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  • 1
    Electronic Resource
    Electronic Resource
    Electrodynamic Properties of High Temperature Superconductor Films (1993)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 130-132 (Jan. 1993), p. 373-404 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/00/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.130-132.373.pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Low-resistivity epitaxial YBa2Cu3O7 thin films with improved microstructure and reduced microwave losses (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5572-5578 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial thin films of YBa2Cu3O7 have been prepared on SrTiO3 and LaAlO3 substrates by a high-pressure planar dc-sputtering technique. By covering the substrate heater with a frame of polycrystalline YBa2Cu3O7 substantial improvements of the YBa2Cu3O7 film properties were achieved. These are characterized by dc-resistivity values ρ(T) of less than 50 μΩ cm at 100 K and ρ(300 K)/ρ(100 K) values of up to 3.9. Significant deviations from the usual linear ρ(T) behavior were found. Critical temperatures above 90 K, resistive transition widths down to 0.3 K, and critical current densities of about 5 × 106 A/cm2 at 77 K confirm the high quality of the films. As indicated by Rutherford backscattering and high-resolution transmission electron microscopy the films exhibit a microstructure characterized by a reduced density of lattice defects. However, lattice-coherent precipitates with a diameter of about 5–10 nm were observed. As an outstanding feature the films exhibit, besides the initial steep falloff at Tc, a further gradual decrease of the microwave surface resistance at 87 GHz below 50 K by at least one order of magnitude. These results are very promising for millimeter-wave applications of epitaxial YBa2Cu3O7 thin films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350535
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  • 3
    Electronic Resource
    Electronic Resource
    The effective microwave surface impedance of high Tc thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 6940-6945 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dependence of the effective surface impedance Zeff=Reff+iXeff of superconducting thin films on the film thickness d, on the magnetic field penetration depth λ, and on the dielectric properties of the substrate material is investigated theoretically by means of impedance transformations. It was found that the effective surface resistance Reff can be expressed by RSf(d/λ)+Rtrans where RS is the intrinsic surface resistance of the superconductor. The function f(d/λ) describes the altered current density distribution in the film. Rtrans arises from power transmission through the film. It depends on d and λ as well as on the dielectric properties of the substrate material and is significantly altered in the case of a resonant background. The effective surface reactance Xeff of a superconducting thin film can be expressed by XS cosh(d/λ) where XS=ωμ0λ is the intrinsic surface reactance. Measurements of Zeff at 87 GHz have been performed for YBa2Cu3O7−δ thin films grown epitaxially by laser ablation on SrTiO3, MgO, and LaAlO3. With the best films, Reff (77 K) values of 21 mΩ and RS (77 K) values of 8 mΩ were achieved. The temperature dependence of λ was found to be in good agreement to both weak-coupling BCS theory in the clean limit and the empirical two-fluid model relation with λ (0 K) values ranging from 140 to 170 nm and 205 to 250 nm, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345037
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  • 4
    Electronic Resource
    Electronic Resource
    High quality epitaxy of YBa2Cu3O7−x on silicon-on-sapphire with the multiple buffer layer YSZ/CeO2 (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1429-1431 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High quality YBa2Cu3O7−x films on silicon-on-sapphire were grown using a multiple buffer layer, consisting of YSZ and CeO2. Ion channeling reveals the high crystalline perfection of the YBa2Cu3O7−x films. A channeling minimum yield for the Ba signal as low as 3% was measured. The normal state resistivity of 200 μΩ cm at 300 K, critical temperatures above 90 K, with transition widths down to 0.5 K, critical current densities above 2×106 A/cm2 at 77 K and surface resistance values of 1.4 mΩ at 18.9 GHz and 77 K confirm the high quality of the YBa2Cu3O7−x films. These results are very promising for integrated superconductor and semiconductor applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109647
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  • 5
    Electronic Resource
    Electronic Resource
    Power and magnetic field-induced microwave absorption in Tl-based high Tc superconducting films (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 307-309 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The increase in the microwave surface resistance Rs of high Tc superconductors at elevated microwave power levels is reported for both oriented and unoriented Tl-based films as a function of rf magnetic field at 820 MHz and 18 GHz. The application of dc magnetic fields produces qualitatively similar increases in Rs and in the surface reactance Xs. The increase in Rs with dc field is shown to arise from simple decoupling of grains by intergranular magnetic flux. The increase in Rs with microwave power, on the other hand, is a consequence of hysteretic intergranular processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104670
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  • 6
    Electronic Resource
    Electronic Resource
    Neutron-induced microwave loss in ceramic YBa2Cu3O7−δ (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2462-2464 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An increase by over three orders of magnitude from 0.58 mΩ to 1.17 Ω was observed at 4.0 K in the 3 GHz microwave surface resistance of ceramic YBa2Cu3O7−δ following exposure to neutrons. The transport resistivity of an unirradiated pellet was linear in temperature down to Tc with a room-temperature value of 2.13 mΩ cm and a resistivity extrapolated to 4.0 K of 0.53 mΩ cm. Following irradiation, the resistivity rose with decreasing temperature from a room-temperature value of 1.5 Ω cm to a maximum at around 45 K with little change evident at Tc . These results, in conjunction with eddy current, susceptibility, iodometric titration, and thermally stimulated luminescence measurements on irradiated and unirradiated samples, collectively suggest that the effect of neutron irradiation has been to decrease intergranular coupling without the development of an insulating phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103256
