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The influence of anharmonic phonons on the isotope effect in high- Tc oxides

Description: Anharmonic phonons are examined to study the unusual isotope effect exponents for the high-{Tc} oxides. Within a simple model of anharmonicity, the mass dependences of the electron-phonon coupling constant {lambda} and the phonon frequency determine the isotope effect exponent {alpha} as a function of coupling strength. A model in which the outer wells of a multiple-well potential deepen as the orthorhombic/low temperature tetragonal phase transition in La{sub 2-x}M{sub x}CuO{sub 4} is approach… more
Date: January 1, 1992
Creator: Crespi, V.H. & Cohen, M.L.
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Recent advances in high-temperature superconductor wire fabrication and applications development

Description: In this paper, recent advances in fabrication of HTS wires are summarized, and detailed discussion is provided for developments in near- and intermediate-term applications. Near-term applications, using presently obtainable current densities, include: liquid-nitrogen depth sensors, cryostat current leads, and magnetic bearings. Intermediate-term applications, using current densities expected to be available in the near future include fault-current limiters and short transmission lines. 25 refs.
Date: January 1, 1992
Creator: Hull, J.R. & Uherka, K.L.
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YBa sub 2 Cu sub (3-x) Co sub x O sub y : A substrate material for YBCO superconductors

Description: The physical properties of the ceramic YBa{sub 2}Cu{sub (3-x)}Co{sub x}O{sub y} have been investigated in order to evaluate its usefulness as a substrate material for YBCO superconductors. YBa{sub 2}Cu{sub (3-x)}Co{sub x}O{sub y} has been found to be thermally and chemically compatible with 123 and displays adequate electrical properties for a substrate material. A material with the nominal composition of YBa{sub 2}Cu{sub 2.2}Co{sub 0.8}O{sub 7} was investigated, extensively. The mechanical pro… more
Date: April 1, 1992
Creator: Vienna, J.D.; Balachandran, U.; Poeppel, R.B. (Argonne National Lab., IL (United States)); Cermignani, W. & Taylor, J.A. (State Univ. of New York, Alfred, NY (United States). Coll. of Ceramics)
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Stress and phase transformation phenomena in oxide films

Description: In situ optical methods are reviewed for characterization of phase transformation processes and evaluation of residual stress in solution- deposited metastable oxide films. Such low density films most often are deposited as disordered phases making them prone to crystallization and attendant densification when subjected to increased temperature and/or applied pressure. Inherent stress imparted during film deposition and its evolution during the transformation are evaluated from phonon frequency… more
Date: April 1, 1992
Creator: Exarhos, G.J. & Hess, N.J.
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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

Description: 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)
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Grain boundary weak links in high- Tc superconductors

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

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

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

Description: 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.
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Fine scale mesostructures in superconducting and other materials

Description: We review experimental and theoretical literature on mesoscale features and structures in a variety of displacively transforming materials. These include twinning in martensites and the much finer scale tweed; both may have significant effects on both normal and superconducting properties. Elastic properties are particularly strongly affected. Recent x-ray neutron experiments suggest them in hi-{Tc} materials.
Date: January 1, 1992
Creator: Krumhansl, J.A.
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Oxygen ordering and strain-related morphology in YBa sub 2 Cu sub 3- x O sub 7 systems

Description: Monte Carlo simulations were performed on an anisotropic lattice gas model which represent well the interactions between oxygen atoms in YBa{sub 2}Cu{sub 3}O{sub 7} systems doped with trivalent impurity atoms M such as Fe or Al. Concentration wave amplitudes obtained from these simulations were used to calculate the diffuse X-ray scattering intensity caused by the resulting displacement field using a concentration wave/displacement wave approach, and the results are compared with X-ray and elec… more
Date: January 1, 1992
Creator: Cha, Zhi-Xiong; Zhu, Yimei & Welch, D.O.
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Superconducting materials

Description: Our research on high temperatures superconductors has produced novel insights for the normal state properties of copper oxides that have been discovered in the last few years. Advances in materials preparation have produced singly crystal samples, and sophisticated surface cleavage techniques have unveiled truly metallic behavior in many respects. Thus, the recent confirmation of a Fermi surface in several cuprate superconductors by photoemission spectroscopy has aroused interest in experimenta… more
Date: January 1, 1992
Creator: Ruvalds, J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Influence of oxygen partial pressure and silver additions on microstructure and related properties of YBCO superconductors

