was also investigated in order to cross-check the findings of the fast oxide ion conductivity. This study revealed that PSGM and PCGM were a new family of fast oxide ion conductors.« less

The dissolution behavior of La{sub 2}Cu{sub 4} has been examined by electrochemical techniques in aqueous media under open-circuit conditions at 298 K. La{sub 2}CuO{sub 4} is dissolved by aqueous acid at proton-mass transport limited rates in 1 M NaCl. Rotating ring-disk electrode (RRDE) techniques were employed in collection (product detection) and shielding (reactant removal) measure modes to monitor the surface chemistry, including a new approach not involving separate disk electrode H{sup +} reduction measurements as required heretofore. Related techniques monitoring the competitive oxygen evolution reaction were used to study the coulometric efficiency of anodic formation of the superconductor phases, La{sub 2}CuO{sub 4+x}, in alkaline medium. Solid-state diffusion severely limits growth.

The electroanalytical behavior of thin electrodes is elucidated by the simultaneous application of three electroanalytical techniques: slow‐scan‐rate cyclic voltammetry (SSCV), potentiostatic intermittent titration technique, and electrochemical impedance spectroscopy. The data were treated within the framework of a simple model expressed by a Frumkin‐type sorption isotherm. The experimental SSCV curves were well described by an equation combining such an isotherm with the Butler‐Volmer equation for slow interfacial Li‐ion transfer. The apparent attraction constant was −4.2, which is characteristic of a quasi‐equilibrium, first‐order phase transition. Impedance spectra reflected a process with the following steps: ion migration in solution, ion migration through surface films, strongly potential‐dependent charge‐transfer resistance, solid‐state diffusion, and accumulation of the intercalants into the host materials. An excellent fit was found between these spectra and an equivalent circuit, including a Voigt‐type analog ( migration through multilayer surface films and charge transfer) in series with a finite‐length Warburg‐type element ( solid‐state diffusion), and a capacitor (Li accumulation). In this paper, we compare the solid‐state diffusion time constants and the differential intercalation capacities obtained by the three electroanalytical techniques. © 1999 The Electrochemical Society. All rights reserved.

To get insight into the selective etching of In 0.53 Ga 0.47 As and In 0.72 Ga 0.28 As 0.61 P 0.39 with respect to InP in alkaline K 3 Fe(CN) 6 -containing solutions, the electrochemical and etching properties of In 0.53 Ga 0.47 As and In 0.72 Ga 0.28 As 0.61 P 0.39 were studied by rotating (ring)-disk voltammetry and by electrical impedance and etch rate measurements. It is shown that both In 0.53 Ga 0.47 As and In 0.72 Ga 0.28 As 0.61 P 0.39 are etched by K 3 Fe(CN) 6 in an electroless etching process, in which holes are injected by K 3 Fe(CN) 6 and consumed in the anodic dissolution. The observed selectivity in the etching of In 0.53 Ga 0.47 As and In 0.72 Ga 0.28 As 0.61 P 0.39 vs. InP is due to a difference in valence band-edge position, which determines the hole injection rate. Furthermore, it was found that a mechanism of galvanic element formation enhances the selectivity when InP and In 0.53 Ga 0.47 As or InP and In 0.72 Ga 0.28 As 0.61 P 0.39 are in electrical contact.

Li{sub 1.33}Ti{sub 1.6}7O{sub 4} synthesized from Li{sub 2}CO{sub 3} and TiO{sub 2} was electrochemically inserted with lithium at room temperature. The defect spinel Li{sub 1.33}Ti{sub 1.67}O{sub 4} and the fully lithiated Li{sub 2.33}Ti{sub 1.67}O{sub 4} with ordered rock-salt-type structure show nearly identical X-ray diffractions. Due to similar lattice constants of both phases and the low scattering factor of the lithium ions, the identification of the insertion mechanism using X-ray powder diffraction is possible only by using high angle X-ray scans of several samples inserted with different amounts of lithium. Precise analysis of the obtained data supplies the evidence for the presence of two distinct phases which are mutually interconvertible upon lithium exchange. This result is in good agreement with electrochemical data postulating a two-phase mechanism from the constant electrical potential found during cycling.

Copper indium diselenide (CIS) is electrodeposited in a single step on chemical bath deposited cadmium sulfide layers in order to form a superstrate cell structure. The influence of the electrodeposition potential on junction formation is studied by solid-state photocurrent voltage and photocurrent spectral responses. Secondary ion mass spectroscopy depth profiling shows that cadmium and sulfur diffusion from the CdS layer into the CIS layer is small up to annealing temperatures of 320 C. The diffusion process is found to be related to the composition of the CIS film, which in turn is determined by the electrodeposition potential. Interdiffusion processes are hindered in indium-rich CIS films. A preliminary CIS superstrate cell characteristic is presented yielding an efficiency of 1.5%.

