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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

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

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

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

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

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

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

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
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

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

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

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

Corrosion of cermet anodes during low temperature electrolysis of alumina. Final report

Description: Successful development of inert anodes to replace carbon anodes in Hall cells has the potential benefits of lower energy consumption,lower operating costs, and reduced CO{sub 2} and CO emissions. Using inert anodes at reduced current density and reduced operating temperature (800 C) has potential for decreasing the corrosion rate of inert anodes. It may also permit the use of new materials for containment and insulation. This report describes the fabrication characteristics and the corrosion performance of 5324-17% Cu Cermet anodes in 100 hour tests. Although some good results were achieved, the corrosion rate at low temperature (800 C) is varied and not significantly lower than typical results at high temperature ({approximately} 960 C). This report also describes several attempts at 200 hour tests, with one anode achieving 177 hours of continuous operation and another achieving a total of 235 hours but requiring three separate tests of the same anode. The longest run did show a lower wear rate in the last test; but a high resistance layer developed on the anode surface and forced an unacceptably low current density. It is recommended that intermediate temperatures be explored as a more optimal environment for inert anodes. Other electrolyte chemistries and anode compositions (especially high conductivity anodes) should be considered to alleviate problems associated with lower temperature operation.
Date: September 26, 1997
Creator: Kozarek, R.L.; Ray, S.P.; Dawless, R.K. & LaCamera, A.F.
Partner: UNT Libraries Government Documents Department

The Influence of Dissolved hydrogen on Nickel Alloy SCC: A Window to Fundamental Insight

Description: Prior stress corrosion crack growth rate (SCCGR) testing of nickel alloys as a function of the aqueous hydrogen concentration (i.e., the concentration of hydrogen dissolved in the water) has identified different functionalities at 338 and 360 C. These SCCGR dependencies have been uniquely explained in terms of the stability of nickel oxide. The present work evaluates whether the influence of aqueous hydrogen concentration on SCCGR is fundamentally due to effects on hydrogen absorption and/or corrosion kinetics. Hydrogen permeation tests were conducted to measure hydrogen pickup in and transport through the metal. Repassivation tests were performed in an attempt to quantify the corrosion kinetics. The aqueous hydrogen concentration dependency of these fundamental parameters (hydrogen permeation, repassivation) has been used to qualitatively evaluate the film-rupture/oxidation (FRO) and hydrogen assisted cracking (HAC) SCC mechanisms. This paper discusses the conditions that must be imposed upon these mechanisms to describe the known nickel alloy SCCGR aqueous hydrogen concentration functionality. Specifically, the buildup of hydrogen within Alloy 600 (measured through permeability) does not exhibit the same functionality as SCC with respect to the aqueous hydrogen concentration. This result implies that if HAC is the dominant SCC mechanism, then corrosion at isolated active path regions (i.e., surface initiation sites or cracks) must be the source of localized elevated detrimental hydrogen. Repassivation tests showed little temperature sensitivity over the range of 204 to 360 C. This result implies that for either the FRO or the HAC mechanism, corrosion processes (e.g., at a crack tip, in the crack wake, or on surfaces external to the crack) cannot by themselves explain the strong temperature dependence of nickel alloy SCC.
Date: October 12, 2000
Creator: Morton, D.S.; Attanasio, S.A.; Young, G.A.; Andresen, P.L. & Angeliu, T.M.
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

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