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  • Articles  (12)
  • YBa2Cu3O7  (12)
  • Springer  (12)
  • Oxford University Press
  • 1990-1994  (12)
  • 1950-1954
  • Electrical Engineering, Measurement and Control Technology  (12)
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  • Articles  (12)
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  • Springer  (12)
  • Oxford University Press
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  • Electrical Engineering, Measurement and Control Technology  (12)
  • Physics  (12)
  • 1
    Electronic Resource
    Electronic Resource
    Theoretical study of isotope effect in La-doped Y-123 (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 19-25 
    Details
    ISSN: 1572-9605
    Keywords: Isotope effects ; YBa2Cu3O7 ; Cooper pairing interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The recent oxygen isotope effect measurement made in the system YBa2-x La x Cu3O7 (0≤x≤0.5) is analyzed using the “two-carrier” model which describes a superconducting system as a mass anisotropic system consisting of charge carriers with two different masses as a result of lattice defects or oxygen deficiency. The extent to which Ba, Cu, and O atoms participate in the phonon-mediated Cooper pairing interaction is elucidated. The relationship between the theoretically deduced mass anisotropic factor andT c agrees closely with the experimental results of Uemuraet al. [28]. Furthermore, the superconducting energy gap toT c ratio is found to be close to 3.5. Excellent agreement is also achieved between the theoretically calculated oxygen isotopic constant and the experimental results of Bornemann and Morris [12].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618501
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  • 2
    Electronic Resource
    Electronic Resource
    Film thickness dependence of critical current density for YBa2Cu3O7 films post-annealed at a low oxygen partial pressure (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 37-41 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The variation of critical current density at 77 K as a function of film thickness was studied for YBa2Cu3O7 films on (100) LaAlO3 substrates. Film thicknesses were in the range 0.2–1.6μm. The films were deposited by co-evaporation and post-annealed under conditions which have previously resulted in high-quality films (750°C and an oxygen partial pressure of 29 Pa). The critical current density at 77 K exceeds 1 MA cm−2 for the thinner films, and decreases with increasing film thickness in excess of about 0.4μm. The decrease is in rough agreement with a switch fromc-axis toa-axis growth at about this critical thickness. A good anticorrelation was found between room temperature resistivity and critical current density at 77 K. The results are compared to those obtained before by post-annealing at 850°C in 1 atm of oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618503
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  • 3
    Electronic Resource
    Electronic Resource
    Vapor pressures of Y, Ba, Cu precursors for the growth of YBa2Cu3O7 by MOVPE (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 119-125 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; MOVPE ; vapor pressures ; β-diketonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The vapor pressures of theβ-diketonates Y(THD), Ba(THD), and Cu(THD), commonly used as precursors for MOVPE of YBa2Cu3O7, and Y(MCP) were measured at different temperatures. A time-resolved static method recording the pressure vs. time at constant temperature was used, permitting us to deduce the vapor pressure even if the materials tend to decompose. The values of the constants of the Clausius-Clapeyron equation log10p(T)/p 0=A-B/T are,A=11.7, 8.7, 8.27, 16.6 andB=4359, 2654, 3602, and 6453 K for Y(THD), Y(MCP), Ba(THD), and Cu(THD), respectively withp 0= 1 Pa and temperatureT in K. The thermal stability of the sources was measured and are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618055
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  • 4
    Electronic Resource
    Electronic Resource
    Phonon structures in tunneling conductance of superconducting YBa2Cu3O7 (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 367-369 
    Details
    ISSN: 1572-9605
    Keywords: Tunneling conductance ; second derivative ; phonon structure ; YBa2Cu3O7
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We report on measurements of the tunneling conductance structures above the superconducting gap energy using YBa2Cu3O7 polycrystalline junctions. The measured second derivative data are reproducible among the junctions, and the intensities of the common structures at the biases of 37–38, 47–53, 67–77, and 94–95 mV are strong enough to be assigned. These structures are in agreement with those in the neutron phonon density of states in whole energy regions when the energies are measured from the gap edge of 26±1 meV. This correspondence indicates that the electron-phonon interaction contributes to the pairing mechanism of this superconductor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724570