Calcium-substituted lanthanum chromites were synthesized using a mixed lanthanide precursor composed primarily of La, Nd, Ce, and Pr. The thermal and electrical properties of these materials were measured and compared to similar chromites synthesized with lanthanum nitrate. The presence of Nd and Pr in the chromite resulted in a lowering of the thermal expansion coefficient and an increase in the temperature necessary to attain full density. Arrhenius plots of electrical conductivity were nonlinear with an inflection at temperatures between 625 and 750 C, indicating an increase in the carrier concentration with temperature. The increase in carrier concentration was consistent with the reduction of Ce{sup 4+} to ce{sup 3+}, resulting in a corresponding increase in Cr{sup 4+} in order to preserve electrical neutrality. The presence of both tri- and tetravalent Ce was substantiated using dilatometry measurements and X-ray photoelectron spectroscopy. The mixed lanthanide precursor is a possible low cost alternative for the synthesis of rare earth chromites for applications such as interconnects in solid oxide fuel cells.

The introduction of plasma damage in InGaP/GaAs and AlGaAs/GaAs high electron mobility transistors (HEMTs) has been investigated using both inductively coupled plasma and electron cyclotron resonance Ar discharges. The saturated drain-source current is found to be decreased through introduction of compensating deep levels into the InGaP or AlGaAs donor layer. The degradation of device performance is a strong function of ion energy and ion flux, and an advantage of both high density plasma tools is that ion energy can be reduced by increasing the plasma density. Increasing process pressure and source power, and decreasing radio-frequency chuck power produce the lowest amounts of plasma damage in HEMTs.

The effectiveness of fluorine incorporation control for reliability improvement of the AlInAs/GaInAs high electron mobility transistor (HEMT) is demonstrated. The inverted-type HEMT (i-HEMT) is found to be one of the feasible structures. In this structure, the GaInAs channel layer functions as a blocking layer against the thermal diffusion of fluorine into the AlInAs electron supply layer, which is a main cause of the electrical deterioration in the HEMT material. Under dc operation at an ambient temperature of 170°C, the zero-gate-bias saturated drain current of the i-HEMT decreases only a few percent even after 3,500 h. The projected median-time-to-failure of the i-HEMT is estimated to be 10 7 h at a temperature of 125°C, which is almost twice that of the conventional-type AlInAs/GaInAs HEMT.

Doped and undoped Mn spinels have been evaluated at 55°C in terms of capacity losses upon cycling and storage. The influence of such factors as doping, electrolyte nature, voltage range and constant- or floating-potential storage have been evaluated. Spinels of composition Li 1.02 M 0.05 Mn 1.95 O 4 (M = Ga or Cr) exhibit fade rates of 0.15 to 0.20 mAh/g cycle vs. 0.28 mAh/g cycle for the undoped spinel. This reduction may still be unsatisfactory from a practical standpoint, but it is enhanced by two different approaches: (i) storing a cell for some days at 55°C in, e.g., LiBF 4 -EC/PC; (ii) making a double substitution in the spinel, e.g., with Ga and Cr. The first approach brings the fade rate to 0.07 mAh/g cycle for both Ga-doped (2.5 mol %) and undoped spinel, whereas the second one allows a reduction to 0.05 mAh/g cycle, that is less than 0.05%/cycle. These rates of capacity loss are the lowest reported thus far at 55°C. By properly tuning the Li, Ga, and Cr content of the spinel, it seems possible to have simultaneously good average capacities (∼110 mAh/g in 100 cycles) and limited fade rates at 55°C.

Thin films of antimony sulfide have been deposited from chemical baths containing antimony trichloride and sodium thiosulfate maintained at 10 C. Upon annealing in nitrogen at 300 C for 1 h, the films become photosensitive with photo- to dark-current ratio of two to three orders of magnitude at 2 kW/m{sup 2} tungsten halogen radiation. The annealed films are crystalline with an X-ray diffraction pattern matching that of stibnite, Sb{sub 2}S{sub 3}, (JCPDS 6-0474) and show an optical bandgap of 1.78 eV. Deposition of a thin film of CuS on the antimony sulfide thin film and subsequent annealing in nitrogen at 250 C for 1 h produces films with acceptable solar control characteristics: integrated visible transmittance, T{sub vis}, 15%; integrated visible reflectance, R{sub vis}, 12%; integrated infrared transmittance, T{sub ir}, 14%; integrated infrared reflectance, R{sub ir}, 36%; and a shading coefficient of about 0.35. The X-ray diffraction patterns of the annealed Sb{sub 2}S{sub 3}-CuS thin films indicate the formation of a ternary compound with the structure of famatinite, Cu{sub 3}SbS{sub 4}.