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  • 7
    Electronic Resource
    Electronic Resource
    Filament-wound composite soft tissue prostheses:controlling compliance and strength by water absorption and degradation (1993)
    Springer
    Journal of materials science 4 (1993), S. 285-291 
    Details
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: This paper deals with the effect of water absorption on the mechanical performance of selectively biodegradable filament-wound composite soft tissue prostheses. It shows how the water absorption phenomenon can be utilized as a new concept of material design, in contrast to the current view that associates moisture absorption by composite materials exclusively with damage. Harnessing water absorption to property design of vascular grafts has two advantages. The first is the controlled increase of the compliance of the graft during healing, aiming to reach a final stage of isocompliance with the host artery. The second is the water-induced biodegradation which enables regulation of the mural porosity during healing of an initially impervious graft. Filament-wound composite vascular prostheses comprising partially biodegradable matrices, different compositions and various winding angles are studied. Water absorption and material degradation are expressed in terms of relative weight gain/loss, which in turn is correlated with changes in the compliance and in the ultimate strength of the grafts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122282
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  • 8
    Electronic Resource
    Electronic Resource
    Survey of microwave surface impedance data of high-T c superconductors—Evidence for nonpairing charge carriers (1990)
    Springer
    Journal of superconductivity 3 (1990), S. 235-242 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7−δ ; microwave ; surface resistance ; penetration depth ; two-fluid model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The microwave surface impedance of the high-T c oxide superconductors has been measured at many laboratories around the world. A survey of their data between 100 MHz and 150 GHz for polycrystalline as well as single crystalline samples is given, focusing on YBa2Cu3O7−δ . In comparison to the classical superconductors, these results reveal a very similar temperature dependence of the surface impedance close toT c but an anomalous high residual surface resistance at lower temperatures. Both features can be explained by the assumption that oxide superconductors contain a significant number of nonpairing charge carriers. Within the framework of a properly extended two-fluid model, this is shown by analysis of our best thin-film data. Moreover, the enhanced losses in polycrystalline material especially for superposed magnetostatic fields result, to a large extent, from the deeper penetration depth. The possible origin of the nonpairing charge carriers and their impact on the applicability of the oxide superconductors is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00625263
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  • 9
    Electronic Resource
    Electronic Resource
    Microwave surface impedance of YBa2Cu3O7−x :S-wave versusD-wave pairing (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 459-461 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; surface impedance ; pairing state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The low temperature behavior of the microwave surface resistanceR s and the penetration provides information on the pairing state. Fully oxygenated films with low de-resistivity in the normal state exhibit an exponential temperature dependence corresponding to values of the energy gap up to 10 meV. For oxygen deficient films a linearR s(T) was observed, similar to single crystals. This can be explained qualitatively by induced superconductivity in the copper-oxygen chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724589
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  • 10
    Electronic Resource
    Electronic Resource
    Microwave surface resistance of epitaxial YBa2Cu3O7 thin films at 18.7 GHz measured by a dielectric resonator technique (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 195-201 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; microwave cavities ; sample surface impedance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We used a dielectric resonator technique for highly sensitive measurements of the temperature dependence of the microwave surface resistanceR s of 1×1 cm2 superconducting films at 18.7 GHz. It consists of a sapphire disc positioned on the film under investigation within a copper cavity which is acting as a radiation shield. In the TE01δ oscillation mode the highly reproducible quality factor of about 105 results in a sensitivity of ±50μΩ forR s measurements. The temperature dependence ofR s can be measured up to values as high as 1 Ω. We have investigated several YBa2Cu3O7 thin films prepared by high oxygen pressure d.c. sputtering on LaAlO3 and NdGaO3. Our best films exhibit a pronounced nonlinear behavior of the d.c. resistivityρ(T) withρ(300K)/ρ(100K) values of about 3.7. Those films show, besides the initial fall-off just belowT c , a further strong decrease ofR s at low temperatures. This was observed both at 18.7 GHz and 87 GHz, as measured by a conventional cavity end plate replacement technique. ForT≪Tc/2 these films exhibit an exp (−αT c/T) dependence ofR s withα-values around 0.4. These observations may be explained by a superconducting energy gap with 2Δ/kT c≈0.8 for charge carriers localized in the CuO chains for YBa2Cu3O7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618067
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