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Oxygen stoichiometry and its influence on superconductivity in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}

Description: Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} (2212) was synthesized from freeze-dried precursors. The oxygen content of 2212 was determined as a function of temperature and oxygen partial pressure and the variation of Tc with oxygen content was determined. It was found that 2212 without excess oxygen (x = 0) is superconducting. This points to the role of the (Bi-O){sub {infinity}} layers as a source for holes in 2212. Four probe resistivity measurements were also performed on 2212. The nature of oxy… more
Date: December 31, 1994
Creator: Krishnaraj, P.; Lelovic, M.; Eror, N. G. & Balachandran, U.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Neutron scattering studies of magnetism in the high-Tc materials

Description: In this paper, I shall attempt to review what has been learned about magnetism in the high-{Tc} family of compounds using neutron scattering techniques. Whether or not it is true that magnetic effects are involved in an essential way in the mechanism for superconductivity in these materials (a point which has not yet been firmly established), they offer fascinating examples for the study of magnetism for its own sake, being realizations of spin {1/2} 2D quantum antiferromagnets. Further, the ra… more
Date: December 31, 1990
Creator: Sinha, S. K.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Technology development for iron Fischer-Tropsch catalysts. Technical progress report No. 8, July 1, 1992--September 30, 1992

Description: The objectives of this contract are to develop a technology for the production of active and stable iron Fischer-Tropsch catalysts for use in slurry-phase synthesis reactors and to develop a scaleup procedure for large-scale synthesis of such catalysts for process development and long-term testing in slurry bubble-column reactors. With a feed containing hydrogen and carbon monoxide in the molar ratio of 0.5 to 1.0 to the slurry bubble-column reactor, the catalyst performance target is 88% CO + … more
Date: December 31, 1992
Creator: Frame, R. R. & Gala, H. B.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Development of novel copper-based sorbents for hot-gas cleanup. Final technical report, September 1, 1991--August 31, 1992

Description: The objective of this investigation was to evaluate several novel copper-based binary oxides for their suitability as regenerable sorbents for hot gas cleanup application in the temperature range of 650{degree} to 850{degree}C. To achieve this objective, several novel binary oxides of copper were systematically evaluated and ranked in terms of their high-temperature stability against reduction to metal, sulfidation reactivity, and regenerability. The sorbents studied included oxides of chromium… more
Date: December 31, 1992
Creator: Abbasian, J.; Hill, A. H.; Wangerow, J. R.; Flytzani-Stephanopoulos, M.; Bo, Luhong; Patel, C. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Aspects of macroscopic phase separation and interstitial oxygen ordering in oxygen doped La{sub 2}CuO{sub 4+{delta}}

Description: NMR and neutron diffraction measurements reveal that macroscopic phase separation and the tetragonal to orthorhombic (TO) structural phase coincide at two distinct points in the temperature-doping phase plot for oxygen doped La{sub 2}CuO{sub 4+{delta}}. Thus the TO phase line coincides with the phase separation line. This is evidence that the macroscopic phase separation is inhibited in the tetragonal phase. We propose that the interstitial oxygen has higher mobility in the orthorhombic phase a… more
Date: December 31, 1994
Creator: Hammel, P. C.; Fisk, Z.; Statt, B. W.; Chou, F. C.; Johnston, D. C.; Cheong, S. W. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Infrared properties of high T{sub c} superconductors

Description: Over the past several years a coherent phenomenology of the high {Tc} cuprate superconductors has begun to emerge. Infrared measurements have contributed several important ingredients to this picture including: (1) the inference of a scattering rate that is linear in frequency for {omega}>T, and of order {omega}, (2) a characteristic energy scale in the superconducting state of 500 cm{sup {minus}1} (60 meV), which can be interpreted as a superconducting pair excitation threshold or energy gap, … more
Date: December 31, 1991
Creator: Schlesinger, Z.; Rotter, L. D.; Collins, R. T.; Holtzberg, F.; Feild, C.; Welp, U. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Ac losses in YBa{sub 2}Cu{sub 3}O{sub 7} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Ci{sub 3}O{sub 10} superconductors at power frequencies

Description: Ac losses of sintered and melt-textured YBa{sub 2}Cu{sub 3}O{sub 7} bars and powder-in-a-tube processed Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} tapes were measured at 4.2, 65, 70 and 77 K and at 15--180 Hz. In general, the results are well described by the critical state model for the ac losses. However, the losses for the Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} tapes at 4.2 K exhibited significant contributions from the eddy currents in the Ag sheath.
Date: December 31, 1991
Creator: Orehotsky, J.; Reilly, K. M.; Suenaga, M.; Hikata, T.; Ueyama, M. & Sato, K.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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TEM study of flux pinning defects in YBa{sub 2}Cu{sub 3}O{sub 7- {delta}} produced by 580 MeV Sn ion irradiation

