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  • 1
    Electronic Resource
    Electronic Resource
    Millimeter wave surface resistance of grain-aligned Y1Ba2Cu3Ox bulk material (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 874-879 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report measurements of the millimeter wave surface resistance of grain-aligned YBa2Cu3Ox bulk material grown by a liquid phase process. The measurements were performed by replacing the endplate of a TE011 cylindrical copper cavity with the superconducting sample. Surface resistance was measured for samples with surfaces oriented perpendicular and parallel to the c-axis of the grains. We show that, for the parallel configuration, the surface resistance at 77 K and 80 GHz is typically near 100 mΩ. For a very well-aligned sample with a very low density of Y2BaCuOy precipitates, measured in the perpendicular configuration, the transition width (10%–90%) is about 2 K and the surface resistance is less than 50 mΩ at 88 K. The effect of microstructure on surface resistance is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347326
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic levitation and stiffness in melt-textured Y-Ba-Cu-O (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2089-2091 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic levitation and stiffness have been measured in several systems composed of a permanent magnet elastically suspended above a stationary melt-textured sample of Y-Ba-Cu-O. The levitation force and vertical stiffness have been calculated on the basis of magnetization measurements of the same system, and the calculated results showed excellent agreement with the experimental measurements. Based on the force and magnetization measurements, it is predicted that the same Y-Ba-Cu-O material configured in a geometry suitable for magnetic bearings could produce a levitation pressure of 100–400 kPa at 20 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351595
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic field and temperature dependence of flux creep in oriented grained and single-crystalline YBa2Cu3Ox (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3498-3503 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermally activated flux creep of oriented grained and single-crystalline YBa2Cu3Ox was studied in fields up to 12 T and at temperatures ranging between 4 and 90 K. In fixed fields the activation energy U0 of both samples was found to increase with temperature, pass through some maximum and drop to the order of kBT around the irreversibility line. While at constant temperature U0 of the oriented grained sample showed a monotonous decrease with field; in the case of the single crystal it was found to follow a characteristic minimum-maximum structure paralleled by the previously observed field dependence of the shielding current. This clearly demonstrates the influence of the coupling properties, i.e., bulk behavior of the oriented grained sample and granularity of the single crystal, on relaxation. Therefore, models exclusively based either on a pinning or on a junction approach alone could not describe our experimental findings. A more appropriate explanation is based on the properties of the defect structure. Depending on field and temperature, defective regions are driven into the normal state whereby additional pinning centers are created which in turn give rise to increasing activation energies. The connectivity of the sample then depends on size and density of these defects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346361
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  • 4
    Electronic Resource
    Electronic Resource
    High current density in bulk YBa2Cu3Ox superconductor (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2352-2354 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A liquid phase processing method for the fabrication of bulk YBa2Cu3Ox superconductors with large current carrying capacity has been developed. Slow cooling through the peritectic transformation (1030–980 °C) has been shown to control the microstructure of these superconductors. A cooling rate of 1 °C/h in this temperature range has yielded a microstructure with long plate type, thick grains oriented over a wide area. Current density up to 18 500 A/cm2 has been obtained by continuous direct current measurements and in excess of 62 000 A/cm2 with pulse current of 10 ms duration and 75 000 A/cm2 using 1 ms pulse. The strong magnetic field dependence observed in sintered bulk 1-2-3 superconductors is also minimized to a large extent where a current density in excess of 37 000 A/cm2 is obtained in a field of 6000 G.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101525
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  • 5
    Electronic Resource
    Electronic Resource
    Anisotropy and intergrain current density in oriented grained bulk YBa2Cu3Ox superconductor (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1575-1577 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intergrain transport current density and its anisotropy have been studied in oriented grained bulk YBa2Cu3Ox superconductors fabricated by the liquid phase processing method. Current density measurements were performed on oriented grained samples with the transport current aligned at different angles to the a-b plane. In these measurements, the transport current passed through several oriented grain boundaries. The results indicate that the critical current density drops rapidly when the transport current flows at small angles to the a-b plane and then decreases slowly at larger angles. At 77 K and zero magnetic field, an anisotropy ratio of about 25 is observed between Jc along a-b plane and that perpendicular to the plane. Further, the critical current density in these samples is found to depend weakly on magnetic field even though the current crosses grain boundaries. These results support the notion that grain boundaries of these superconductors are different in nature from those of solid-state sintered samples.〈squeeze;2p〉
