83 Matching Results

Search Results

Advanced search parameters have been applied.

Reconstruction of surfaces in NiO

Description: We studied the reconstructions of surfaces in NiO by atomistic simulations which utilize Buckingham short range potentials and the shell model. It was found that (hk0) surfaces prefer to reconstruct into (100) surface facets which has the lowest energy. The interaction between these (100) facets is repulsive and converges to zero as size of facets grows. The (111) surface can be stabilized by reconstruction into (100) micro-facets.
Date: July 1, 1995
Creator: Yan, M. & Chen, S.P.
Partner: UNT Libraries Government Documents Department

Stoichiometry, structure, and properties of La{sub 2}NiO{sub 4+{delta}} and La{sub 2-x}Sr{sub x}NiO{sub 4{+-}{delta}}

Description: The oxygen content phase diagram of La{sub 2}NiO{sub 4+{delta}} has been studied in detail using x-ray and neutron diffraction data from well-characterized specimens. There are numerous phase separations and phase transitions which are observed with changes in temperature and composition. The complexity of the phase diagram arises primarily from oxygen defect interactions, however the authors have also obtained evidence for coupled charge and spin ordering at {delta} = 0.125 corresponding to organization of holes into ordered domain walls. These domain walls act as antiphase boundaries between stripes of antiferromagnetically ordered nickel moments. Neutron scattering data on Sr-substituted compositions with well-defined oxygen content indicate incommensurate charge and spin correlations closely related to those in the x=0, {delta} = 0.125 composition. The incommensurability approaches 1/4 and the correlation length increases as the hole concentration approaches p = x+2{delta} = 0.25.
Date: March 1, 1995
Creator: Buttrey, D.J.; Sachan, V.; Tranquada, J.M. & Lorenzo, J.E.
Partner: UNT Libraries Government Documents Department

Dynamics of metal/ceramic interface formation.

Description: We summarize the work of the Laboratory Directed Research and Development (LDRD) project 'Dynamics of Metal/Ceramic Interface Formation.' Low-energy electron microscopy (LEEM) was used to monitor in real time how the metal/ceramic interface between the alloy NiAl and its oxide formed. The interfaces were synthesized by exposing the clean alloy to oxygen at either low or high temperature. During low-temperature exposure, an initially amorphous oxide formed. With annealing, this oxide crystallizes into one type of alumina that has two orientational domains. While the oxide is relatively uniform, it contained pinholes, which coarsened with annealing. In marked contrast, high-temperature exposure directly produced rod-shaped islands of crystalline oxide. These rods were all aligned along the substrate's [001] direction and could be many microns in length. Real-time observations showed that the rods can both grow and shrink by addition and subtraction, respectively, at their ends.
Date: December 1, 2003
Creator: McCarty, Kevin F.
Partner: UNT Libraries Government Documents Department

Stoichiometry, spin fluctuations, and superconductivity in LaNiPO

Description: Superconductivity in LaNiPO is disrupted by small ({approx}5%) amounts of non-stoichiometry on the lanthanum site, even though the electronic contribution to the heat capacity increases with increasing non-stoichiometry. All samples also exhibit specific heat anomalies consistent with the presence of ferromagnetic spin fluctuations (T{sub sf}{approx} 14K). Comparison of layered nickel phosphide and nickel borocarbide superconductors reveals different structure-property correlations in the two families.
Date: January 1, 2009
Creator: Klimczuk, Tomasz; Mcqueen, Tyrel M; Williams, Anthony J; Huang, Qiang & Cava, Robert J
Partner: UNT Libraries Government Documents Department

NiO exchange bias layers grown by direct ion beam sputtering of a nickel oxide target