Description: Microstructure has a great influence on the mechanical and superconducting properties of YBCO. Mechanical properties of YBCO can be improved by both modifying the monolithic microstructure and developing composites of YBCO with silver (Ag). When monolithic YBCO was sintered to high densities ({approx} 91%) at a relatively low temperature ({approx} 910{degrees}C) by controlling oxygen partial pressure during sintering, the result was a small-grain microstructure (average grain size {approx} 5 {m… more
Date: February 1, 1992
Creator: Singh, J.P.; Joo, J.; Guttschow, R. & Poeppel, R.B.
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Flux dynamics and irreversibility in YBa sub 2 Cu sub 3 O sub 7 with Y sub 2 BaCuO sub 5 inclusions and in single crystal YBa sub 2 Cu sub 3 O sub 7

Description: We have measured the ac magnetic permeability response function {mu} = {mu}{prime} + i{mu}{double prime} in melt-processed melt grown YBa{sub 2}Cu{sub 3}O{sub 7} with Y{sub 2}BaCuO{sub 5} inclusions (MPMG) and in single crystal YBa{sub 2}Cu{sub 3}O{sub 7} (SC) in applied magnetic fields up to 8 Tesla oriented either parallel or perpendicular to the crystalline c-axis. The ac response of the two samples has been mapped out as a function of temperature, frequency, ac field amplitude, dc applied f… more
Date: January 1, 1992
Creator: Fossheim, K.; Karkut, M.G.; Heill, L.K.; Slaski, M.; Sagdahl, L.T. (Norges Tekniske Hoegskole, Trondheim (Norway). Div. of Physics Selskapet for Industriell og Teknisk Forskning, Trondheim (Norway)); Vinokur, V. (Argonne National Lab., IL (United States)) et al.
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Oxygen permeability of several ceramic oxides above 1200 degrees C

Description: Oxygen permeability as a function of temperature was measured for several ceramic oxides over the range 1200 to 1700{degrees}C. Of the oxides testbed, alumina, beryllia, yttria, lanthanum halfnate, and calcium zironcate exhibited the lowest permeabilities in order of decreasing resistance to oxygen transport. None of the permeability constants were less than the 10{sup {minus}10} to 10{sup {minus}12} g O{sub 2}/cm {center dot} s needed for a useful protective coating system above 1500{degrees}C… more
Date: January 1, 1992
Creator: Courtright, E.L. & Prater, J.T.
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Electronic transport and mixed conductivity in perovskite type oxides

Description: The goal of the investigation presented in this report is to study the inter-relationship between electrical conductivity, oxidation-reduction kinetics, defect structure, and composition of n- and p-type binary and ternary transition metal oxides. The experimental part of the investigation included specimen preparation, thermogravimetric measurements, X-ray diffraction, thermally stimulated current, DTA/TGA, optical absorption, transmission electron microscopy, electrical conductivity, and Seeb… more
Date: March 3, 1992
Creator: Anderson, H. U.; Nasrallah, M. M.; Sparlin, D. M. & Parris, P. E.
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NQR investigation of pressure-induced charge transfer in oxygen-deficient YBa sub 2 Cu sub 3 O sub 7-. delta. (. delta. = 0. 38)

Description: Measurements of the pressure dependence of {sup 63}Cu nuclear quadrupole frequency in YBa{sub 2}Cu{sub 3}O{sub 6.62} from ambient pressure up to 1.5 GPa at 4k have been performed. {Tc} was found to increase with pressure: d{Tc}/dp {approximately} 5 K/GPa. All observed NQR lines are linear in pressure: dln{nu}{sub Q}/dp=z. We found positive z for the empty chain sites, consistent with ionic (Cu{sup 1+}) configuration in which the atom simply feels a squeezing lattice. Planar coppers close to the… more
Date: January 1, 1992
Creator: Reyes, A. P.; Ahrens, E. T.; Hammel, P. C.; Heffner, R. H. (Los Alamos National Lab., NM (United States)) & Takigawa, M. (International Business Machines Corp., Yorktown Heights, NY (United States). Thomas J. Watson Research Center)
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Recent Results in Characterization of Melt-Grown and Quench-Melt- Grown YBCO Superconductors