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104129
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  • 6
    Electronic Resource
    Electronic Resource
    Persistent magnetic fields trapped in high Tc superconductor (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1475-1477 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study of field trapping by the incomplete Meissner effect was performed on YBa2Cu3O7−x at 77 K on both sintered and oriented grain samples. Fields of up to BT=1280 G have been trapped in small, oriented grain, planar samples. Circulating persistent current densities of up to 4800 A/cm2 are calculated. Based on these values hollow cylinders of 2 cm i.d. will trap fields of 6000 G. Initial creep is about 10%/week for both types of samples. Creep rate varies as (BT/BT,max)2. BT, due to an external field B0, is BT∝(1−e−cB0/BT,max). Lamination and mosaic assembly steps for producing practical magnets have been performed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103207
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  • 7
    Electronic Resource
    Electronic Resource
    Inductive current measurements in an oriented grained YBa2Cu3Ox superconductor (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1903-1905 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical current of grain aligned YBa2 Cu3Ox bulk material was investigated by inductive flux profile and ac susceptibility measurements. The induced current was directed perpendicular to the a-b plane oriented grains where high values of the transport current, have been previously reported. In spite of the unfavorable geometry of the investigated shielding current, no features of granularity were observed. The results yield a uniform bulk critical current density jc of 3×104 A/cm2 at zero field and 77 K. Field and temperature dependences of this jc are discussed and compared with those in a granular Y-Ba-Cu-O material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102329
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  • 8
    Electronic Resource
    Electronic Resource
    Grain alignment in bulk YBa2Cu3Ox superconductor by a low temperature phase transformation method (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 639-641 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A quench and directional phase transformation process has been developed to achieve grain alignment in bulk YBa2Cu3Ox superconductors at temperatures about 100 °C below the peritectic temperature. Isothermal phase transformation of quenched precursors at 890 °C for 3 min is found to result in the formation of more than 75% of YBa2Cu3Ox phase without any formation of Y2BaCuO5. Phase transformation at higher temperatures leads to rapid formation of Y2BaCuO5 in addition to YBa2Cu3Ox. A well-aligned microstructure is achieved by directional phase transformation of the quenched compacts as a rate of 10 mm/h. The magnetic field dependence of the critical current density at 77 K of the directionally phase transformed material compares well with that of melt-textured YBCO and is superior to that of magnetically aligned and sintered YBCO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112256
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  • 9
    Electronic Resource
    Electronic Resource
    Joining of high current bulk Y-Ba-Cu-O superconductors (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 898-900 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new fabrication method which makes it possible to enlarge the size of small, but high quality, grain-aligned superconductors has been developed. This method involves solid state joining of high current density bulk YBa2Cu3Ox samples prepared by melt-processing. The joined samples exhibit superconductivity above 90 K and are found to be capable of carrying currents in excess of 150 A at 77 K. The interface of the joined samples is found to sustain current densities (Jc) in excess of 6000 A/cm2 at zero field and in excess of 4000 A/cm2 at 1.5 T. Also, the magnetic field dependence of Jc of the joined samples is similar to that of the individual samples. Since this joining method is not limited by the size of the superconductors that can be joined, the favorable transport and magnetic properties render this process suitable for applications requiring high temperature superconductors in bulk forms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106498
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  • 10
    Electronic Resource
    Electronic Resource
    Control of grain alignment to fabricate long Y-Ba-Cu-O superconductors with high current density (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 3313-3315 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A directional solidification method has been developed to grow YBa2Cu3Ox samples in excess of 55 mm in length with uniform grain alignment and a-b planes oriented parallel to the sample length. Using a furnace configuration that yields a negative lateral gradient, the YBa2Cu3Ox grains have been forced to nucleate and grow along the axis instead of at an angle to the sample length. X-ray pole figures analyses along the entire length at different sections show that the a-b planes are aligned parallel to the sample length with deviations less than 5° along the growth direction. Transport critical current density (Jc) measurements over the entire length and at different sections of the sample reveal a uniform current density in excess of 7000 A/cm2 at 1.5 T and 77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106677
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