Description: A new process for fabricating NiO exchange bias layers has been developed. The process involves the direct ion beam sputtering (IBS) of a NiO target. The process is simpler than other deposition techniques for producing NiO buffer layers, and facilitates the deposition of an entire spin-valve layered structure using IBS without breaking vacuum. The layer thickness and temperature dependence of the exchange field for NiO/NiFe films produced using IBS are presented and are similar to those reported for similar films deposited using reactive magnetron sputtering. The magnetic properties of highly textured exchange couples deposited on single crystal substrates are compared to those of simultaneously deposited polycrystalline films, and both show comparable exchange fields. These results are compared to current theories describing the exchange coupling at the NiO/NiFe interface.
Date: March 1, 1996
Creator: Michel, R.P.; Chaiken, A.; Johnson, L.E. & Kim, Y.K.
Partner: UNT Libraries Government Documents Department

Magnetic coupling in spin-valves from magnetic circular dichroism

Description: The authors have applied magnetic x-ray circular dichroism (MXCD) to extract elemental magnetic moments for real, thin-film spin valve devices and demonstrated the correlation between MXCD and R-H measurements on those devices. The spin valves consisted of NiFe/Co/Cu/Co/NiFe sandwiches with variable Cu spacer-layer thickness, grown on a thick NiO film, as described previously. One permalloy layer is therefore magnetically pinned to the substrate which it contacts. Spin-polarized, X-ray absorption spectra were collected using beamline 8-2 at the Stanford Synchrotron Radiation Laboratory. The Poynting vector of the incident beam was aligned at grazing incidence to the films, either parallel or antiparallel to their remanent magnetization. For each spin valve, four absorption spectra were collected, With the remanent magnetization initially parallel to the incident beam direction, a pair of spectra were recorded, one with the helicity of the incident photons parallel to the remanent magnetization of the device, and one with their helicity antiparallel to the remanent magnetization. Next, the samples were rotated in order to align their remanent magnetization antiparallel to the incident beam direction, and a pair of absorption spectra was similarly obtained from beams polarized with opposite helicity. Finally, each absorption spectrum was normalized to the incident photon flux.
Date: December 18, 1995
Creator: Bedrossian, P.J.; Tobin, J.G.; Jankowski, A.F.; Waddill, G.D.; Anthony, T.C. & Brug, J.A.
Partner: UNT Libraries Government Documents Department

Evidence for strong electron-lattice coupling in La{sub 2{minus}x}Sr{sub x}NiO{sub 4}

Description: The inelastic neutron scattering spectra were measured for several Sr concentrations of polycrystalline La{sub 2{minus}x}Sr{sub x}NiO{sub 4}. The authors find that the generalized phonon density-of-states is identical for x = 0 and x = 1/8. For x = 1/3 and x = 1/2, the band of phonons corresponding to the in-plane oxygen vibrations (> 65 meV) splits into two subbands centered at 75 meV and 85 meV. The lower frequency band increases in amplitude for the x = 1/2 sample, indicating that it is directly related to the hole concentration. These changes are associated with the coupling of oxygen vibrations to doped holes which reside in the NiO{sub 2} planes and are a signature of strong electron-lattice coupling. Comparison of La{sub 1.9}Sr{sub 0.1}CuO{sub 4} and La{sub 1.875}Sr{sub 0.125}NiO{sub 4} demonstrates that much stronger electron-lattice coupling occurs for particular modes in the cuprate for modest doping and is likely related to the metallic nature of the cuprate.
Date: April 1, 1999
Creator: McQueeney, R.J. & Sarrao, J.L.
Partner: UNT Libraries Government Documents Department

