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in subjects: "Yttrium Oxides"

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Analysis of valence-electron structures of Y/sub 3/Al/sub 5/O/sub 12/(YAG) and Al/sub 2/O/sub 3/, Cr/sub 2/O/sub 2/ (Ruby), a study of certain properties of these laser materials related to their valence-electron structures

A direct method of determination of the valence-electron structure from its crystal structure has been presented by the writer at XIIth International Congress of Crystallography, at Ottawa, 1981. Here the method is applied to determine the valence-electron structures of Y/sub 3/Al/sub 5/O/sub 12/ (YAG) and Al/sub 2/O/sub 3/, Cr/sub 2/O/sub 3/ (ruby) to see how certain properties of these laser materials are related to their valence-electron structures. The first point observed is the very stron… more

Date: January 1, 1982

Creator: Yu, S. H. & Yu, L. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Cementitious yttria products

An investigation has been made of the physical properties and formation conditions of cements formed in the yttria/salt/water system. Cementitious binders were of the nominal Y/sub 2/(OH)/sub 5/X.H/sub 2/O type (where X represents the Cl/sup -/ or NO/sub 3//sup -/). An ammonium nitrate-produced yttria cement was shown to be sinterable and was demonstrated to form very refractory castable concretes with zirconia or alumina aggregates.

Date: March 1, 1978

Creator: Holcombe, C. E.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Theoretical modeling and experimental characterization of planar defects in Y sub 2 Ba sub 4 Cu sub 6+x O sub 14+x

Crystallographic defects and phase transformations in the system Y{sub 2}Ba{sub 4}Cu{sub 6 + x}O{sub 14 + x}(0{le}{times}{le}4) are investigated by high resolution transmission electron microscopy (TEM) and static lattice, three dimensional Monte Carlo computer simulations. High resolution images of partially transformed (x = 2 to x = 1) material reveal a prevalence of CuO planar defects (stacking faults) associated with the transformation and an absence of disturbance to the perovskite Ba-Y-Ba… more

Date: November 1, 1990

Creator: Burmester, C. P.; Fendorf, M.; Gronsky, R. & Wille, L. T.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Advanced Heat Pipe Thermionic Technology. Task I. Development of High Voltage Module. Mid-Term Status Report, May 1, 1968--February 28, 1969.

This report addresses he design of a heat pipe-thermionic module concept capable of output potentials as high as 28 volts.

Date: October 31, 1969

Creator: Longsderff, R.W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Laser deposition and laser modification of high-temperature superconducting thin films

Applications of high-temperature superconductors (HTSC) may require epitaxial films with {Tc}{ge}77 K, and J{sub c}{ge}10{sup 6} A/cm{sup 2}. In situ pulsed laser deposition (PLD) is suitable for fabrication of such films. We report parametric studies on the effect of laser and processing parameters on the crystallinity, epitaxy and electrical properties of laser-deposited HTSC thin films. In addition, several laser-based processes were used to modify the electrical properties ({Tc} and J{sub c… more

Date: January 1, 1991

Creator: Dye, R. C.; Foltyn, S. R.; Nogar, N. S.; Wu, X. D.; Peterson, E. J. & Muenchausen, R. E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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

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.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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High temperature fuel cell research and development. Final technical status report, 1 March 1979-31 March 1980. [Molten carbonate fuel cells]

The objective of the program has been to evaluate potential materials for their chemical and physical stability in molten carbonate fuel cell electrolyte. Eleven powdered candidate materials were selected based on previous physical and chemical stability tests at elevated temperatures on solid materials and/or their thermodynamic stability with respect to proposed degradation reactions. The eleven candidate materials, plus gamma lithium aluminate, were characterized prior to corrosion testing u… more

Date: May 1, 1980

Creator: Lessing, P.A.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Recent advances in high-temperature superconductor wire fabrication and applications development

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.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Electron irradiation effects in YBa/sub 2/Cu/sub 3/O/sub 7-delta/ single crystals

