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in subjects: "Barium Compounds"

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Computer modeling of Y-Ba-Cu-O thin film deposition and growth

The deposition and growth of epitaxial thin films of YBa{sub 2}Cu{sub 3}O{sub 7} are modeled by means of Monte Carlo simulations of the deposition and diffusion of Y, Ba, and Cu oxide particles. This complements existing experimental characterization techniques to allow the study of kinetic phenomena expected to play a dominant role in the inherently non-equilibrium thin film deposition process. Surface morphologies and defect structures obtained in the simulated films are found to closely rese… more

Date: July 1, 1991

Creator: Burmester, C.; Gronsky, R. (Lawrence Berkeley Lab., CA (United States)) & Wille, L. (Florida Atlantic Univ., Boca Raton, FL (United States). Dept. of Physics)

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Properties of epitaxial YBa sub 2 Cu sub 3 O sub 7-. delta. -based superconducting superlattices

Epitaxial YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} superconducting superlattices have been fabricated using pulsed laser deposition in which c-axis oriented YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} layers as thin as one unit cell thick are separated by relatively thick PrBa{sub 2}Cu{sub 3}O{sub 7-{delta}} based barrier layers. The superlattice {Tc} (R=0) decreases rapidly with increasing barrier layer thickness, but then saturates at a finite {Tc} for YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} layers as thin as… more

Date: September 1, 1991

Creator: Norton, D.P.; Lowndes, D.H.; Zheng, Z. Y.; Feenstra, R. (Oak Ridge National Lab., TN (United States)) & Zhu, Shen (Tennessee Univ., Knoxville, TN (United States). Dept. of Physics and Astronomy)

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Computer simulation of scattered ion and sputtered species effects in ion beam sputter-deposition of high temperature superconducting thin films

Ion beam sputter-deposition is a technique currently used by many groups to produce single and multicomponent thin films. This technique provides several advantages over other deposition methods, which include the capability for yielding higher film density, accurate stoichiometry control, and smooth surfaces. However, the relatively high kinetic energies associated with ion beam sputtering also lead to difficulties if the process is not properly controlled. Computer simulations have been perfo… more

Date: January 1, 1992

Creator: Krauss, A.R. (Argonne National Lab., IL (United States)) & Auciello, O. (Microelectronics Center of North Carolina, Research Triangle Park, NC (United States))

Item Type: Article

Partner: UNT Libraries Government Documents Department

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de Haas van Alphen effect in high temperature superconductors

The de Haas van Alphen effect has been investigated using 100 tesla fields and temperatures below 4.2 Kelvin. It is concluded from these measurements that YBCO exhibits a Fermi surface with at least three separate extremal frequencies for the c-axis parallel to the applied field. Orbital masses, renormalization g's and scattering rates are estimated from an amplitude analysis. 16 refs., 2 figs.

Date: January 1, 1991

Creator: Mueller, F.M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Extrusion of metal oxide superconducting wire, tube or ribbon

A process and apparatus for extruding a superconducting metal oxide composition YBa{sub 2}Cu{sub 3}O{sub 7-x} provides a wire (tube or ribbon) having a cohesive mass and a degree of flexibility together with enhanced electrical properties. Wire diameters in the range of 6--85 mils have been produced with smaller wires on the order of 10 mils in diameter exhibiting enhanced flexibility for forming braided, or multistrand, configurations for greater current carrying capacity. The composition for … more

Date: January 1, 1990

Creator: Dusek, J.T.