Electrochromic lithium nickel oxide by pulsed laser deposition and sputtering

Description: Thin films of lithium nickel oxide were deposited by sputtering and pulsed laser deposition (PLD) from targets of pressed LiNiO{sub 2} powder. The composition and structure of these films were analyzed using a variety of techniques, such as nuclear-reaction analysis, Rutherford backscattering spectrometry (RBS), x-ray diffraction, infrared spectroscopy, and atomic force microscopy. Crystalline structure, surface morphology and chemical composition of Li{sub x}Ni{sub 1{minus}x}O thin films depend strongly on deposition oxygen pressure, temperature as well as substrate-target distance. The films produced at temperatures lower than 600 C spontaneously absorb CO{sub 2} and H{sub 2}O at their surface once they are exposed to the air. The films deposited at 600 C proved to be stable in air over a long period. Even at room temperature the PLD films are denser and more stable than sputtered films. RBS determined the composition of the best films to be Li{sub 0.5}Ni{sub 0.5}O deposited by PLD at 60 mTorr O{sub 2} pressure. Electrochemical tests show that the films exhibit excellent reversibility in the range 1.0 V to 3.4 V versus lithium. Electrochemical formatting which is used to develop electrochromism in other films is not needed for the stoichiometric films. The optical transmission range is almost 70% at 550 nm for 150-nm thick films. Devices made from these films were analyzed using novel reference electrodes and by disassembly after cycling.
Date: September 1, 1996
Creator: Rubin, M.; Wen, S.J.; Richardson, T.; Kerr, J.; Rottkay, K. von & Slack, J.
Partner: UNT Libraries Government Documents Department

Rietveld refinement of YBa{sub 2}Cu{sub 3-x}Ni{sub x}O{sub y} prepared by quenching and oxygen gettering

Description: We have refined the structures for YBa{sub 2}Cu{sub 2.94}Ni{sub 0.06}O{sub y} (2% Ni) and YBa{sub 2}Cu{sub 2.80}Ni{sub 0.20}O{sub y} (6.67% Ni) at y {approximately} 6.95 and y {approximately} 6.5 contents. Oxygen was reduced by two independent methods: quenching from 690{degrees}C and oxygen gettering at 450{degrees}C. Cu-0 bond lengths were calculated based on Rietveld structure refinements for the various samples; they indicate the likely occupancy of Ni in the plane (Cu2) site of the 123 superconductor.
Date: October 1, 1995
Creator: Rodriguez, M.; Eatough, M. & Licci, F.
Partner: UNT Libraries Government Documents Department

Transition metal catalysis in the generation of petroleum and natural gas. Final report, September 1, 1992--October 31, 1995

Description: This project originated on the premise that natural gas could be formed catalytically in the earth rather than thermally as commonly believed. The intention was to test this hypothetical view and to explore generally the role of sedimentary metals in the generation of light hydrocarbons (C1 - C9). We showed the metalliferous source rocks are indeed catalytic in the generation of natural gas. Various metal compounds in the pure state show the same levels of catalytic activity as sedimentary rocks and the products are identical. Nickel is particularly active among the early transition metals and is projected to remain catalytically robust at all stages of catagenesis. Nickel oxide promotes the formation of n-alkanes in addition to natural gas (NG), demonstrating the full scope of the hypothetical catalytic process. The composition of catalytic gas duplicates the entire range of natural gas, from so-called wet gas to dry gas (60 to 95+ wt % methane), while gas generated thermally is consistently depleted in methane (10 to 60 wt % methane). These results support the view that metal catalysis is a major pathway through which natural gas is formed in the earth.
Date: January 21, 1997
Creator: Mango, F.D.
Partner: UNT Libraries Government Documents Department

Thermal characterization of Li-ion cells using calorimetric techniques

Description: The thermal stability of Li-ion cells with intercalating carbon anodes and metal oxide cathodes was measured as a function of state of charge and temperature for two advanced cell chemistries. Cells of the 18650 design with Li{sub x}CoO{sub 2} cathodes (commercial Sony cells) and Li{sub x}Ni{sub 0.8}Co{sub 0.2}O{sub 2} cathodes were measured for thermal reactivity. Accelerating rate calorimetry (ARC) was used to measure cell thermal runaway as a function of state of charge (SOC), microcalorimetry was used to measure the time dependence of thermal output, and differential scanning calorimetry (DSC) was used to study the thermal reactivity of the individual components. Thermal decomposition of the anode solid electrolyte interphase (SEI) layer occurred at low temperatures and contributes to the initiation of thermal runaway. Low temperature reactions from 40 C--70 C were observed during the ARC runs that were SOC dependent. These reactions measured in the microcalorimeter decayed over time with power-law dependence and were highly sensitive to SOC and temperature. ARC runs of aged and cycled cells showed complete absence of these low-temperature reactions but showed abrupt exothermic spikes between 105--135 C. These results suggest that during aging the anode SEI layer is decomposing from a metastable state to a stable composition that is breaking down at elevated temperatures.
Date: May 31, 2000
Creator: ROTH,EMANUEL P.
Partner: UNT Libraries Government Documents Department