Defect structures in YBa/sub 2/Cu/sub 3/O/sub 7/minus/delta/ produced by electron irradiation at 300/degree/K, were investigated by transmission electron microscopy. Threshold energies for the production of visible defects were determined to b 152 keV and 131 keV (+- 7 keV) in directions near the a- and b-axes, respectively (b > a, both perpendicular to c, the long axis in the orthorhombic structure). During above-threshold irradiations in an electron flux of 3 x 10 /sup 18/ cm/sup /minus/2/s/s… more

Date: April 1, 1988

Creator: Kirk, M.A.; Baker, M.C.; Liu, J.Z.; Lam, D.J. & Weber, H.W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Preparation of oxide superconductors

Preparation of bulk superconductors by cold pressing and sintering of metal oxides has been optimized in this study. A knowledge of phase behavior was used in developing a flux method for growing superconducting single crystals of yttrium and gadolinium based superconductors. Means of achieving single-phase, high-density samples of (Rare Earth)-Ba/sub 2/Cu/sub 3/O/sub 7/ with optimal electronic properties are reviewed. 2 refs., 2 figs.

Date: January 1, 1988

Creator: Peterson, D.E.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Yttria-stabilized zirconia solid oxide electrolyte fuel cells, monolithic solid oxide fuel cells

Small cell size, thin ceramic components, and high operating temperature are the key features of the MSOFC. The small size of individual cells in the monolithic structure increases the active surface area. For example, an MSOFC with channels about 1 mm in diameter has a ratio of active surface area to volume of about 9.4 sq cm/cu cm. This is about seven times the ratio for conventional fuel cells. On this basis alone, an MSOFC with a channel diameter of 1 mm should produce the same power as a c… more

Date: January 1, 1989

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Energetics and statistics of order in alloys with application to oxide superconductors

Now that first-principles calculations of ordering transformations are becoming increasingly accurate, the deficiencies of earlier mean field methods are becoming increasingly apparent. New techniques, based on cluster expansions, are now alleviating many of the earlier problems and are producing very satisfactory results. These ideas will be illustrated for the case of oxygen ordering in the YBa{sub 2}Cu{sub 3}O{sub z} superconducting compound, for which a very simple two-dimensional Ising mod… more

Date: June 1, 1991

Creator: de Fontaine, D. (Lawrence Livermore National Lab., CA (United States) California Univ., Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering); Ceder, G. (Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Materials Science and Engineering) & Asta, M. (Lawrence Livermore National Lab., CA (United States) California Univ., Berkeley, CA (United States).

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Development, characterization and evaluation of materials for open-cycle MHD. Quarterly report for the period ending December 1980

The development and fabrication is continuing on a graded composite electrode with a refractory HfO/sub 2/-Re/sub x/O/sub y/ surface and a HfO/sub 2/-RE/sub x/O/sub y/-In/sub 2/O/sub 3/ current leadout for testing. The electrical conductivity of some oxide current leadouts were measured, and some general conclusions made regarding effects of composition. Also measured was the electrical conductivity of some yttrium chromites doped with Mg and Ca. The characterization and evaluation of Pt-coated… more

Date: January 1, 1982

Creator: Bates, J.L. & Marchant, D.D.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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YBa sub 2 Cu sub (3-x) Co sub x O sub y : A substrate material for YBCO superconductors

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)

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Neutron scattering from the flux lattice in high temperature superconductors

Neutron scattering has been used to observe diffraction from the flux-line lattice in high temperature superconductors. This technique is particularly useful in such systems as it allows observations to be made over a wide range of temperature and magnetic field. Experiments on the systems K{sub 0.4}Ba{sub 0.6}BiO{sub 3} and YBa{sub 2}Cu{sub 3}O{sub 7--8} will be described with applied magnetic fields of up to 4 Tesla and for temperatures from 2K to {Tc}.