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  • 5
    Electronic Resource
    Electronic Resource
    Raman scattering studies of ultrathin-layer YBa2Cu3O7/PrBa2Cu3O7 superlattices (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 213-216 
    Details
    ISSN: 1572-9605
    Keywords: Raman scattering ; superlattice ; YBa2Cu3O7 ; PrBa2Cu3O7 ; phonon renormalization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We present Raman scattering studies ofc-oriented ultrathin-layer superconducting (YBa2Cu3O7) m /(PrBa2Cu3O7) n superlattices. For the superlattice with (m=2,n=1) sequence, Raman spectra reveal a new line in the spectral region around 320 cm−1. It is interpreted as a mode representing a combination of IR optical phonons of the Y-sublayers with an admixture of aB 1g type Raman active vibration in the Pr sublayers. This new line, which is similar to those from the interior of the Brillouin zone of the original lattice, does not exhibit superconductivity-induced self-energy effects, although its counterpart in the pure substance does. No additional line is found in the (m=1,n=2) superlattice in the same region, supporting our interpretation for the (m=2,n=1) sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730397
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  • 6
    Electronic Resource
    Electronic Resource
    Reproducibility of transition temperature and critical current density of thin films of YBa2Cu3O7 on (100) LaAlO3 (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 61-65 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current ; LaAlO3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Submicrometer epitaxial films of YBa2Cu3O7(YBCO) on (100) LaAlO3 were made by coevaporation and furnace annealing. Samples from more than a dozen runs are used in this study. The zero resistance transition temperature (T c) is high (89 or 90 K) if the film composition is phase pure (Ba/Y=2, Cu/Y=3) or if it is enriched in Ba and Cu. For these compositions the critical current density (J c) at 77 K has an average value of 2×105 A cm−2, with a tendency for decreasingJ c with increasing film thickness (0.2 to 0.8μm). Variations inJ c are not correlated with deviations from ideal stoichiometry. Steeper slopes of the resistance-temperature curves above 100 K and lower values of the room-temperature resistivity are associated with high values ofJ c. If the film composition is enriched in Y relative to Ba and Cu,T c decreases by several degrees.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618299
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  • 7
    Electronic Resource
    Electronic Resource
    Critical current density and microstructure of YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 143-147 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current density ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Post-annealing of thin films of YBa2Cu3O7 (YBCO) has been performed at 29 Pa and 750°C. For films 0.6 μm thick, a critical current density 〉1 MA cm−2 is obtained at 77 K, with a sharp eddy current response at 25 MHz. Microstructural investigation of these films by crosssectional and planar transmission electron microscopy reveals that the YBCO film has thec-axis normal to the plane of the substrate in a continuous sheet of varying thickness, frequently covering the entire thickness of the film. Mutually perpendicular rods with thec-axis in the plane of the LaAlO3 substrate are also seen. The microstructure and critical current density of these films are compared with those of previously reported films post-annealed in atmosphericpressure oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618058
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  • 8
    Electronic Resource
    Electronic Resource
    Process monitoring during post-annealing of YBa2Cu3O7 thin films containing fluorine (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 167-170 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; post-annealing ; process monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The post-annealing method of producing thin films of YBa2Cu3O7 (YBCO) has taken on a new impetus due to the recent work showing that films of the highest quality can be made by using low partial pressures of oxygen during the annealing cycle. Here it is shown that for films produced by using BaF2 as a source material, the post-annealing procedure can be closely controlled by monitoring the F that evolves due to the water vapor reaction with BaF2. The use of an ion-sensitive electrode allowed small F evolution rates (about 1 ng s−1) to be detected above background, sufficient to measure the F evolution rate from even the smallest samples used. The time interval during which F evolves was found to increase with increasing YBCO film area being annealed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618062