We investigated the correlation among surface chemistry, morphology, and current densities of the charge-discharge processes and the performance of lithium electrodes in Li vs. Li half-cell testing and practical rechargeable AA Li-Li x MnO 2 batteries (Tadiran Batteries, Limited). The electrolyte system was LiAsF 6 /tributylamine (stabilizer)/1,3 dioxolane solution. It was found that the performance of the lithium anodes in practical batteries depends on the current densities at which the batteries are operated. These determine the surface chemistry of the anodes in the following manner: at sufficiently high discharge rates (Li dissolution) the native films which cover the active metal are replaced completely and rapidly by surface films which originate from solvent-reduction processes. These films induce uniform, dendrite-free Li deposition. At too-low discharge rates, part of the native films remains, and thus the surface films are too heterogeneous. This leads to dendritic Li deposition. Charging the batteries at too-high rate (Li deposition) leads to the exposure of fresh Li to the solution, which reacts predominantly with the salt anion (AsF 6 - ). The surface films thus formed (comprised of LiF, Li x AsF y species, etc.) lead to nonuniform Li deposition. It is possible to adjust charging rates which lead to lithium deposition with a very minor exposure of fresh lithium, and thereby change the Li surface chemistry to that dominated by solvent reduction. This leads to an extended cycle life of the Li anodes due to the uniform Li deposition that the surface films thus formed induce.

Parasitic reactions taking place at the carbon anode are primarily responsible for the capacity loss that occurs during the formation cycles of a carbon/LiMn 2 O 4 Li-ion battery. The additional amount of cathode material required to supplement this irreversible capacity leads to a reduction in the specific energy of the battery. This can be overcome with the use of the overlithiated cathode material, Li 1+x Mn 2 O 4 , in which the excess Li, x, is used to compensate the irreversible capacity at the anode. This investigation highlights the usefulness of n-BuLi reduction to synthesize Li 1+x Mn 2 O 4 from LiMn 2 O 4 and demonstrates the long-term rechargeability of these materials in Li cells. Reaction of cubic spinel LiMn 2 O 4 with BuLi to form overlithiated cathode materials of the general formula Li 1+x Mn 2 O 4 (x = 0.1-1.0) was found to be quantitative under mild conditions at room temperature. The X-ray diffraction of each Li 1+x Mn 2 O 4 appeared to represent a nominal composition of a two-phase material consisting of LiMn 2 O 4 and Li 2 Mn 2 O 4 at a-x:x mole ratio, where x represents the number of moles of LiMn 2 O 4 reacted with BuLi. Electrochemical characterization of Li 1+x Mn 2 O 4 indicated that the chemically introduced Li(x in Li 1+x Mn 2 O 4 ) could be extracted nearly 100% in a voltage plateau around 3.0 V vs. Li + /Li. Furthermore, the rate capability and cycle life of these materials when cycled between 4.25 and 3.0 V were identical to those of the baseline LiMn 2 O 4 . In balanced carbon/LiMn 2 O 4 full cells, the chemically inserted Li could be fully utilized to compensate for the irreversible capacity loss occurring in their formation cycles.

Controlled anodic oxidation for achieving a better control of etch depth in AlGaAs semiconductor structures is studied. The rates of material consumption and oxide thickness growth for p ++ -GaAs and p-Al 0.38 Ga 0.89 As are given for the citric acid/glycol/water electrolyte. The etch profiles for GaAs/Al 0.45 Ga 0.55 As and GaAs/Al 0.50 Ga 0.40 As layer sequences in laser diode structures are presented. The underetch is rather high and depends on oxidation conditions (constant voltage or constant current). The profile obtained is very rough for constant voltage oxidation and much better when using constant current conditions. The latter also improves the uniformity of oxide growth. The etch rate of the anodic oxide in diluted HCl is much larger for GaAs than for AlGaAs.

LiMn{sub 2}O{sub 4}-based spinels have been extensively studied as positive electrode materials for lithium-ion batteries. These investigations have shown that, by using the Pechini process, the performance of these materials can be improved significantly through adjustments to the synthesis conditions and composition by means of selective doping. This paper reports the results of neutron and ex situ X-ray diffraction studies performed to examine the structural changes that occur during lithium ion insertion into various Li{sub x}Mn{sub 2}O{sub 4} compositions. It appears that an ordering intercalation of lithium ions occurs in the lithium concentration range of 0.15--0.35, followed by a second-order phase transformation when the lithium population is close to 0.5, leading to a random lithium insertion into a single-spinel phase from x = 0.5 to 1.0.

The authors describe synchrotron based X-ray diffraction techniques and issues related to in situ studies of intercalation processes in battery electrodes. They then demonstrate the utility of this technique, through a study of two batches of Li{sub x}Mn{sub 2}O{sub 4} cathode materials. The structural evolution of these spinel materials was monitored in situ during the initial charge of these electrodes in actual battery cells. Significant differences were observed in the two batches, particularly in the intercalation range of x = 0.45 to 0.20. The first-order structural transitions in this region indicated coexistence of two cubic phases in the batch 2 material, whereas the batch 1 material showed suppressed two-phase coexistence. Batch 2 cells also indicated structural evolution in the low-potential region below 3.0 V in contrast to the batch 1 material. Differences in structural evolution between batches of Li{sub x}Mn{sub 2}O{sub 4} could have important ramifications in their cycle life and stability characteristics.