In-situ x-ray diffraction of layered LiCoO{sub 2}-Type cathode materials

Description: The authors have investigated LiNi{sub 0.8}Co{sub 0.2}O{sub 2} (Sumitomo) and LiNi{sub 5/8}Co{sub 1/4}Mn{sub 1/16}Al{sub 1/16}O{sub 2} (Sandia chemical preparation method) cathode powders via in-situ X-ray Diffraction and Cyclic Voltammetry using a coffee-bag type electrochemical cell. Both cathode materials did not show a monoclinic distortion during de-intercalation but sustained the hexagonal structure up to 4.3 V. The doping of Co into the LiNiO{sub 2} structure appears to stabilize this lattice as the hexagonal structure over the full range of charging (up to 4.3 V). The LiNi{sub 5/8}Co{sub 1/4}Mn{sub 1/16}Al{sub 1/16}O{sub 2} cathode material exhibited a 160 mAh/g capacity (to 4.1 V) on its 1{sup st} cycle, while displaying a much smaller volume change (as compared to LiNi{sub 0.8}Co{sub 0.2}O{sub 2}) during de-intercalation. This reduced overall volume change (2.5 vol%) may have important implications for cycle life of this material.
Date: December 9, 1999
Creator: Rodriguez, M.A.; Ingersoll, D. & Doughty, D.H.
Partner: UNT Libraries Government Documents Department

Surface modification of nickel battery electrodes by cobalt plasma immersion ion implantation and deposition

Description: Nickel hydroxide is the electrochemically active material in the positive electrode of several important rechargeable alkaline-electrolyte batteries. It is believed that divalent Ni(OH){sub 2} is converted to trivalent NiOOH as the electrode is electrochemically oxidized during the battery charging process, and the reverse reaction (electrochemical reduction) occurs during battery discharge, however the details of this process are not completely understood. Because these electrochemical reactions involve surface charge-transfer processes, it is anticipated that surface modification may result in improved battery performance. We used broad-beam metal ion implantation and Metal Plasma Immersion Ion Implantation and Deposition to add cobalt and other species to the nickel electrode surface. The principle of the latter technique is explained in detail. It is shown that implanted and deposited cobalt ions act as a dopant of Ni(OH){sub 2}, and thereby alter its electronic conductivity. This electronic effect promotes lateral growth of NiOOH nodules and more-complete conversion of Ni(OH){sub 2} to NiOOH, which can be interpreted in terms of the nodule growth model. Other dopants such as Au, W, Pb, Ta and Ti{sub 4}O{sub 7} were also tested for suppressing the parasitic oxygen evolution reaction in rechargeable nickel cells.
Date: February 1, 1995
Creator: Anders, S.; Anders, A.; Brown, I.; Kong, F. & McLarnon, F.
Partner: UNT Libraries Government Documents Department

Giant oxygen isotope effect on the metal-insulator transition of RNiO{sub 3} perovskites