Description: Recent studies of high {Tc} superconductors irradiated with high energy heavy ions have indicated that a defect structure is produced which is extremely effective in pinning magnetic flux lines. In attempting to develop models to account for these observations, it is imperative to have a complete characterization of the defects responsible for the property enhancements. Hence, the defect microstructure produced in single crystal YBCO by 580 MeV Sn{sup 30+} irradiation, recently demonstrated to … more
Date: December 31, 1991
Creator: Wheeler, R.; Kirk, M. A.; Brown, R.; Marwick, A. D.; Civale, L. & Holtzberg, F. H.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Synthesis and properties of new family of superconducting copper oxides based on GaO layers

Description: We have discovered the first layered superconducting copper oxide with small, fixed oxidation state cations separating the conducting CuO{sub 2} planes. This material, GaSr{sub 2}Y{sub 1-x}Ca{sub x}Cu{sub 2}O{sub 7}, is similar to YBa{sub 2}Cu{sub 3}O{sub 7} with the square planar copper chains replaced by chains of edge-shared GaO{sub 4} tetrahedra. Thus, oxidation can occur only for the copper ion located in square pyramidal coordination in the CuO{sub 2} plane. The undoped parent compound, x… more
Date: December 31, 1991
Creator: Dabrowski, B.; Zhang-McCoy, V.; Radaelli, P.; Mitchell, A. W.; Hinks, D. G.; Vaughey, J. T. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Preparation of high quality YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} thick films on flexible Ni-based alloy substrates with textured buffer layers

Description: High current YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) thick films on flexible nickel substrates with textured buffer layers were deposited by using ion beam assisted deposition (IBAD). Pulsed laser deposited YBCO films were not only c-axis oriented with respect to the film surface but also strongly in-plane textured. The in-plane mosaic spread of YBCO films was {approximately} 10{degrees}. A critical current density of 8x10{sup 5} A/cm{sup 2} was obtained at 75 K and zero field for thin YBCO … more
Date: December 31, 1995
Creator: Wu, X. D.; Foltyn, S. R.; Arendt, P.; Townsend, J.; Campbell, I. H.; Tiwari, P. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Explosively produced megagauss fields and recent solid state applications

Description: Large magnetic fields may be generated by compression of an initial magnetic flux generated over a large area at relatively low magnetic field into a region of smaller area. Following a discussion of flux compression principles, the authors discuss megagauss field systems in use at Los Alamos where chemical explosives are used to compress the flux. Their use in some solid state experiments will be discussed briefly, including a planned set of experiments on YBCO to be done jointly with a Russia… more
Date: December 31, 1993
Creator: Fowler, C. M.; Freeman, B. L.; Hults, W. L.; King, J. C.; Mueller, F. M.; Rickel, D. G. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Flux pinning by heavy-ion-irradiation induced linear defects in YBa{sub 2}Cu{sub 3}O{sub 7} epitaxial films

Description: We report some transport measurements carried out to study flux pinning by heavy-ion-irradiation induced linear defects in Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} films. Our results show that in these in situ deposited films containing a large concentration of defects frozen-in at the time of film growth, a marginal enhancement in critical current density occurs when the density of linear defects < 5 {times} 10{sup 10}/cm{sup 2}, and their diameter of the order of coherence length. This criterion is… more
Date: December 31, 1992
Creator: Budhani, R. C.; Zhu, Y. & Suenaga, M.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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[Surface studies of absorbents for the removal of SO{sub x} and NO{sub x}]. Quarterly report, September 1--November 30, 1988

Description: Work this quarter was devoted to initiating the coordinated experimental and theoretical/computational modeling study of CuO dispersed on alumina for adsorption of sulfur oxide gases. Research was devoted to characterizing CuO itself, as well as sulfur model compounds for benchmark comparisons, and toward modeling of copper site locations for dispersion on alumina.
Date: December 31, 1988
Creator: Cooper, B. R. & Montano, P. A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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A high-efficiency thermoelectric converter for space applications

Description: This paper presents a concept for using high-temperature superconducting materials in thermoelectric generators (SCTE) to produce electricity at conversion efficiencies approaching 50% of the Carrot efficiency. The SCTE generator is applicable to systems operating in temperature ranges of high-temperature superconducting materials and thus would be a low-grade converter. Operating in cryogenic temperature ranges provides the advantage of inherently increasing the limits of the Carrot efficiency… more
Date: December 31, 1990
Creator: Metzger, J. D. & El-Genk, M. S.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Development of high temperature superconductors for magnetic field applications

Description: The key requirement for magnetic field applications of high temperature superconductor (HTS) materials is to have conductors with high transport critical current density available for magnet builders. After 3 or 4 years of being without any such object, conductor makers have had recent success in producing simple conductor prototypes. These have permitted the construction of simple HTS magnets having self fields exceeding 1 tesla at 4K. Thus the scientific feasibility of making powerful HTS mag… more
Date: December 31, 1991
Creator: Larbalestier, D. C.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Mechanisms of the oxidation of metals and alloys with emphasis on superconductors. A report for the period beginning December 1, 1990