LiCoO{sub 2} is shown to be a very high rate cathode. Power densities as high as 5,500 W/kg have been demonstrated for Li/LiCoO{sub 2} cells. Such high power was obtained with approximately 75-{micro}m-thick electrodes fabricated with 5 {micro}m or smaller diameter LiCoO{sub 2} particles and having about 65% porosity. A 2 M solution LiAsF{sub 6} in a mixed solvent consisting of 25 vol% propylene carbonate and 75 vol% methyl acetate was the electrolyte. The high Li{sup +} concentration of this electrolyte, together with its room temperature conductivity of 2 {times} 10{sup {minus}2} {Omega}{sup {minus}1} cm{sup {minus}1}, allowed the discharge of Li/LiCoO{sub 2} cells at currents as high as 100 mA/cm{sup 2}. The LiCoO{sub 2} utilization at 50 mA/cm{sup 2} and higher current densities showed a strong dependence on separator porosity. Cells with a 25-{micro}m-thick separator having about 55% porosity showed significantly better power output than ones containing a separator of the same thickness having 32% porosity.

The potential distribution through plastic Li-ion cells during electrochemical testing was monitored by means of three- or four-electrode measurements in order to determine the origin of the poor electrochemical performance (namely, premature cell failure, poor storage performance in the discharged state) of LiMn{sub 2}O{sub 4}/C Li-ion cells encountered at 55 C. Several approaches to insert reliably one or two reference electrodes that can be either metallic lithium or an insertion compound such as Li{sub 4}Ti{sub 5}O{sub 12} into plastic Li-ion batteries are reported. Using a reference electrode, information regarding the evolution of (1) the state of charge of each electrode within a Li-ion cell, (2) their polarization, and (3) their rate capability can be obtained. From these three-electrode electrochemical measurements, coupled with chemical analyses, X-ray diffraction, and microscopy studies, one unambiguously concludes that the poor 55 C performance is mainly due to the instability of the LiMn{sub 2}O{sub 4} phase toward Mn dissolution in LiPF{sub 6}-type electrolytes. A mechanism, based on Mn dissolution, is proposed to account for the poor storage performance of LiMn{sub 2}O{sub 4}/C Li-ion cells.

The composition of the SiON film were optimized to be used as an anneal encapsulation based on the GaAs metal-semiconductor field effect transistor (MESFET) characteristics. The SiON films investigated in the present study were deposited by plasma-enhanced chemical vapor deposition. The refractive indexes of the SiON films with various compositions were found to be useful indicators of film composition. By varying the ratio of the source gases, SiH 4 and N 2 O, we could control the composition to range from SiO 2 to Si 3 N 4 corresponding to refractive indexes from 1.47 to 2.02. MESFET characteristics were evaluated in terms of the Schottky diode ideality factor n, which was found to be highly dependent on the film composition: when we used a SiON film with a refractive index below 1.53, which corresponds to an O-rich composition, the n value exceeded 1.4. This indicates an unstable interface between the GaAs and the SiON. When we used the N-rich SiON, however, such as SiON with a refractive index 1.6, the n value was 1.25. These results are discussed from the viewpoint of interface reaction between GaAs and SiON, which we investigated by using Auger electron spectroscopy.

A solid-state electrochemical cell of the type Pt/LiCoO{sub 2}-5 mole percent (m/o) Co{sub 3}O{sub 4}/Li{sub 2}CO{sub 3} (+5 m/o Li{sub 3}PO{sub 4} + 6 m/o LiAlO{sub 2})/Au, CO{sub 2}, O{sub 2}, was composed for determining CO{sub 2} concentration, where Li{sub 2}CO{sub 3}, a lithium ion conductor, is an electrolyte, and LiCoO{sub 2}-Co{sub 3}O{sub 4} is used as the solid reference electrode. Electromotive force (EMF) of the cell depended logarithmically on the CO{sub 2} partial pressure in CO{sub 2}/O{sub 2} gas mixtures at temperatures between 350 and 400 C. EMF reached a constant value within 1 min after the change of CO{sub 2} partial pressure at 400 C. The sensitivity to CO{sub 2} of this cell was not affected by coexistence of water vapor. The sensor worked stably during a test period of 30 days. The sensing mechanism of CO{sub 2} was discussed together with an explanation to the stability of this sensor.

Recent investigations into the mixed conducting properties of both copper- and gadolinium-doped barium cerates result in an interesting phase, identified as BaCuGd{sub 2}O{sub 5}, which exhibits substantially higher conductivity than any of the doped-barium cerate compounds studied. The predominant portion of the conduction, however, is electronic. Further, composites consisting of BaCuGd{sub 2}O{sub 5} and BaCe{sub 0.8}Gd{sub 0.2}O{sub 3} phases are studied as electrodes for barium cerate-based electrolytes. The composites are shown to have an ionic transference number of about 0.2. As electrodes, the composite material has shown excellent ambipolar transport properties and catalytic activities with interfacial resistances reduced by more than one order of magnitude compared to silver electrodes.