Item Type: Patent

Partner: UNT Libraries Government Documents Department

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Microstructure and properties of in-situ rf sputtered YBa sub 2 Cu sub 3 O sub 7 thin films for microwave applications

The residual surface resistance of a number of films of YBa{sub 2}Cu{sub 3}O{sub 7}, prepared by off-axis sputtering onto MgO substrates, has been measured using parallel-plate resonator technique. Deposition conditions were kept constant, apart from the substrate temperature. There is no correlation between surface resistance and other important microscopic parameters, such as T{sub c} and c-axis lattice parameter. There is, however, a trend to higher R{sub s} with increasing volume fraction o… more

Date: January 1, 1992

Creator: Reagor, D. W.; Houlton, R. J.; Garzon, F. H.; Hawley, M.; Raistrick, I. D. (Los Alamos National Lab., NM (United States)) & Piza, M. E. (Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Materials Science)

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Influence of ion beam mixing on the growth of high temperature oxide superconducting thin film

The superconducting properties of high temperature superconductor thin films are dependent on the quality of the substrate used to grow these films. In order to maximize the lattice matching between the superconducting film and the substrate, we have used a YBa{sub 2}Cu{sub 3}O{sub 7} thin film deposited on {l angle}100{r angle} SrTiO{sub 3} as a template. The first film was prepared by coevaporation of Y, BaF{sub 2} and Cu on {l angle}100{r angle} SrTiO{sub 3}, followed by an anneal in wet'' o… more

Date: January 1, 1989

Creator: Bordes, N.; Rollett, A.D.; Cohen, M.R. & Nastasi, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Cerenkov radiators for photodiodes

Several materials have been examined for use as Cerenkov converters in front of photodiodes in an effort to find a gamma detector system that has more sensitivity than a Compton detector but makes little sacrifice in bandwidth. Suprasil (fused silica) and UVT Lucite (acrylic) were 10-100 times more sensitive than a Compton detector and provided almost the same bandwidth. Barium fluoride provided almost 1000 times the sensitivity, but with a factor of 3 or 4 reduction in bandwidth. Relative sens… more

Date: January 1, 1982

Creator: Toevs, J. W.; Young, C. S.; Zagarino, P. A. & Seno, R. D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Grain boundary weak links in high- Tc superconductors

The transport critical current density (Jc) for high-{Tc} thin films, bicrystals, and bulk ceramics is shown to be determined by magnetic field penetration into the grain boundaries. The gross grain orientations may not in all cases be an important factor in determining this penetration. The parameter ({lambda}{sub G}/{lambda}{sub J}){sup 2} can characterize the strength of the grain boundary coupling, which depends mainly on the crystal coherence and connectivity at the boundary area.

Date: April 1, 1992

Creator: Shi, D.; Sengupta, S.; Goretta, K.C.; Salem-Sugui, S. Jr. (Argonne National Lab., IL (United States)); Smith, M. & Lwin, Y.N. (Western Illinois Univ., Macomb, IL (United States). Dept. of Physics)

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Analysis of barium hydroxide and calcium hydroxide slurry carbonation reactors

The removal of CO/sub 2/ from air was investigated by using a continuous-agitated-slurry carbonation reactor containing either barium hydroxide (Ba(OH)/sub 2/) or calcium hydroxide (Ca(OH)/sub 2/). Such a process would be applied to scrub /sup 14/CO/sub 2/ from stack gases at nuclear-fuel reprocessing plants. Decontamination factors were characterized for reactor conditions which could alter hydrodynamic behavior. An attempt was made to characterize reactor performance with models assuming both… more

Date: May 1, 1980

Creator: Patch, K.D.; Hart, R.P. & Schumacher, W.A.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Preparation and characterization of isotopic oxygen-enriched yttrium barium copper oxide

The preparation of labeled superconducting yttrium barium copper oxides from the labeled metal nitrates is described. The materials were characterized by a variety of physical techniques, and their superconducting properties were measured. Trends are seen in the structural parameters of the materials obtained by the nitrate route and also in isotopically enriched materials prepared via gas-phase exchange. These structural changes are accompanied by changes in superconducting properties. The /su… more

Date: January 1, 1988

Creator: Ott, K.C. & Smith, J.L.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Sintering of bulk high- Tc superconductors: Y-Ba-Cu-O

Sintering of bulk YBa{sub 2}Cu{sub 3}O{sub x} (123) samples has been conducted from 850 to 1010{degrees}C in oxygen partial pressures (P{sub O2}) of 2.5 {times} 10{sup 2} to 10{sup 5} Pa. The final grain sizes of the samples were controlled by selective use of (1) liquid phases and (2) partial decomposition of the 123 phase by sintering in a P{sub O2} that was lower than the minimum needed for 123 stability. In nearly fully dense samples, it was found that the grain size could range from about … more

