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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2410-2413 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single-chamber in situ laser processing of high-Tc YBa2Cu3O7−δ film on stainless steel (302) substrates with yttria-stabilized zirconia (YSZ) buffer layers, has been carried out using a multitarget deposition system. YSZ and YBa2Cu3O7−δ films were deposited sequentially by KrF excimer laser (λ=248 nm) at substrate temperature of 650 °C. The films were characterized by x-ray diffraction, four point probe ac electrical resistivity, scanning electron microscopy and Auger electron spectroscopy (AES) techniques. Due to the matching of the thermal expansion coefficient of YSZ with stainless steel and its diffusion barrier characteristics, good quality high-Tc films have been grown on stainless steel substrates with superconducting transition temperature, Tc (onset), of 92 K and Tco (zero resistivity temperature) of 84 K. AES depth profiling indicated little interdiffusion of Fe across the interface of YSZ and stainless steel. A laser evaporation method was used for patterning the YBa2Cu3O7−δ films and critical current density, Jc, was measured to be ∼5×104 Acm−2 at 40 K. It was observed that the zero resistivity temperature significantly changed with the variation of buffer layer thickness, buffer layer processing temperature, and ambient oxygen partial pressure during the deposition of YBa2Cu3O7−δ.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2594-2596 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Good quality superconducting YBa2Cu3O7−δ thin films have been grown on nickel-based superalloy, viz., Hastelloy with yttria-stabilized zirconia buffer layers employing a single chamber in situ pulsed laser deposition process. YBa2Cu3O7−δ films were found to be textured with c axis perpendicular to the substrate. A plot of normalized resistance against temperature exhibited a smooth metallic behavior followed by an onset superconducting transition at 92 K with the zero resistance temperature (Tc0) of 86 K. Critical current density for these films at 77 K was ∼7000 A cm−2 and critical current (Ic) was observed to be proportional to (1 − T/Tc0)1.4.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2351-2353 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ formation of YBa2 Cu3 O7 superconducting thin films by the pulsed laser evaporation technique is critically dependent on the processing conditions (substrate temperature, oxygen partial pressure, subsequent annealing, etc.) and on the deposition setup, including the nozzle geometry required for the incorporation of oxygen. We have studied the recovery of the superconducting properties as a function of location of the oxygen jet relative to a fixed substrate-target setup at a substrate temperature of 550 °C and an oxygen partial pressure of 200 mTorr. Several experiments were performed with the oxygen jet directed on the target and/or on the substrate. During the deposition process, a dc bias voltage of +300 V was applied on an interposing ring, which has resulted in formation of superconducting thin films at a low temperature of 500 °C. Excellent superconducting properties with the Tc zero of 88 K were obtained on films fabricated at 550 °C with the nozzle directed onto the substrate. In contrast, films formed with the oxygen jet directed at the target showed poor superconducting properties, with a Tc0 of approximately 50 K. The x-ray diffraction studies on these films showed much sharper Bragg peaks and higher oxygen content for films fabricated with the oxygen jet directed on the substrate compared to that of the target.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2034-2036 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have prepared highly oriented bismuth cuprate thin films (c-axis textured) on yttria-stabilized zirconia (100) YS-ZrO2 substrates at 650 °C by pulsed excimer laser ablation in a 200 mTorr oxygen ambient. The films were annealed in oxygen and nitrogen atmospheres to study the effect on zero-resistance transition temperature (Tc0). Thin films deposited at 650 °C exhibited a Tc0 of 68 K with onset at 110 K. Post-annealing for 1 h at 400 °C in oxygen improved the Tc0 to 82 K, while the onset remained the same. X-ray diffraction, scanning electron microscopy, and Rutherford backscattering channeling studies were performed on these films for correlations between crystal structure, microstructure, and superconducting properties. X-ray diffraction patterns indicated a 2212 type phase with a=5.39 A(ring) and c=30.76 A(ring); preferential orientation of the c axis perpendicular to the substrate was observed. The lattice parameters and x-ray diffraction patterns were found to be invariant with annealing treatments that improved Tc0 from 68 to 82 K.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1460-1462 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have systematically investigated resistance of a bismuth cuprate Bi1.5Pb0.5Ca2Sr2Cu3Ox as a function of different annealing treatments. X-ray diffraction and transmission electron microscopy studies were performed on concomitant specimens for correlations between structure and superconducting properties. A sharp 110 K superconducting transition was observed in the sample which was isostructural with the n=2 member of the (Bi,Pb)2(Ca,Sr)n+1CunO2n+4+δ family. The zero resistance transition temperature Tc0 was found to be sensitive to annealing at 673 K with a best result of 100 K for 30 min annealing. It is proposed that Tc0 and transition width in bismuth cuprates are sensitive to oxygen stoichiometry.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 993-995 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the use of diamondlike carbon (DLC) films for protecting superconducting YBa2Cu3O7 (YBCO) films against degradation from exposure to moisture and acid. YBCO thin films on single crystal LaAlO3 and MgO substrates were deposited by laser ablation followed by DLC encapsulation. DLC films were deposited at pressures ranging from high vacuum to 0.1 Torr He. Substrate temperature was varied from 20 to 100 °C during the deposition of DLC. The process compatibility of laser ablation was found convenient to sequentially deposit YBCO and DLC films from high purity stoichiometric targets. Epitaxial YBCO films on (100)LaAlO3 (Tc−zero=89 K) and (100)MgO( Tc−zero=85 K) substrates showed identical superconducting transitions before and after encapsulation by a DLC layer. The encapsulated films showed no degradation due to acid treatment or aging over a period of 45 days.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2552-2554 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting YBCO (YBa2Cu3O7) films were deposited on polycrystalline alumina substrates with c-normal orientation. YBCO films deposited directly on alumina exhibited a broad transition with Tc, zero=60 K. The Tc, zero increased to 86 K upon the use of a YSZ (yttria stabilized zirconia) buffer layer to stop the interface reaction. However, the Jc of these films was still below 104 A/cm2. A simple surface modification of the polycrystalline alumina substrate by way of depositing a YSZ buffer and repolishing the surface drastically improved the Jc. Values of 104 A/cm2 observed at 30 K is the best Jc reported so far for YBCO films on polycrystalline alumina. We believe further improvements in both the surface finish of the polyalumina and the YSZ buffer layer will lead to microwave quality YBCO films on polyalumina.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5935-5939 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting properties and microstructures of the YBa2Cu3AgxO7−δ composites have been studied as a function of silver content, 0〈x〈6, using a variety of techniques. The superconducting transition temperature Tc of these composites was found to be the same, ∼90 K, for the above range of composites. For values of x〉3, small quantities of 211 phase were detected along the grain boundaries. Alloy formation between Ag and Cu is proposed to take place which makes the residual composition poor in copper, resulting in the formation of nonsuperconducting 211 phase. The silver is observed in the form of precipitates at very low concentrations of silver, indicating that silver does not substitute for copper in YBa2Cu3O7. Lattice parameters of the composites were found to be invariant throughout the above composition range. The addition of Ag2O in the starting composition seems to stabilize the stoichiometric YBa2Cu3O7 by way of decomposition to Ag and O. As a result, the incorporation of oxygen and recovery of superconducting properties is enhanced in the silver composites.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physica C: Superconductivity and its applications 167 (1990), S. 669-676 
    ISSN: 0921-4534
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physica C: Superconductivity and its applications 156 (1988), S. 827-833 
    ISSN: 0921-4534
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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