Surface characterization of Ir-based Ti- and Sn-containing electrodes of nominal composition, Ir 0.3 Ti (0.7-x) Sn x O 2 (0 ≤ x ≤ 0.7), was performed ex situ by scanning electron microscopy and energy-dispersive x-ray and in situ by open-circuit potential measurements and cyclic voltammetry. Despite the use of SnCl 2 as precursor, energy-dispersive x-ray results showed the real composition to be very distinct from nominal due to SnCl 4 volatilization during the calcination step in the electrode preparation procedure. SnCl 4 formation in the precursor mixture was confirmed by visible spectrophotometric measurements. The substitution of TiO 2 by SnO 2 results in a significant increase in electrochemically active surface area, as supported by scanning electron microscopy, anodic voltammetric charge, q s , and the double-layer capacity, C dl, as a function of composition. Roughness factors between 3600 and 5100 were obtained. A linear C dl vs. q s graph with an angular coefficient close to one was obtained.

LiCoO{sub 2} the active cathode material in commercial rechargeable lithium batteries, is shown to be a p-type semiconductor, associated with the presence of a small concentration of CO{sup 4+} ions. Its conductivity at room temperature can be increased by over two orders of magnitude, to {approximately}0.5 S/cm, by partial substitution of CO{sup 3+} by Mg{sup 2+} and compensating hole creation. The electrochemical performance of LiMg{sub 0.05} Co{sub 0.95}O{sub 2} is comparable to that of LiCoO{sub 2}; a small reduction in capacity, associated with a reduction in Co{sup 3+} content, occurs but good reversibility is retained and, in contrast to LiCoO{sub 2}, the Mg-doped material is single phase throughout the charge/discharge cycle.

A phenomenological expression of solid-state redox potentials is proposed in order to understand anomalous voltage behaviors of the insertion materials LiCoO 2 , LiCo 1/2 Ni 1/2 O 2 , and LiNiO 2 . The method consists of the superposition of each redox system characterized by Eq. 4 and 5 (see text), describing both one-phase and two-phase reactions by adjusting the interaction-energy parameter zΦ i . For the reaction of □ MeO 2 + yLi → Li y MeO 2 , the reversible electrode potentials, E(y), which are observable, are obtained in a self-consistent manner from the electrochemical density of states. A thus-described solid-state electrochemical reaction consists of three redox systems characterized by E 0i = 4.50, 4.18, and 3.91 V for LiCoO 2 ; 4.23, 3.93, and 3.63 V for LiNiO 2 ; and 4.58, 4.05, and 3.58 V for LiCo 1/2 Ni 1/2 O 2 . From these results the characteristic features of solid-state redox electrodes are described and the significance of this method in materials research for advanced batteries is discussed.

LiNi 1-x Co x O 2 is being considered for use as a cathode material in commercial lithium-ion batteries because of its higher capacity and lower material cost than its end member LiCoO 2 . On the other hand, LiNi 1-x Co x O 2 has better thermal stability than its other end member LiNiO 2 . In this paper we examine the influence of particle size and particle morphology on the electrochemical behavior of LiNi 1-x Co x O 2 and the dependence of the irreversible capacity on Co content, temperature, and particle size. Coin cell performance at room temperature and at 40°C indicates that LiNi 1-x Co x O 2 with a large crystal particle size (P c ) has a low capacity fade rate. The irreversible capacity is reduced at high temperature. By optimizing particle size and cobalt content in LiNi 1-x Co x O 2 , it is possible to achieve cycle performance comparable with LiCoO 2 at room temperature and at 40°C, and have a reversible capacity (between 150 and 200 mAh/g ) substantially higher than LiCoO 2 (140 mAh/g). LiNi 1-x Co x O 2 (0.1 < x < 0.3) tested at C/1 discharge and at 40°C also shows a low capacity fade rate comparable to that of LiCoO 2 material

Polycrystalline samples of Ti{sub 3}SiC{sub 2} were oxidized in air in the 900 to 1,400 C temperature range. The oxidation was parabolic with parabolic rate constants, k{sub p}, that increased from 1 {times} 10{sup {minus}9} to 1 {times} 10{sup {minus}4} kg{sup 2}/m{sup 4}s as the temperature increased from 900 to 1,400 C, respectively, which yielded an activation energy of 370 {+-} 20 kJ/mol. The scale that forms was dense, adhesive, resistant to thermal cyclings and layered. The outer layer was pure TiO{sub 2} (rutile), and the inner layer consisted of mixture of SiO{sub 2} and TiO{sub 2}. The results are consistent with a model in which growth of the oxide layer occurs by the inward diffusion of oxygen and the simultaneous outward diffusion of titanium and carbon. The presence of small volume fractions ({approx} 2%) of TiC{sub x} in Ti{sub 3}SiC{sub 2} were found to have a deleterious effect on the oxidation kinetics.

High sensitivity for specific gas detection has been realized by new gas sensors incorporating multicomponent oxide thin films such as ZnO-In 2 O 3 , MgO-In 2 O 3 , and Zn 2 In0 5 -MgIn 2 O 4 systems. The sensing properties of the multicomponent oxide thin-film sensors were strongly dependent on the composition of the films used. Sensors using ternary compounds such as Zn 2 In 2 O 5 and MgIn 2 O 4 always exhibited a higher sensitivity than those using binary compounds such as ZnO and In 2 O 3 . The sensors only exhibited an increase in resistance with exposure to carbon tetrachloride (CCl 4 ) gas, whereas they exhibited a decrease in resistance for inflammable gases such as butane (C 4 H 10 ) and hexane (C 6 H 14 ). The highest sensitivity for CCl 4 gas was obtained in a sensor using a Zn 2 In 2 O 5 -MgIn 2 O 4 thin film prepared with a Zn 2 In 2 O 5 content of about 60 mole percent. The resistance of sensors operated at 300°C was increased by a factor of about 10 when exposed to CCl 4 gas with a concentration of 350 ppm. The increase in resistance is attributed to the trapping of free electrons resulting from chlorine being adsorbed on grain boundaries and/or the film surface.