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  • 9
    Electronic Resource
    Electronic Resource
    High-quality YBa2Cu3O7 films on 4-in. Wafers of sapphire, gallium arsenide, and silicon (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 231-233 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; thin films ; large-area deposition ; semiconductor substrates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Our technique of reactive thermal co-evaporation has been extended to fabricate large films (up to 4 in.) of YBa2Cu3O7 with high quality. A rotating substrate holder is used to separate the deposition and oxidation processes. This allows free access of the metal vapors. As large substrate wafers we use Al2O3, Si, and GaAs with buffer layers of CeO2, YSZ, and MgO, respectively. On all substrates, the uniformity of thickness and composition was better than 2%. Inductively measuredT c andj c (77 K) were 87.5±0.2 K and 〉1×106 A/cm2, respectively, across the full wafer area. This holds also for GaAs substrates due to a new procedure of capping by Si3N4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730401
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  • 10
    Electronic Resource
    Electronic Resource
    Temperature dependence of the infrared optical properties of YBa2Cu3O7: A plasmon damping model (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 481-483 
    Details
    ISSN: 1572-9605
    Keywords: High-T c superconductors ; YBa2Cu3O7 ; infrared ; plasmon ; resistivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The temperature dependence observed in the mid- and near-infrared optical properties of YBa2Cu3O7 is explained in terms of the Drude model for free charge carriers. In the Drude model, the linear temperature dependence of the dc resistivity arises from the free charge carriers having a temperature-dependent mean free path. This temperature dependence results in the plasmon contribution to the dielectric constant having a damping coefficient which also varies linearly with temperature. We find that the temperature dependence which is observed in the absorption and reflection spectra of YBa2Cu3O7 is consistent with this simple model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724594
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  • 11
    Electronic Resource
    Electronic Resource
    Microwave properties of highly oriented YBa2Cu3O7-δ superconducting thin films (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 253-257 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; microwave properties ; R s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have performed millimeter-wave frequency (94 GHz) measurements on high-quality YBa2Cu3O7-δ superconducting films on yttrium-stabilized (100) ZrO2 and MgO substrates. The ∼0.2μm thin films fabricated by magnetron sputteringin situ with the YBa2Cu3O7-δ powders as target exhibit superconducting transition temperatures up to 88 K. The critical current density of 6×105 A/cm2 at 77 K and the X-ray diffraction spectrum as well as scanning electron microscope photographs indicate these thin films are fullyc-axis oriented, extremely high in density, and universally homogeneous. Millimeter-wave surface resistances have been measured on a hemisphere open resonator in the temperature range of 20 K toT c and beyond. The surface resistance at 94 GHz and 77 K for these films is found to be about 30 mΩ, nearly 1/4 that for copper, and a drop of two orders in the surface resistance within 4 K is observed, which indicates that these films are good materials for applications in the millimeter-wave range, especially for fabricating microwave devices. We observed such low surface resistance in these thin films due to the near absence of grain and phase boundaries coupled with a high degree of crystalline orientation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618145
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  • 12
    Electronic Resource
    Electronic Resource
    Optimization of annealing temperature for YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 279-282 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; annealing temperature ; LaAlO3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Post-annealing of YBa2Cu3O7 (YBCO) thin films is usually performed at 850–900°C in atmospheric-pressure oxygen. In this study, coevaporated YBCO films on LaAlO3 were post-annealed in an oxygen partial pressure of 29 Pa at temperatures in the range 700–825°C. Zero resistance transition temperatures were 89–90 K. Both d.c. (room-temperature resistance and critical-current density) and a.c. parameters (extracted from eddy-current response measurements at 25 MHz) were monitored. The optimum temperature is close to 750°C, which is on the YBCO thermodynamic stability line at this low oxygen partial pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618149
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