Structure and Electrochemical Properties of LiMn2O4 Thin Films

The structure and electrochemical properties of LiMn{sub 2}O{sub 4} films depend upon the deposition and annealing conditions. Films which were deposited by rf magnetron sputtering of LiMn{sub 2}O{sub 4} in Ar + N{sub 2} gas mixtures and annealed in O{sub 2} at temperatures between 400 to 1000{degrees}C had the cubic spinel structure with an a-axis length that increased linearly from 8.13 to 8.25 {Angstrom} with increasing anneal temperature. Thin-film lithium cells with cathodes of different a-axis lengths exhibited marked differences in their voltage profiles. In particular, the ratio of the capacities at 4 V and 3 V increased with the a-axis length. A defect model of LiMn{sub 2}O{sub 4} which is consistent with the structural and electrochemical data is represented by [Li{sub 1-y+z}Mn{sup 2+}{sub y-z}]{sub 8a}[Mn{sup 2+}{sub z}]{sub 16c}[Li{sub x}Mn{sub 2-x}]{sub 16d}O{sub 4}. Based on this model and the results of in-situ XRD measurements, it is proposed that Mn ions migrate from 8(a) tetrahedral sites to 16(c) octahedral sites on charging the cells in the 5V plateau

Optical properties of multicomponent antimony-silver nanoclusters formed in silica by sequential ion implantation

The linear and nonlinear optical properties of nanometer dimension metal colloids embedded in a dielectric depend explicitly on the electronic structure of the metal nanoclusters. The ability to control the electronic structure of the nanoclusters may make it possible to tailor the optical properties for enhanced performance. By sequential implantation of different metal ion species multi-component nanoclusters can be formed with significantly different optical properties than single element metal nanoclusters. The authors report the formation of multi-component Sb/Ag nanoclusters in silica by sequential implantation of Sb and Ag. Samples were implanted with relative ratios of Sb to Ag of 1:1 and 3:1. A second set of samples was made by single element implantations of Ag and Sb at the same energies and doses used to make the sequentially implanted samples. All samples were characterized using RBS and both linear and nonlinear optical measurements. The presence of both ions significantly modifies the optical properties of the composites compared to the single element nanocluster glass composites. In the sequentially implanted samples the optical density is lower, and the strong surface plasmon resonance absorption observed in the Ag implanted samples is not present. At the same time the nonlinear response of the these samples is larger than for the samples implanted with Sb alone, suggesting that the addition of Ag can increase the nonlinear response of the Sb particles formed. The results are consistent with the formation of multi-component Sb/Ag colloids

Weight change measurements of erosion/deposition at beryllium limiter tiles in ISX-B

The weight changes of Be tiles which functioned as a rail limiter in ISX-B for more than 3500 beam-heated discharges have been determined. The net weight loss for the limiter was 2.0 g, with the central tiles losing a total of 3.2 g and inboard tiles gaining 1.2 g. The weight loss is attributed primarily to the release of Be droplets as a result of limiter surface melting. The weight gains resulted from an inward flow of molten material along the limiter surface. The results indicate high erosion (melt loss) with incomplete and nonuniform redeposition (melt flow) of limiter material during periods of limiter melting

Sputter deposition and characterization of lithium cobalt oxide thin films and their applications in thin-film rechargeable lithium batteries

Li Co oxide thin films were deposited by rf magnetron sputtering of a LiCoO{sub 2} target in a 3:1 Ar/O{sub 2} mixture gas. From proton-induced gamma-ray emission analysis and Rutherford backscattering spectrometry, the average composition of these films was determined to be Li{sub 1.15}CoO{sub 2.16}. X-ray powder diffraction patterns of films annealed in air at 500-700 C were consistent with regular rhombohedral structure of crystalline LiCoO{sub 2}. Discharge curves of thin film lithium cells with amoprohous LiCoO{sub 2} showed no obvious structural transition between 4.2 and 1.5 V. Shape of discharge curves of cells with polycrystalline cathodes were consistent with a two-phase voltage plateau at {similar_to}3.9 V with a relatively large capacity and two additional smaller plateaus at higher voltages. Cells with the 700 C annealed cathodes showed a capacity loss of {similar_to} after 1000 cycles between 4.2 and 3.0 V

Ionic Conductivities of Lithium Phosphorus Oxynitride Glasses, Polycrystals and Thin Films