The formation efficiency of lead/acid battery positive plates, with and without conductive additives, including barium metaplumbate and a titanium suboxide known as Ebonex®, was compared. The conductive additives significantly enhanced formation, even at a loading level as low as 1%. The enhancement was more pronounced at the early stage of formation when the overall plate conductivity was low. Beyond about 80% theoretical input capacity, the advantage of additives gradually diminished because a conductive network of active material in the plate was established. Formation efficiency, reserve capacity, and cycle life of the plates with and without additives were evaluated. The effects of loading level and particle size of the additives on formation efficiency and plate performance were examined.

A comparison of etch rates for Al{sub x}Ga{sub 1{minus}x}N alloys was performed in Cl{sub 2}Ar and BCl{sub 3}/Ar electron cyclotron resonance plasmas. The etch rates were generally found to decrease with increasing AlN concentration, due to the increasing average bond strengths at higher Al compositions. The fastest rates were found in the Cl{sub 2}/Ar chemistry, with rates of {approximately}3,500 {angstrom}/min for GaN, 1,700 {angstrom}/min for AlN, 2,500 {angstrom}/min for Al{sub 0.31}Ga{sub 0.69}N, and 3,300 {angstrom}/min for Al{sub 0.2}Ga{sub 0.8}N. The etched surfaces were also smoother with the Cl{sub 2}/Ar plasma chemistry than the BCl{sub 3}/Ar plasma chemistry. The etch selectivities for GaN over Al{sub 0.2}Ga{sub 0.8}N, Al{sub 0.3}1Ga{sub 0.69}N, and AlN were quite low, {le}5 for all conditions, and this is due to the ion-driven nature of the removal mechanism.

The (photo)electrochemical and etching properties of n- and p-type In 0.53 Ga 0.47 As in an electrolyte solution (1.3 mol liter -1 H 2 SO 4 ) with and without H 2 O 2 were studied by rotating-disk voltammetry, electrical impedance, and etch rate measurements. It is shown that H 2 O 2 is reduced by a two-hole injection process. In 0.53 Ga 0.47 As is etched efficiently by H 2 O 2 in a combined chemical/electroless etching mechanism, the dissolution intermediates of which appear to be mobile. The observed selectivity of H 2 O 2 for In 0.53 Ga 0.47 As as compared to InP is explained on the basis of the present results. A comparison is made between the electrochemical and etching behavior of In 0.53 Ga 0.47 As and that of common III-V semiconductors such as InP and GaAs.

The layered LiMO{sub 2} (M = Co, Ni) compounds, which are of potential interest for Li-ion batteries, were synthesized at low temperatures by treatment under hydrothermal conditions of LiOH{center_dot}H{sub 2}O aqueous solutions containing powdered H{sub x}MO{sub 2} phases. The authors studied the reaction mechanism and the influence of temperature, pressure, water dilution, and precursor ratio on the degree of progress of the ion exchange process. Single-phase LiMO{sub 2} can be obtained in 48 h at 160 C under an air pressure of 60 bars from an MOOH/LiOH{center_dot}H{sub 2}O/H{sub 2}O mixture. The degree of advancement of the exchange reaction for M = Co was monitored in situ using an autoclave which allows the withdrawal of samples in the course of the reaction. From transmission electron microscopy coupled with x-ray diffraction studies the authors conclude that the reaction occurs by surface H{sup +}/Li{sup +} exchange and is accompanied by a progressive breaking of the particles due to an interfacial collapse phenomenon. Infrared studies indicate that the LiCoO{sub 2} and LiNiO{sub 2} phases obtained are contaminated by carbonates that can more easily be eliminated in the case of LiCoO{sub 2} by water washing and post-heating treatments under primary vacuum at 200 C formore » 2 days. Once the ion-exchange parameters are controlled, the LiMO{sub 2} products exhibit electrochemical performances comparable to those of high-temperature made phases.« less

Electrochemical, thermal, and structural characterization of lithium insertion processes into orthorhombic Na{sub x}MnO{sub 2}-based materials is presented. Chimie douce oxidation, reduction, and/or exchange reactions of the precursor Na{sub 0.44}MnO{sub 2} can be used to prepare high capacity (180 mAh/g), high potential compounds for use in secondary lithium batteries. Lithiated Na{sub x}MnO{sub 2} is quite stable; formation of spinel phases occurs only under conditions of prolonged severe abuse during cycling in electrochemical cells, or upon heating to 500 C. The lithium-ion intercalation process is considerably more complex than that for sodium ions; features are seen in the electrochemical potential-step experiments that may be attributed to several phase transitions. These results are interpreted in terms of the unusual structure, and implications for future use of these materials in lithium batteries are discussed.

