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  • 1
    Electronic Resource
    Electronic Resource
    Correlation of transport and magnetic critical currents in melt-processed YBa2Cu3O7−δ thick films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 1720-1725 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transport critical current measurements have been carried out on melt-processed thick films of YBa2Cu3O7−δ on yttria-stabilized zirconia in fields of up to 8 T both within grains and across grain boundaries. These measurements yield Jc values of ∼3000 A cm−2 at 4.2 K and zero magnetic field and 400 A cm−2 at 77 K and zero magnetic field, taking the entire sample width as the definitive dimension. Optical and scanning electron microscopy reveals that the thick-film grains consist typically of a central "hub'' region ∼50 μm in diameter, which is well connected to radial subgrains or "spokes'' which extend ∼1 mm to define the complete grain structure. Attempts have been made to correlate the transport measurements of inter- and intra-hub-and-spoke (H-S) critical current with values of this parameter derived previously from magnetization measurements. Analysis of the transport measurements indicates that current flow through H-S grains is constrained to paths along the spokes via the grain hub. Taking the size of the hub as the definitive dimension yields an intra-H-S grain Jc of ∼60 000 A cm−2 at 4.2 K and 0 T, which is in reasonable agreement with the magnetization data. Experiments in which the hub is removed from individual grains confirm that this feature determines critically the Jc of the film.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357687
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  • 2
    Electronic Resource
    Electronic Resource
    Investigation of the temperature dependence of the critical state in melt processed YBa2Cu3O7−∂ thick films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2067-2072 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The inter- and intra-grain critical current densities of melt processed YBa2Cu3O7−∂ (YBCO) thick films have been measured as a function of temperature using vibrating sample magnetometry. The width of the M-H hysteresis curve has been observed to scale with the cube of the sample width for temperatures up to ∼70 K and applied fields of greater than 1 T which implies that current flows on the length scale of the sample over this temperature and field regime. An exponential decrease of magnetic moment hysteresis with temperature up to ∼70 K and between ∼80 K and Tc has been observed and attributed to the dominance of inter- and intra-granular current, respectively. An empirical model is presented to account for the observed dependence of the critical current density on temperature, based upon weak link behavior within the "Hub and Spoke'' like morphology characteristic of melt processed YBCO thick films. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358847
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  • 3
    Electronic Resource
    Electronic Resource
    Investigation of the temperature dependence of the critical state in melt processed YBa2Cu3O7−∂ thick films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2607-2612 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The inter- and intra-grain critical current densities of melt processed YBa2Cu3O7−∂ (YBCO) thick films have been measured as a function of temperature using vibrating sample magnetometry. The width of the M-H hysteresis curve has been observed to scale with the cube of the sample width for temperatures up to ∼70 K and applied fields of greater than 1 T which implies that current flows on the length scale of the sample over this temperature and field regime. An exponential decrease of magnetic moment hysteresis with temperature up to ∼70 K and between ∼80 K and Tc has been observed and attributed to the dominance of inter- and intra-granular current, respectively. An empirical model is presented to account for the observed dependence of the critical current density on temperature, based upon weak link behavior within the "Hub and Spoke'' like morphology characteristic of melt processed YBCO thick films. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358724
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  • 4
    Electronic Resource
    Electronic Resource
    Investigation of the enhanced efficiencies of small superconducting loop antenna elements (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2914-2918 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fields backscattered from arrays of electrically small copper and YBCO superconducting loops are measured and compared with moment method predictions to confirm the gain enhancements and changes in Q factors due to increasing the efficiencies of the antenna elements alone, without the influence of feed and matching networks. Measurements on coplanar and parallel loop arrays show only small increases in the backscattered fields of the YBCO scatterers, with the largest increase in efficiency being for the single loop. The mutual resistance between elements reduces the benefit of adding more elements to a YBCO loop, to a greater extent than when copper elements are added to a copper loop.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354647
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  • 5
    Electronic Resource
    Electronic Resource
