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  • 1
    Electronic Resource
    Electronic Resource
    Microwave surface resistance of YBa2Cu3O7 thin films on LaAlO3 substrates (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2514-2516 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface resistance Rs of YBa2Cu3O7 (YBCO) thin films (0.6±0.1 μm) deposited onto 2.5-cm diam (100) LaAlO3 substrates has been measured at 22 GHz using both Cu and Nb cavities. The surface resistance falls precipitously at the superconducting transition (Tc =90 K) from a normal state value of approximately 2 Ω to a 77 K value of 13.7±1 mΩ, which is 1.6 times lower than Cu. At 4 K the surface resistance is 1±0.1 mΩ, as measured in a Nb superconducting cavity, which is an order of magnitude lower than Cu. The critical current density at 77 K is 4.5×104 A/cm2. Pole figure analyses show the ratio of c-axis to a-axis-oriented material in the film is 2.4:1. YBCO films deposited onto either LaGaO3 or LaAlO3 substrates with varying c/a ratios yield surface resistance values at 77 K that are crudely correlated with Rs. Therefore, the principal effect of orienting the material is to improve the sharpness of the high-frequency superconducting transition, consistent with the notion that the sharpness is associated with intergranular rather than intragranular properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346493
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of in-plane epitaxy on magnetotransport properties of (La0.5Sr0.5)CoO3 thin films (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 695-697 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have systematically studied the temperature- and magnetic field-dependent resistance in (La0.5Sr0.5)CoO3 (LSCO) films with various degrees of in-plane texturing using the biaxially oriented LSCO on CeO2/YSZ/SiO2/Si substrates. We find that the ferromagnetic transition temperature, Tc, is much the same in all samples while the resistive transition exhibits metallic behavior (dR/dT〉0) in the epitaxial LSCO to semiconducting behavior (dR/dT〈0) in the poorly textured LSCO. The magnetoresistance (MR) in the epitaxial LSCO on a LaAlO3 substrate displays two distinct regions; the low field hysteretic MR related to the magnetization hysteresis and the high field linear negative MR due to the suppression of spin fluctuations. In contrast, the MR in the biaxially textured LSCO sample shows only the hysteretic behaviors at low fields and no linear MR at high fields. Compared to the polycrystalline-doped LaMnO3 which shows an enhanced MR at low fields, the MR in the biaxially oriented LSCO does not exhibit such characteristics. We attribute this to the differences in the spin polarization between LSCO and the doped LaMnO3. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121951
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  • 3
    Electronic Resource
    Electronic Resource
    Relationship between film thickness and the critical current of YBa2Cu3O7−δ-coated conductors (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3692-3694 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: During the development of YBa2Cu3O7−δ (YBCO) coatings on flexible metal tapes, it has become evident that the achievable critical current (Ic) reaches a maximum value of about 200 A per cm of conductor width at a coating thickness of 1–2 μm. Additional YBCO beyond this thickness can actually reduce Ic. To investigate, critical current density (Jc) has been measured for samples with YBCO ranging from 0.39 to 6.3 μm in thickness. Several films were thinned by ion milling and remeasured with two significant results: almost no supercurrent is carried at thickness levels above 2 μm; and for films thicker than 3 μm, Jc is drastically reduced near the substrate as well. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125431
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  • 4
    Electronic Resource
    Electronic Resource
    High-temperature superconducting thick films with enhanced supercurrent carrying capability (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 1601-1603 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a multilayer architecture to enhance the supercurrent carrying capability of thick (〉1 μm) YBa2Cu3O7−x (YBCO) films. An interlayer of CeO2, which functions as a starting template for growth of subsequent high-quality YBCO layers, is used to prohibit the generation of microstructural defects that otherwise develop in the top region of thick YBCO films. Improved surface quality for a 3.3 μm thick YBCO film has been confirmed by the channeling data of Rutherford backscattering spectroscopy and by scanning electron microscopy. Compared to our routinely prepared single-layer YBCO thick film in which the supercurrent drops rapidly with increasing film thickness, this multilayer makes it possible to maintain critical current density over 1 MA/cm2 with less restrictions on the thickness of coated conductors. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1455143
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  • 5
    Electronic Resource
    Electronic Resource