Various lithium phosphorus oxynitrides have been prepared in the form of glasses, polycrystals, and thin films. The structures of these compounds were investigated by X-ray and neutron diffraction, X-ray photoelectron spectroscopy (XPS), and high-performance liquid chromatography (HPLC). The ac impedance measurements indicate a significant improvement of ionic conductivity as the result of incorporation of nitrogen into the structure. In the case of polycrystalline Li{sub 2.88}PO{sub 3.73}N{sub 0.14} with the {gamma}-Li{sub 3}PO{sub 4} structure, the conductivity increased by several orders of magnitude on small addition of nitrogen. The highest conductivities in the bulk glasses and thin films were found to be 3.0 {times} 10{sup -7} and 8.9 {times} 10{sup -7} S{center_dot}cm{sup -1} at 25{degrees}C, respectively

Surface probe measurements in ISX-B and EBT-S

Surface deposition probe techniques have been shown to be an effective means of determining the characteristics of the plasma edge region of magnetic confinement devices. Experimental results on ISX-B and EBT-S have led to a consistent picture of the edge plasma and the dominant impurity introduction mechanisms. This picture is supported by numerous other measurements and emphasizes the importance of concentrating several techniques on the complex problems of plasma fusion

Characterization of the TEXTOR plasma edge using deposition probe techniques

Carbon and single crystal silicon passive deposition probes were used to measure the characteristics of the plasma edge region of the TEXTOR tokamak. Analysis of the probes was done by Rutherford backscattering for impurities and nuclear reaction analysis and elastic recoil detection for hydrogen isotopes. Plasma fluxes and energies in the edge were measured using probe techniques. The principal impurities in the plasma edge were determined and their behavior as a function of time and position was measured. Measurements were also made of in situ erosion rates. The results are compared with independent measurements of other plasma parameters to study possible impurity introduction mechanisms. This work represents the first deposition probe measurements made in the plasma edge of TEXTOR

Accelerator-based plasma-wall interaction studies on the TEXTOR tokamak

Deposition probes are commonly used to determine plasma edge characteristics in tokamaks. Such probes are frequently analyzed using accelerator-based techniques and can yield information on impurity fluxes, hydrogen fluxes and energies, and surface erosion rates in the plasma edge. Several types of deposition probes have been employed to investigate the plasma edge region of the TEXTOR tokamak in Juelich, FRG. TEXTOR is a moderate size tokamak (major radius = 1.75 m) that is capable of 2 to 3 s discharges and contains a liner that can be heated to 600/sup 0/C. These capabilities make TEXTOR particularly attractive for the study of plasma-wall interactions. Several countries, including the United States, Sweden and the host nation, are carrying on active research programs in the area of plasma-edge studies. This research has included measurements of plasma, impurity, and power fluxes at various radii in the scrapeoff layer. The results achieved in characterizing the plasma edge in these recent probe studies on TEXTOR will be reviewed

Optical and magnetic properties of silica implanted with N{sup +} and Fe{sup +}

Silica platelets (Corning 7940) were implanted sequentially with N{sup +} at 52 keV to different doses ranging from 0 to 1.2{times}10{sup 17} ions cm{sup {minus}2} and then with Fe{sup +} at 160 keV to a dose of 6{times}l0{sup 16} ions cm{sup {minus}2}. The optical absorption decreased with increasing N{sup +} dose at photon energies ranging from 1.4 to 6.5 eV. The relative intensity, S(0{degrees}), of the ferromagnetic resonance absorption and its resonance field, H{sub s}(0{degrees}), at {theta}=0{degrees} were larger than S(90{degrees}) and H{sub s}(90{degrees}), at {theta}=0{degrees}, where {theta} is the angle between the applied magnetic field and the normal to the implanted surface. The maximum values of S(0{degrees}) and S(90{degrees}) were observed near the N/Fe atomic ratio of 0.2. At the similar atomic ratio, the differential relative intensity, S(0{degrees}){minus} S(90{degrees}), and the differential resonance field, H{sub s}(0{degrees}){minus} H{sub s}(90{degrees}), associated with the degree of magnetic interaction between the produced compounds, also showed maxima. We conclude that sequential ion-implantation of N{sup +} and Fe{sup +} into silica causes a chemical interaction to produce iron nitrides