Description: The metal to insulator transition displayed by all the members of the perovskite family RNiO{sub 3} (R = 4f rare earth different from La) has attracted a lot of interest since it constitutes one of the few examples of this phenomenon in perfectly stoichiometric compounds. In spite of the great deal of work performed during the last six years, the mechanism responsible for the electronic localization is still a matter of controversy. The observation of unusually large O isotope shifts on the metal-insulator temperature T{sub MI} reported in this study represents an important advance since it clearly proves the dominant role of the electron lattice interaction as driving force for the transition. Moreover, the good agreement between this observation and a simple model based on the existence of Jahn-Teller polarons in the metallic state gives further qualitative and quantitative support to the polaronic picture recently suggested to account for O isotope effects in other 3d transition metal oxides containing Jahn-Teller ions.
Date: August 1, 1998
Creator: Medarde, M.; Fauth, F.; Furrer, A.; Lacorre, P. & Conder, K.
Partner: UNT Libraries Government Documents Department

Spectral properties of the 2D Holstein t-J model

Description: Employing the Lanczos algorithm in combination with a kernel polynomial moment expansion (KPM) and the maximum entropy method (MEM), we show a way of calculating charge and spin excitations in the Holstein t-J model, including the full quantum nature of phonons. To analyze polaron band formation we evaluate the hole spectral function for a wide range of electron-phonon coupling strengths. For the first time, we present results for the optical conductivity of the 2D Holstein t-J model.
Date: December 31, 1996
Creator: Fehske, H.; Wellein, G.; Bauml, B. & Silver, R.N.
Partner: UNT Libraries Government Documents Department

XPS study of Ni-Fe manganite thermistor material

Description: The resistivity of the as-fabricated thermistor material, nickel-iron-manganite, changes during initial aging in the temperature range of 150-300{degrees}C before becoming stable. X-ray photoelectron spectroscopy (XPS) was used to determine if any valency change or chemical shift of the cations or oxygen occurred after aging. The goal of the study was to identify any ionic changes that might affect thermistor stability. The only observed changes in 2p{sub 3/2} peaks due to aging were those related to Ni ions; the same peaks for Mn, Fe, and O remained unchanged. The changes in the Ni 2p{sub 3/2} peak may be related to: (a) the migration of Ni{sup 2+} ions from octahedral to tetrahedral sites, (b) subtle changes in the energy states of Ni{sup 2+} which promoted a more stable ionic structure, and/or (c) the presence of Ni{sup 3+} ions, some of which revert back to Ni{sup 2+}.
Date: March 1, 1995
Creator: Braski, D.N.; Osborne, N.R. & Zurbuchen, J.M.
Partner: UNT Libraries Government Documents Department

Quantitative X-ray microanalysis for the study of nanometer-scale phases in the AEM

Description: Secondary excitation can be a large source of inaccuracy in quantitative X-ray microanalysis of inhomogeneous specimens in the AEM. The size of the secondary excitation component in the measured X-ray spectrum is sensitive to the geometry of the thin foil specimen. Secondary excitation has been examined in a self-supporting disc specimen of composition NiO-20 wt.% TiO{sub 2} which has been partially masked by a gold slot washer. The ratio of the intensities of the characteristic K{sub a} peaks of Ti and Ni in X-ray spectra from a periclase-structured phase, of nominal composition NiO, has been measured to be N{sub Ti}/N{sub Ni} {approx} 0.005. There is no apparent Ti L{sub 2,3} signal in the corresponding electron energy-loss spectrum. The secondary excitation contribution to the characteristic Ti K{sub a}-peak from all sources can therefore be no larger than 0.5%. It should be possible to reduce this modest level of secondary excitation still further with a better masking arrangement.
Date: December 31, 1993
Creator: Anderson, I.M.; Bentley, J. & Carter, C.B.
Partner: UNT Libraries Government Documents Department