    Microwave surface resistance of YBa2Cu3Cu3O7−x films on polycrystalline ceramic substrates with textured buffer layers (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1626-1628 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used a parallel-plate resonator technique to measure the microwave surface resist- ance Rs of YBa2Cu3O7−x (YBCO) films on buffered ceramic substrates at around 10 GHz, and studied the correlation between their Rs and materials properties. A 0.4-μm-thick YBCO film (with an in-plane mosaic spread of 7°) grown on a polycrystalline alumina substrate with an ion-beam-assisted-deposited yttria-stabilized zirconia buffer layer showed an Rs of 1.89 mΩ at 76 K and 0.21 mΩ at 4 K. We have observed a strong correlation between the Rs of the samples and the in-plane mosaic spread of the YBCO films. This correlation can be explained qualitatively in terms of a simple model in which the weak links between the grains of the YBCO film form an electrical network of Josephson junctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117052
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  • 6
    Electronic Resource
    Electronic Resource
    Microwave power absorption by thallium-based superconductors on metallic substrates (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1329-1331 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tl-based superconducting thick films deposited on large-area (11.4 cm2) Ag alloy (Consil 995) substrates have been characterized by surface resistance measurements yielding values of 4 and 14 mΩ at 4 and 77 K, respectively, as measured in an 18 GHz Cu cavity; corresponding Cu values are 8 and 21 mΩ. Utilizing a Nb cavity, the dependence of surface resistance on microwave power was also measured. The surface resistance begins to rise in microwave magnetic fields of 1–10 Oe and saturates in 20–60 Oe, the exact values depending on the degree of c-axis texturing of the polycrystalline films. Enhanced texturing sharpens the high-frequency transition into the superconducting state and also weakens the dependence of surface resistance on microwave magnetic field. These results are significant for high temperature superconductor applications such as microwave cavities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104300
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  • 7
    Electronic Resource
    Electronic Resource
    Power-dependent microwave properties of superconducting YBa2Cu3O7−x films on buffered polycrystalline substrates (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 3293-3295 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the microwave properties of 0.4 μm thick YBa2Cu3O7−x (YBCO) films on polycrystalline substrates with ion-beam-assisted-deposited yttria-stabilized zirconia buffer layers using a parallel-plate resonator technique at 10 GHz. The YBCO films with similar in-plane texture grown on both forsterite and Ni-based alloy substrates show similar microwave properties. We measure low-power surface resistance Rs values of about 0.5 mΩ at 76 K and 0.15 mΩ at 4 K for films with an in-plane mosaic spread of about 7°. Single-tone power-dependence measurements show that the surface resistance and the surface reactance increase linearly and by the same amount with increasing microwave field level. At intermediate power levels, the intermodulation measurements show odd-order intermodulation products that increase quadratically with two-tone input power. These results indicate a hysteretic vortex penetration mechanism in the weak links as the most plausible source of the observed nonlinearities in these films. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118431
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Properties of YBa2Cu3O7−δ thick films on flexible buffered metallic substrates (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2397-2399 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report superconducting and mechanical properties of YBa2Cu3O7−δ (YBCO) thick films on Ni-based alloys with a textured yttria-stabilized zirconia (YSZ) buffer layer. The YBCO and YSZ layers were deposited by pulsed laser deposition and ion beam assisted deposition, respectively. It was found that the transport critical current density (Jc) correlates very well with the YBCO mosaic spread. Jc over 1×10 6 A/cm2 at 75 K and ∼1×107 A/cm2 at 4 K were obtained in the 1-μm thick YBCO films. Zero field critical current of 120 amps at 75 K was obtained in a 2-μm-thick and 1-cm-wide YBCO film. Angular dependence measurement revealed Jc peaks for both H(parallel)c and H(parallel)a-b. The peak for H(parallel)c implies additional pinning due to defects such as small angle grain boundaries or twin boundaries. Bending tests at 75 K showed that the YBCO thick films on the metallic substrates could sustain a strain of 0.4% and over 1% for tension and compression, respectively. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114559
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  • 10
    Electronic Resource
    Electronic Resource
    Microwave surface resistance of magnetron-sputtered Tl-Ba-Ca-Cu-O films on silver substrates (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2147-2149 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Surface resistance measurements on Tl-Ba-Ca-Cu-O thick films (∼15 μm) magnetron sputtered onto BaF2-buffered, silver-based (Consil 995) substrates have been made at a microwave frequency of 22 GHz. The relatively large-area films (∼5 cm2) are characterized by surface resistance values of 6.9±2 mΩ at 11.3 K and 30.2±1 mΩ at 77 K; the corresponding values for Cu are 10 and 22 mΩ, respectively. These results demonstrate that Tl-Ba-Ca-Cu-O can be deposited onto large-area, metallic substrates with characteristic surface resistance values lower than Cu at 4 K. Orientation of the film should improve the surface resistance at 77 K, thereby making the fabrication of microwave cavities that are superior to Cu possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102954
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