Samples of CuInSe{sub 2} with a wide composition range were prepared by electrodeposition from Cu(II), In(III), and Se(IV) precursors. According to the preparation conditions, sample groups were defined and characterized for their structural, optical, and photovoltaic properties. A postthermal treatment was carried out in order to improve the quality of the as-deposited films. Strong correlations with the film composition are clearly evident with respect to the deposition conditions. Sample groups exhibit different properties, which are analyzed in terms of deviations from molecularity ({Delta}m) and stoichiometry ({Delta}s).

Supercritical drying of V 2 O 5 gels yields amorphous aerogels (ARG) that serve as reversible, high capacity hosts for lithium ion intercalation. We have found that ARG material consists of a highly interconnected solid network that has a surface area up to 450 m 2 /g and a specific pore volume of 2.3 cm 3 /g. The material hosts at least 4 Li + per mole of V 2 O 5 (ARG) as determined by both galvanostatic intermittent titration (GITT) and chemical lithiation (CL) techniques. The equilibrium voltage-composition curve is identical for both GITT and CL techniques as well. V 2 O 5 (ARG) has a specific energy in excess of 1600 Wh/kg, the highest ever reported for any vanadium oxide host

In this paper the authors report on the characteristics and performance of a new rechargeable Li-Li{sub x}MnO{sub 2} 3 V battery system developed at Tadiran. The behavior of AA cells of an 800 to 750 mAh capacity is described in terms of charge-discharge curves, cycle life, and low-temperature and high-current performance. At charging regimes around C/10, more than 350 cycles at 100% DOD could be obtained. These batteries have a unique cell chemistry based on LiAsF{sub 6}/1,3-dioxolane/tributyl amine electrolyte solutions which provide internal safety mechanisms that protect the cells from short circuit, overcharge, and thermal runaway upon heating up to 135 C. This behavior is due to the fact that the electrolyte solution is stable at low-to-medium temperatures but polymerizes at temperatures over 125 C.

Deterioration of an InBO 3 :Tb phosphor screen deposited in potassium silicate solution was studied by a demountable apparatus designed to simulate the tube condition. Evolution of oxygen from the phosphor crystal was observed under intense electron irradiation. It was found that the deterioration is accelerated by phosphor screen heating, which depends on the screen weight, packing density, and an amount of silica gel deposited between particles and the surface of the screen.

The preparation and characterization of spinel LiMn{sub 2}O{sub 4} having small average particle sizes (

Rare earth oxide doped BaCeO 3 is known to exhibit high protonic conductivity in the temperature range 500 to 900°C and is a potential electrolyte for use in hydrogen sensing and fuel cell applications. Prior work, however, has shown that BaCeO 3 may be thermodynamically unstable at low temperatures. In the present work, the stability of BaCe0 3 in an H 2 O vapor containing environment was investigated by exposing powder and sintered samples to ∼430 Torr H 2 O in the temperature range 500 to 900°C. All BaCeO 3 samples decomposed into CeO 2 and Ba(OH) 2 in relatively short periods of time at temperatures less than 900°C. Doped BaCeO 3 decomposed at a faster rate than the undoped BaCeO 3 . Sintered BaCeO 3 decomposed at a rate comparable to the powder samples. These results establish that BaCeO 3 is thermodynamically unstable when a critical H 2 O vapor pressure is exceeded and that the rapid decomposition of both powder and sintered samples is the result of the high solubility of H 2 O in BaCeO 3 which accelerates the kinetics of decomposition.

Lithium nickel oxide, used as the positive electrode in lithium batteries, crystallizes in the rhombohedral system (SG:R{bar 3}m) with a layered structure. In fact, stoichiometric LiNiO{sub 2} has never been reported. The true formula is Li{sub 1{minus}z}Ni{sub 1+z}O{sub 2} (0.00 < z < 0.20); z is dependent on the experimental conditions. This nonstoichiometry leads to a strong decrease of the battery performance. Therefore, several methods of preparation were investigated to synthesize stoichiometric LiNiO{sub 2}. The Li{sub 0.98}Ni{sub 1.02}O{sub 2} composition, which is very close to the ideal one, was obtained from a mixture of Li{sub 2}O and NiO heated at 700 C. This quasi-2D LiNiO{sub 2} was submitted to several thermal treatments, in order to determine the influence of the temperature on the composition. Purposely lithium deficient phases were also prepared. Correlations between the composition of each material (deduced from the Rietveld refinement of the X-ray diffraction pattern) and the magnetic and electrochemical behavior are discussed.