Date: May 1, 1992

Creator: Goretta, K.C.; Chen, N.; Lanagan, M.T.; Wu, W.; Singh, J.P.; Olson, R.A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Electron microscopy of ceramic superconductors

The critical current Jc is at least as important as Tc (transition temperature) for applications in superconducting materials. Jc is strongly dependent on microstructure and, in consequence, electron microscopy will continue to be important in the development of practical ceramic superconductors. We will review the progress that has been made over the past year or so in studying the superconductors by electron microscopy techniques of all kinds--conventional, high resolution, analytical, etc. A… more

Date: January 1, 1988

Creator: Mitchell, T.E. & Roy, T.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Statics and kinetics of oxygen ordering in the oxide superconductor YBa sub 2 Cu sub 3 O sub z

Oxygen ordering in the high-temperature superconductor YBa{sub 2}Cu{sub 3}O{sub z} is well described by a two-dimensional Ising model with anisotropic next-nearest neighbor effective pair interactions, repulsive along the a direction, attractive along b. Monte Carlo simulation shows that this marked anisotropy gives rise, particularly at stoichiometric index z close to 7, to large deviations from unity of the ratio D{sub 11}{sup *}/D{sub 22}{sup *} of tracer diffusion tensor components in the a… more

Date: March 1, 1992

Creator: McCormack, R.; de Fontaine, D. (Lawrence Berkeley Lab., CA (United States)); Ceder, G. (Massachusetts Inst. of Tech., Cambridge, MA (United States)) & Salomons, E. (CEN Saclay, Gif-sur-Yvette, (France))

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Processing and properties of silver-clad Tl-Ba-Ca-Cu-O wires and tapes

TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} and Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} powders were synthesized, loaded into Ag tubes, and worked into wires and tapes by drawing and rolling. All processing outside of furnaces was in a dry-N{sub 2} glovebox. All heat treatments were performed in O{sub 2}. The Ag-clad wires fabricated from these powders exhibited onset of superconductivity at {approx}118 K and critical current densities at 77K of 2{times}10{sup 3} to 4{times}10{sup 3} A/cm{sup 2}. more

Date: March 1, 1992

Creator: Goretta, K.C.; Wu, C.T.; Lanagan, M.T.; Boling, M.A.; Shi, D.; Miller, D.J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Structure and flux pinning properties of irradiation defects in YBa sub 2 Cu sub 3 O sub 7-x

We review our investigations of defects produced in YBa{sub 2}Cu{sub 3}O{sub 7-x} by various forms of irradiation. The defect microstructure has been studied by transmission electron microscopy (TEM). Irradiation enhancements of flux pinning have been studied by SQUID magnetometry on single crystals. In many cases the same single crystals were used in both TEM and SQUID investigations. The primary atom recoil spectra for all the irradiations studied have been carefully calculated and used to co… more

Date: June 1, 1992

Creator: Kirk, M.A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Mechanisms of the oxidation of metals and alloys with emphasis on superconductors

Research work performed at M.I.T. under this contract has had two major thrusts. One thrust deals with the oxidation processing of, and phase transformations in, the Yb{sub n}Ba{sub 2n}Cu{sub 3n+n}O{sub x} (n = 1, 2, {infinity}) superconducting oxide system while the second thrust deals with the optimization of the properties of oxidation processed Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y}/Ag superconducting microcomposites.