Optical indices of lithiated electrochromic oxides

Description: Optical indices have been determined for thin films of several electrochromic oxide materials. One of the most important materials in electrochromic devices, WO{sub 3}, was thoroughly characterized for a range of electrochromic states by sequential injection of Li ions. Another promising material, Li{sub 0.5}Ni{sub 0.5}O, was also studied in detail. Less detailed results are presented for three other common lithium-intercalating electrochromic electrode materials: V{sub 2}O{sub 5}, LiCoO{sub 2}, and CeO{sub 2}-TiO{sub 2}. The films were grown by sputtering, pulsed laser deposition (PLD) and sol-gel techniques. Measurements were made using a combination of variable-angle spectroscopy ellipsometry and spectroradiometry. The optical constants were then extracted using physical and spectral models appropriate to each material. Optical indices of the underlying transparent conductors, determined in separate studies, were fixed in the models of this work. The optical models frequently agree well with independent physical measurements of film structure, particularly surface roughness by atomic force microscopy. Inhomogeneity due to surface roughness, gradient composition, and phase separation are common in both the transparent conductors and electrochromics, resulting sometimes in particularly complex models for these materials. Complete sets of data are presented over the entire solar spectrum for a range of colored states. This data is suitable for prediction of additional optical properties such as oblique transmittance and design of complete electrochromic devices.
Date: September 1, 1996
Creator: Rubin, M.; Rottkay, K. von; Wen, S.J.; Ozer, N. & Slack, J.
Partner: UNT Libraries Government Documents Department

Sol-gel deposited electrochromic films for electrochromic smart window glass

Description: Electrochromic windows offer the ability to dynamically change the transmittance of a glazing. With the appropriate sensor and controls, this smart window can be used for energy regulation and glare control for a variety of glazing applications. The most promising are building and automotive applications. This work covers the use of sol-gel deposition processes to make active films for these windows. The sol-gel process offers a low-capital investment for the deposition of these active films. Sol-gel serves as an alternative to more expensive vacuum deposition processes. The sol-gel process utilizes solution coating followed by a hydrolysis and condensation. In this investigation the authors report on tungsten oxide and nickel oxide films made by the sol-gel process for electrochromic windows. The properties of the sol-gel films compare favorably to those of films made by other techniques. A typical laminated electrochromic window consists of two glass sheets coated with transparent conductors, which are coated with the active films. The two sheets are laminated together with an ionically conductive polymer. The range of visible transmission modulation of the tungsten oxide was 60% and for the nickel oxide was 20%. The authors used the device configuration of glass/SnO{sub 2}:F/W0{sub 3}/polymer/Li{sub Z}NiO{sub x}H{sub y}/SnO{sub 2}:F glass to test the films. The nickel oxide layer had a low level of lithiation and possibly contained a small amount of water. Lithiated oxymethylene-linked poly(ethylene oxide) was used as the laminating polymer. Commercially available SnO{sub 2}:F/glass (LOF-Tec glass) was used as the transparent conducting glass. The authors found reasonable device switching characteristics which could be used for devices.
Date: August 1, 1996
Creator: Oezer, N.; Lampert, C.M. & Rubin, M.
Partner: UNT Libraries Government Documents Department

Primary Water SCC Understanding and Characterization Through Fundamental Testing in the Vicinity of the Nickel/Nickel Oxide Phase Transition

Description: This paper quantifies the nickel alloy stress corrosion crack growth rate (SCCGR) dissolved hydrogen level functionality. SCCGR has been observed to exhibit a maximum in proximity to the nickel/nickel oxide phase transition. The dissolved hydrogen level SCCGR dependency has been quantified in a phenomenological model in terms of the stability of nickel oxide not the dissolved hydrogen level. The observed SCCGR dependency has been extended to lower temperatures through the developed model and Contact Electrical Resistance (CER) measurements of the nickel/nickel oxide phase transition. Understanding obtained from this hydrogen level SCC functionality and complementary SCC subprocesses test results is discussed. Specifically, the possible SCC fundamental subprocesses of corrosion kinetics, hydrogen permeation and pickup have also been measured for nickel alloys. Secondary Ion Mass Spectroscopy (SIMS) analysis has been performed on SCCGR specimens tested in heavy water (D{sub 2}O).
Date: May 8, 2001
Creator: Morton, D.S.; Attanasio, S.A. & Young, G.A.
Partner: UNT Libraries Government Documents Department