Quaternary Li-Mn-V-O spinels formed from heating mixtures of LiNO{sub 3}, MnCO{sub 3}, and NH{sub 4}VO{sub 3} around 350{degree} have been characterized by electrochemical measurement, X-ray photoelectron spectroscopy, X-ray diffractometry, {sup 7}Li-NMR, and magnetic susceptibility measurements. These results were compared with those for ternary Li-Mn-O spinels prepared at 350 and 850 C. The compositions of the quaternary and ternary spinels formed at 350 C were shown to be x(Li{sub 2}O)Mn{sub 2}O{sub 4} {center_dot} yV{sub 2}O{sub 5} (x = 0.5 {approximately} 1, y = 0 {approximately} 0.4). The cubic a{sub 0}-lattice parameter and specific density of the quaternary spinels increased with increasing vanadium content in the spinel structure. The {sup 7}Li-NMR measurements revealed that the quaternary spinels did not show any Knight shift, while the ternary Li-Mn-O spinels formed at 350 and 850 C had a large Knight shift of 490 {approximately} 535 ppm in reference to LiCl. Furthermore, the measurement of the magnetic susceptibility indicated that the ternary and quaternary spinels formed at 350 C are paramagnetic and the ternary LiMn{sub 2}O{sub 4} prepared at 850 C is antiferromagnetic.

The change in sheet resistance of an SF 6 /CHF 3 plasma-exposed Al x Ga 1-x As (x = 0.30, 0.15) epilayer before and after annealing was investigated and compared with that for GaAs. The sheet resistance of plasma-exposed Al x Ga 1-x As (x = 0.30, 0.15) increases further after 300°C annealing, while that of GaAs remained unchanged. After 450°C annealing, the resistivity of plasma-exposed Al x Ga 1-x As (x = 0.30) was still higher, while damage in Al x Ga 1-x As (x = 0.15) and GaAs had completely vanished. The increased resistivity in Al x Ga 1-x As (x = 0.30, 0.15) after annealing was mainly due to further carrier reduction after annealing was mainly due to further carrier reduction by magnification of the damaged region. The effect of annealing on He plasma-exposed AlGaAs was similar to that for SF 6 /CHF 3 -plasma-exposed AlGaAs, which suggests that the increased sheet resistance after annealing is related to incorporated low-mass ions, such as He and H. The 4.2 K photoluminescence measurements revealed a new spectral peak near 1.70 eV after annealing, and the peak intensity for the SF 6 /CHF 3 and He plasma-exposed samples was prominent. These results suggest that in-diffusion of point defects by light ions during the annealing extends the carrier reduction in AlGaAs to greater depth.

An in situ technique utilizing a linear voltage displacement transducer device for investigating the thickness changes occurring during the cycling of a lithium insertion type rechargeable cell based on a composite V{sub 6}O{sub 13} cathode is described. The authors believe the method is generally applicable to other battery systems which undergo expansion/contraction effects during normal operation. During cell discharge there is a gradual decrease in cell thickness, while the converse is true during the subsequent charging process. The thickness changes are highly reversible over the single cycle considered. The variation of cell thickness was approximately linear with depth of discharge. For the cell in the fully discharged state, the overall thickness change of the active cell components was {approximately}6%. When the thickness variation associated with the lithium electrode is excluded from the calculations, the V{sub 6}O{sub 13} cathode increases in thickness during cell discharge and decreases during cell change. The changes are consistent with the literature-reported V{sub 6}O{sub 13} cathode unit cell expansion/contraction effects caused by the lithium insertion/extraction processes.

Photoelectrolysis of water at ambient temperature (25 C) into hydrogen and oxygen thermodynamically requires a free energy of 1.23 eV. GaInP{sub 2} was identified as a promising material since its bandgap (1.8 to 1.9 eV) is ideal for this reaction. However, previous work determining the flatband potential of p-GaInP{sub 2} has revealed that the position of the bandedges are from 100 to 400 meV too negative for water splitting. The surface of epi layer p-GaInP{sub 2} electrodes was treated using 8-quinolinol, cupferron, and ferrocyanide, producing a modified surface directed at varying the Helmholtz layer charge. Mott-Schottky and photocurrent-voltage measurements were carried out to determine if there was any shift in the flatband potential or change in the onset of photocurrent due to the altered surface charge. Treatments with 8-quinolinol and cupferron were found to shift the flatband to more positive potentials; treatments with ferrocyanide produced a negative shift. The quinolate-modified interface had flatband potentials that were pH independent in the range 5 through 8. Photoluminescence studies on electrodes that were etched, treated with 8-quinolinol, and exposed to air for long periods showed no degradation of the luminescence intensity or photoluminescence decay time, in contrast to untreated electrodes.

CuInSe{sub 2} thin films have been obtained from different precursors prepared by direct or sequential electrodeposition processes. The nature of the as-deposited layers and the evolution of the films during the heat-treatment in an inert (vacuum) or a reactive (elemental Se vapor) atmosphere have been studied by X-ray diffraction and X-ray photoelectron spectroscopy analysis. The chemistry of the different phase transformations occurring as a function of the annealing temperature has been examined, and possible reaction pathways for the formation of CuInSe{sub 2} are presented. The results show that high crystalline chalcopyrite CuInSe{sub 2} films with the desired composition can be obtained after annealing either direct or sequentially electrodeposited precursors at 400 C. An improvement in film quality can be gained by using an electrodeposited Cu layer as growth surface for the CuInSe{sub 2} formation. If elemental Se is also added during the heat-treatment, then a higher recrystallization of the films is observed.