Description: From the standpoint of applications, melt-grown (MG) and quench-melt-grown (QMG) bulk YBCO superconductors are of considerable interest. In this paper, we studied the intragranular critical current density (J{sub c}), the apparent pinning potential (U{sub o}), and the irreversibility temperature (T{sub irr}) of MG and QMG samples and compared the results to those for conventionally sintered YBCO. A systematic increase in U{sub o} and a slower drop in J{sub c} with temperature indicate a systema… more
Date: February 1, 1992
Creator: Balachandran, U.; Poeppel, R. B. & Gangopadhyay, A. K.
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Zirconia-based fuel cells for power generation

Description: This paper reviews the design and operation of the high temperature solid oxide fuel cells based on yttria-stabilized zirconia electrolyte. The functional requirements of the various cell components are presented; and the materials and fabrication processes used for different cell components are described. Finally, the recent progress made toward commercialization of these cells for clean and efficient power generation is discussed.
Date: January 1, 1992
Creator: Singhal, S.C.
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High-temperature superconductor applications development at Argonne National Laboratory

Description: Developments at Argonne National Laboratory of near and intermediate term applications using high-temperature superconductors are discussed. Near-term applications of liquid-nitrogen depth sensors, current leads, and magnetic bearings are discussed in detail.
Date: February 9, 1992
Creator: Hull, J.R. & Poeppel, R.B.
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The variability residual stresses of thick superconductor films during orthorhombic to tetragonal transformation

Description: YBa{sub 2}Cu{sub 3}O{sub x} thick films have been deposited by spray pyrolysis of a sol-gel on 10 cm diameter polycrystalline MgO wafers. The film thickness was built up in layers of approximately 1 {mu}m thick. The in-plane residual stresses were measured by an optical interferometry (shadow moire) method as a function of film structure. In-plane residual stress maps over the area of the wafer have been obtained. The average stress of the 5 {mu}m orthorhombic phase was 0.84 GPa. As the film tr… more
Date: January 1, 1992
Creator: Wu, W.; Danyluk, S. (Illinois Univ., Chicago, IL (United States). Dept. of Civil Engineering, Mechanics, and Metallurgy); Lanagan, M.T. & Poeppel, R.B. (Argonne National Lab., IL (United States))
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Material development in the SI sub 3 N sub 4 system using glass encapsulated Hip'ing

Description: This report covers a two-year program to develop fully dense Si{sub 3}N{sub 4} matrix SiC whisker composites with enhanced properties over monolithic Si{sub 3}N{sub 4} materials. The primary goal was to develop a composite with a fracture toughness > 10 MPa{radical}m, capable of using high pressure glass encapsulated HIP'ing. Coating methods were developed to apply thin (<150nm) stoichiometric BN layers to SiC whiskers and also to apply a dual coating of SiC over carbon to the whiskers. Fractur… more
Date: April 1, 1992
Creator: Corbin, N. D.; Sundberg, G. J.; Siebein, K. N.; Willkens, C. A.; Pujari, V. K.; Rossi, G. A. et al.
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Sol-gel preparation of ion-conducting ceramics for use in thin films. [LaSrCoO[sub 3]; SrCeY[sub x]O[sub 3]]

Description: A metal alkoxide sol-gel solution suitable for depositing a thin film of La[sub 0.6]Sr[sub 0.4]CoO[sub 3] on a porous substrate has been developed; such films should be useful in fuel cell electrode and oxygen separation membrane manufacture. Crack-free films have been deposited on both dense and porous substrates by dip-coating and spin-coating techniques followed by a heat treatment in air. Fourier transform infrared spectroscopy was used to determine the chemical structure of metal alkoxide … more
Date: December 1, 1992
Creator: Steinhauser, M.I.
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A theoretical analysis of the effect of uniaxial elastic strain on the critical temperature of cuprate superconductors

Description: Factors which influence the effect of uniaxial stress and strain on the superconducting critical temperature are discussed, with emphasis on the effect of uniaxial strain on the mobile hole density of YBa[sub 2]Ci[sub 3]O[sub 7].
Date: January 1, 1992
Creator: Welch, D.O. (Brookhaven National Lab., Upton, NY (United States)) & Baetzold, R.C. (Corporate Research Laboratories, Eastman Kodak Co, Rochester, NY (United States))
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