Date: January 1, 1991

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Comparisons of VUU (Vlasov-Uehling-Uhlenbeck) predictions with streamer chamber data

Experimental charged particle inclusive and exclusive parameters for several nuclear systems are compared with microscopic model predictions based on the Vlasov-Uehling-Uhlenbeck equation, for various density-dependent nuclear equations of state (EOS). Inclusive variables and multiplicity distributions are in good agreement, and are not sensitive to the EOS. Rapidity spectra show evidence of being useful in determining whether the model uses the correct sections for binary collisions in the nuc… more

Date: January 1, 1987

Creator: Keane, D.; Chu, S.Y.; Fung, S.Y.; Liu, Y.M.; Qiao, L.J.; VanDalen, G. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Metal sulfite/sulfate reactions in thermochemical hydrogen cycles

The thermochemical cycles which have been most extensively developed all involve the thermal decomposition of sulfuric acid which is corrosive. Metal sulfate cycles have been studied as a means of circumventing handling corrosive mixtures at high temperatures. However, these metal sulfate cycles still use an electrochemical step to produce H/sub 2/. Alternate H/sub 2/ producing steps to be used in conjunction with metal sulfates are examined.

Date: January 1, 1980

Creator: Mason, C.F.V. & Bowman, M.G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Comparison of detector materials for time-of-flight positron tomography

Knowledge of detection efficiency and timing resolution is essential when comparing detector materials for time-of-flight positron tomography. We present results of Monte Carlo calculations of the detection efficiency of plastic, lead loaded plastic, NaI(T1), liquid xenon, bismuth germanate (BGO), CsF, BaF/sub 2/, Ge, and HgI/sub 2/ for 511 keV photons. We also use recently published values of timing resolution for these detector materials to tabulate the quantity (efficiency)/sup 2//(time reso… more

Date: June 1, 1982

Creator: Derenzo, S.E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Characterization of internal boundary layer capacitors

Internal boundary layer capacitors were characterized by scanning transmission electron microscopy and by microscale electrical measurements. Data are given for the chemical and physical characteristics of the individual grains and boundaries, and their associated electric and dielectric properties. Segregated internal boundary layers were identified with resistivities of 10/sup 12/-10/sup 13/ ..cap omega..-cm. Bulk apparent dielectric constants were 10,000-60,000. A model is proposed to explai… more

Date: May 1, 1980

Creator: Park, H. D. & Payne, D. A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Hydrides and Metal-Hydrogen Systems. Final Report

The work reported deals with the preparation and physical properties, especially thermal dissociation pressures, and densities of hydrides, hydrogen- metal systems, and mixtures of hydrides with other substances. Possible applicatlons as moderators, high-temperature neutron shields, and low-temperature shields are cited and design problems discussed. Most of the data on dissociation pressures cover ranges and compounds not hltherto explored because of experimental difficulties and the basic kno… more

Date: April 30, 1951

Creator: Gibb, T. R. P., Jr.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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The influence of the substrate surface on the nucleation and growth of superconducting thin films

The quality of epitaxially grown superconducting thin films is dependent on the nature of the substrate surface. In this study, the surface of <100> oriented SrTiO{sub 3} single crystals was modified by mechanical polishing, thermal annealing and chemical etching. A study of the YBa{sub 2}Cu{sub 3}O{sub 7-x} thin films grown on these substrates showed that high quality superconducting films were obtained when the substrate surface was highly oriented in the <100> direction and was also microsco… more

Date: January 1, 1989

Creator: Basu, S.N.; Bordes, N.; Rollett, A.D.; Cohen, M.R. & Nastasi, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Some reduced ternary and quaternary oxides of molybdenum containing strong metal-metal bonds. [Molybdates of ScZn, LiZn, Zn, Ba, and Na]

ScZnMo/sub 3/O/sub 8/, LiZn/sub 2/Mo/sub 3/O/sub 8/, and Zn/sub 3/Mo/sub 3/O/sub 8/ were synthesized and crystal structures were determined for the latter two. These oxides contain the same type of triangular molybdenum atom clusters found in Zn/sub 2/Mo/sub 3/O/sub 8/, but each of the trimeric clusters has available one or two additional electrons for participation in metal-metal bonding. Another new ternary oxide containing discrete metal atom clusters is Ba/sub 1/ /sub 14/Mo/sub 8/O/sub 16/.… more

Date: October 1, 1981

Creator: Torardi, C.C.

Item Type: Report

Partner: UNT Libraries Government Documents Department