Date: January 1, 1991

Creator: Paul, D.McK. (Warwick Univ., Coventry (United Kingdom). Dept. of Physics); Forgan, E.M.; Cubitt, R.; Lee, S.L. (Birmingham Univ. (United Kingdom)); Mook, H.A. (Oak Ridge National Lab., TN (United States)) & Timmins, P. (Institut Laue-Langevin, 38 - Grenoble (France))

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Defect structures in YBa/sub 2/Cu/sub 3/O/sub 7-x/ produced by electron irradiation

Defect structures in YBa/sub 2/Cu/sub 3/O/sub 7-x/ produced by electron irradiation at 300/sup 0/ K were investigated by transmission electron microscopy. Threshold energies for the production of visible defects were determined to be 152 keV and 131 keV (+- 7 keV) in directions near the a and b (b > a) axes (both perpendicular to c, the long axis in the orthorhombic structure), respectively. During above threshold irradiations in an electron flux of 3 x 10/sup 18/ cm/sup -2/ s/sup -1/, extended… more

Date: December 1, 1987

Creator: Kirk, M.A.; Baker, M.C.; Liu, J.Z.; Lam, D.J. & Weber, H.W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Anisotropy of oxygen tracer diffusion in YBa sub 2 Cu sub 3 O sub 7-. delta. single crystals

The crystal structure of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} strongly suggests that the diffusion of oxygen in this material will be highly anisotropic, with diffusion in the ab plane being much faster than diffusion parallel to the c axis, and this has been assumed in most analyses of diffusion in YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}. The present data confirm this hypothesis; the diffusion coefficient in the ab plane is several orders of magnitude greater than the diffusion coefficient along th… more

Date: September 1, 1989

Creator: Rothman, S. J.; Routbort, J. L.; Liu, J.-Z.; Downey, J. W.; Thompson, L. J.; Fang, Y. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Stress and phase transformation phenomena in oxide films

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.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Electron beam induced oxygen in YBa sub 2 Cu sub 3 O sub 7-x superconductors

Thin foils of bulk YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) superconductors were subjected to electron irradiation in a Transmission Electron Microscope (TEM). The resulting disordering of the oxygen atoms and vacancies in the Cu-O planes was monitored by measuring the splitting of the (110) diffraction spots in the (001) diffraction pattern. Samples were irradiated at 83K with 100, 150, 200 and 300kV electrons. The 100kV electrons did not cause any disordering, even after prolonged irradiation. Th… more

Date: January 1, 1989

Creator: Basu, S.N.; Roy, T.; Mitchell, T.E. & Nastasi, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Non-stoichiometric defects in YBaCuO thin films

Defects in superconducting YBaCuO thin films deposited by laser ablation are investigated by high resolution transmission electron microscopy. Micrographs reveal numerous defects in the YBaCuO film, falling into four basic classes. One of these is an interesting, non-stoichiometric helical defect structure which possibly corresponds to a growth-related screw dislocation. In general, defects in the YBaCuO film are associated both with growth geometry and with local deviations in stoichiometry. S… more

Date: April 1, 1991

Creator: Fendorf, M.; Tidjani, M.; 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

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EXPERIMENTAL ATTEMPTS TO STABILIZE A CUBIC FORM OF BeO

Binary mixtures of BeO with the oxides Al/sub 2/O/sub 3/, CaO, Li/sub 2/ O, MgO, Sc/sub 2/O/sub 3/, TiO/sub 2/, Y/sub 2/O/sub 3/, and ZrO/sub 2/ were fired to temperatures in excess of 2050 deg C in an attempt to produce a stabilized cubic crystalline modification of BeO. No evidence was observed in microscopic and x-ray diffraction analyses of the cooled specimens that a cubic form of BeO had formed in the experiment. (auth)

Date: December 22, 1961

Creator: Thoma, R.E.; Friedman, H.A. & McVay, T.N.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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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

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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

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Fuel cell applied research: electrocatalysis and materials. Quarterly report, January 1-March 31, 1979

In situ regeneration of surface areas of sintered carbon supported platinum electrodes in 85% H/sub 3/PO/sub 4/ at 150/sup 0/C was studied. The kinetics of oxygen reduction on platinum in trifluoromethane sulfonic acid was investigated. Overpotentials in solid oxide electrolyte fuel cells were studied. Results are presented and discussed. Also, a survey of the status of studies of phosphoric acid and molten carbonate fuel cells is described. (WHK)

Date: October 1, 1979

Creator: Srinivasan, S.; Isaacs, H. S.; McBreen, J.; O'Grady, W. E.; Olender, H.; Olmer, L. J. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department