Description: 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: December 31, 1991
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Development of novel copper-based sorbents for hot-gas cleanup. Final technical report, 1 September 1992--31 August, 1993

Description: The objective of this investigation is to evaluate two novel copper-based sorbents, namely Cu-Cr and Cu-Ce, for their effectiveness in removing hydrogen sulfide from fuel gas in the temperature range of 650 to 850 C. Such high temperatures will be required for the new generation of gas turbines in Integrated Gasification Combined Cycle systems. Structural and kinetic studies were conducted on various compositions of the two Cu-based sorbents to determine the optimum sorbent composition. The eff… more
Date: December 31, 1993
Creator: Hill, A. H.; Abbasian, J. & Flytzani-Stephanopoulos, M.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Technology development for iron Fischer-Tropsch catalysts. Technical progress report No. 4, June 26, 1991--September 26, 1991

Description: Objectives are to develop active, stable iron Fischer-Tropsch catalysts for use in slurry-phase synthesis reactors and to develop a scaleup procedure for large-scale synthesis of such catalysts for process development and long-term testing in slurry bubble-column reactors. For a H{sub 2}-CO in molar ratio of 0.5 to 1.0, catalyst performance target is 88% CO+H{sub 2} conversion at a minimum space velocity of 2.4 NL/hr/gFe, with no more than 4% methane/ethane selectivity and 1% conversion loss pe… more
Date: December 31, 1991
Creator: Frame, R. R.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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[Surface studies of absorbents for the removal of SO{sub x} and NO{sub x}]. Quarterly report, December 1, 1988--February 28, 1989

Description: During this quarter we studied the X-ray absorption spectra of copper oxides compounds exposed to flue gases. Model compounds were used as standards for our sorbents. We also continued growing CuO single crystals using a variety of approaches; the first samples obtained were too small to be of any use (1 mm). The EELS measurements were continued on the CuO sorbents. The spectra of oxidized Cu(100) were measured over a wide range of coverage and temperature. We measured in situ the Cu K-edge abs… more
Date: December 31, 1989
Creator: Cooper, B. R. & Montano, P. A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Lattice instabilities and structural phase transformations in La{sub 2}CuO{sub 4} superconductors and insulators

Description: Soft-mode structural phase transformations, common in many perovskite-based materials, are also found in La{sub 2}CuO{sub 4} and structurally related oxides. The resulting phase behavior is rather complex, but is a natural consequence of the degeneracy of the soft phonon order parameters. This paper reviews the structural and lattice-dynamical results and their interpretation based upon mean-field statistical mechanical models.
Date: December 31, 1991
Creator: Axe, J. D.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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[Surface study of absorbents for the removal of SO{sub x} and NO{sub x}]. Quarterly report, June 1, 1990--August 31, 1990

Description: XANES and EXAFS measurements were made on a CuO/Al{sub 2}O{sub 3} sample which went through a complete reaction cycle with flue gases, followed by comparison with pure CuO. In the modeling studies, of the possible bridging type adsorption configurations for the SO{sub 2} molecule on CuO/Al{sub 2}O{sub 3}, the only one yielding SO{sub 2} adsorption of possible practical interest is that for the SO{sub 2} molecule bridging a Cu and an Al atom with the molecule bent away from the surface; the bond… more
Date: December 31, 1990
Creator: Cooper, B. R. & Montano, P.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Extrusion of metal oxide superconducting wire, tube or ribbon

Description: 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: December 31, 1990
Creator: Dusek, Joseph T.
Item Type: Refine your search to only Patent
Partner: UNT Libraries Government Documents Department
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[Surface study of absorbents for the removal of SO{sub x} and NO{sub x}]. Quarterly report, September 1, 1990--November 30, 1990

Description: XANES spectra are given for a number of model sulfur-containing compounds. The XANES and EXAFS spectra and structures of the inorganic standards (CuSO{sub 4}, FeS{sub 2}, FeS, CuS) are discussed. Calculations were made on SO{sub 2} adsorption on CuO/Al{sub 2}O{sub 3} surface; results show that the SO{sub 2} is adsorbed on the surface via O-Cu bonding, probably in the form of a ``bridge`` with the two oxygen atoms of SO{sub 2}sitting at two surface metal atoms. It is probably better to have low-… more
Date: December 31, 1990
Creator: Cooper, B. R. & Montano, P.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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[Surface studies of absorbents for the removal of SO{sub x} and NO{sub x}]. Quarterly report, June 1, 1989--August 31, 1989

Description: During this quarter, we continued to study the X-ray absorption spectra of copper oxide sorbents exposed to flue gases as a function of temperature. Our purpose was to investigate in more detail the transformation occurring above 200 C. We report here a series of in situ EXAFS and XANES measurements for CuO/A{sub 2}O{sub 3} sorbents and model compounds. We investigated the evolution of the structure at the Cu site as a function of temperature in the presence or absence of flue gases. Below we d… more
Date: December 31, 1989
Creator: Cooper, B. R. & Montano, P. A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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