    Critical currents of sintered and melt-textured YBa2Cu3Ox (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2856-2858 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High critical-current densities, Jc, have been observed in single crystals and thin films of YBa2Cu3Ox. Jc in bulk materials is diappointingly low reaching a maximum in untextured material of about 103 A cm−2. The importance of raising Jc in bulk materials is paramount and most applications of bulk materials require high Jc in high magnetic fields. The work of Jin et al. in raising Jc to 17 000 A cm−2 in zero field represents a most important step in the development of bulk materials and gives real hope to bulk applications. In the communication we first describe the properties of untextured wire, and then we describe our process for melt texturing and the difficulties encountered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342726
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  • 6
    Electronic Resource
    Electronic Resource
    Microstructural and magnetization studies of sintered and melt-textured Y-Ba-Cu-O (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5930-5934 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For bulk applications, high-Tc superconductors generally require high critical current density, Jc. This paper reports two methods of producing high-Tc ceramic wires. The first is an extrusion and sintering route where Jc is routinely 600–1000 A cm−2. The second is by melt texturing or directional solidification where we have achieved in excess of 7000 A cm−2 by direct measurement at 77 K in zero field. However, the ease with which wire may be extruded and sintered is attractive and functioning devices have already been manufactured using this route. Fabrication of devices is facilitated by a unique processing route that has resulted in the strongest bulk ceramic yet reported (bend strength 〉200 MPa). The melt-texturing route and the problems associated with it are examined and compared with the extrusion and sintering route. The processing and the microstructures associated with the directionally solidified YBa2Cu3Ox will be examined in detail as will the resultant superconducting properties, in particular the magnetization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343618
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  • 7
    Electronic Resource
    Electronic Resource
    New phases in the superconducting Y:Ba:Cu:O system (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 457-459 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electron diffraction and microscopy study is presented of a variety of phases in the Y:Ba:Cu:O system in which superconductivity occurs. The superconducting phase is demonstrated by convergent beam electron diffraction to be centrosymmetric with space group Pmmm, in contrast to a previous determination of Pmm2. This discrepancy arises from local symmetry-breaking defects. In addition to this phase and a cubic BaCuO2 phase, we characterize two other phases. One is the Y-rich orthorhombic phase: Pnma with a=13.5 A(ring), b=6.3 A(ring), and c=7.6 A(ring). The second occurs by a phase transition of the superconducting Pmmm phase to P4/mmm with a=3.85 A(ring), c=11.7 A(ring). The superconducting phase may now be described as either an ordered array of oxygen vacancies in the perovskite structure, or an ordered array of oxygen interstitials in the new tetragonal phase, which may explain how the material can lose oxygen reversibly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98421
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  • 8
    Electronic Resource
    Electronic Resource
    High Q YBa2Cu3Ox cavities (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 1378-1380 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Melt-processed YBa2Cu3Ox thick film components for resonant cavities have been produced on yttria stabilized zirconica substrates. A variety of cavities have been constructed incorporating both copper and superconducting components and the TE011 modes have been examined. The highest unloaded Q factor measured was 715 688 for the TE011 mode of an all superconducting cavity at 77 K and 5.66 GHz in the Earth's magnetic field. This corresponds to a surface resistance of 1.09 mΩ over a total surface area in excess of 230 cm2. Cooling this cavity within a mumetal shield increased the unloaded Q factor by approximately 5%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107296
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  • 9
    Electronic Resource
    Electronic Resource
    Low surface resistance in YBa2Cu3Ox melt-processed thick films (1991)
    [s.l.] : Nature Publishing Group
    Nature 349 (1991), S. 680-683 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Because the of the quadratic frequency dependence of Rs in superconductors1, as opposed to the square-root dependence in normal metals, there is a great incentive to reduce Rs in superconductors so that operation of devices below the cross-over frequency benefit from a lower Rs than that of a ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/349680a0
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of chemical bonding at low temperature on the mechanical properties of an unsintered SiC compact (1987)
    Springer
    Journal of materials science 6 (1987), S. 1456-1458 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01689321
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