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  • 1
    Electronic Resource
    Electronic Resource
    Grain orientation in thick laser-deposited Y1Ba2Cu3O7−δ films: Adjustment of c-axis orientation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5545-5548 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Y1Ba2Cu3O7−δ films with a thickness between 0.5 and 5 μm were grown on Si covered with an amorphous SiO2 layer, on Zr foils, and on a single-crystalline MgO substrates by KrF laser ablation. The influence of film thickness and substrate temperature on the structure, texture, and microstructure of the as-grown films was investigated by x-ray diffraction and scanning electron microscopy. At an appropriate, substrate-dependent temperature, on all three substrate materials, the films grow c-axis oriented up to a thickness of about 2 μm (critical thickness), followed by a sharp transition to a-axis-oriented growth occurring within about 100 nm. Similar changes could be observed by lowering the substrate temperature by 120 °C. Therefore, the hypothesis was propounded that the thickness dependence of the growth orientation of the film is due to a decrease of the surface temperature. To prove this the influence of raising the substrate temperature during the growth process was investigated. It could be shown that a linear increase of the substrate temperature leads to completely c-axis-oriented films up to thicknesses of 5 μm. A change of the thermal emissivity of the film surface as a possible cooling mechanism is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359674
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  • 2
    Electronic Resource
    Electronic Resource
    Structure of the Fe-doped high-temperature superconductors Y1Ba2Cu3Oy and Bi2Sr2Ca1Cu2Oy (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1018-1022 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The high-temperature superconductors YBa2(Cu1−xFex)3Oy and Bi2Sr2Ca1(Cu1−xFex)2Oy have been examined by resistivity measurements, x-ray diffraction, and Mössbauer experiments in order to understand the influence of Fe on the structure of the perovskites. The concentration dependence of the Fe substitution and the results of the annealing experiments are consistent with the following model which explains the observed structural changes with Fe composition in YBa2Cu3Oy. For low Fe content, the Fe atoms mainly substitute on the Cu(I) sites leading only to a slight decrease of Tc, but to an attraction of more oxygen ions, which are introduced into the (001) plane. The Fe ions with five- or sixfold coordination act like local symmetry points inducing the formation of short orthogonal chains crossing at the Fe ions. This leads to the orthorhombic-to-tetragonal transition at an Fe concentration of 2.3%. For higher Fe content, Tc more rapidly decreases, probably due to a partial substitution of Fe also on the Cu(II) sites of the perovskite until the superconductivity vanishes near 16% Fe. The three occuring Mössbauer doublets are assigned to different (four-, five-, and sixfold) oxygen environments of the Fe ions. Similar environments occur in Bi2Sr2Ca1Cu2Oy with 20% Fe, although it is known that no Cu-O chains exist in this structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343058
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  • 3
    Electronic Resource
    Electronic Resource
    Oxygen diffusion and phase transformation in Y1Ba2Cu3Ox (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 1642-1645 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed in situ x-ray diffraction experiments, differential scanning calorimetry, and thermogravimetrical analyses are performed during annealing of superconducting Y1Ba2Cu3Ox samples in order to study the influence of the oxygen diffusion on the structure and structural changes of these alloys. The superconducting properties before and after annealing are checked via resistivity measurements. Annealing in vacuum leads to an irreversible and diffusion controlled phase transformation from the superconducting orthorhombic to the semiconducting tetragonal perovskite structure. For small heating rates, the transition starts at about 550 °C. With increasing heating rates the diffusion mechanism causes a delayed onset and a broadening of the temperature regime of the transition. The interdiffusion constant D(700 °C) for oxygen in Y1Ba2Cu3Ox is about 10−12 cm2/s. Annealing at 550 °C in oxygen atmosphere regains the orthorhombic superconducting phase with its properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339897
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  • 4
    Electronic Resource
    Electronic Resource
    Conditions for oriented growth of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O films by pulsed laser ablation (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2405-2409 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O films have been grown in situ on amorphous SiO2 by excimer laser ablation in order to study the growth and orientation of the perovskite structures and to compare it with the epitaxial growth on single-crystalline SrTiO3. Under fixed experimental conditions optimum combinations of the oxygen partial pressure and substrate temperature for the deposition of c-axis oriented films were determined. The results on the morphology and orientation of the grains, which influence the superconducting properties, are discussed with respect to thermodynamic data available for the 123 phase and kinetic constraints. While superconducting transitions Tc of 90 K and critical current densities of about 3×106 A/cm2 at 77 K are obtained on SrTiO3, the values are reduced to about 84 K and 104 A/cm2 on SiO2, respectively, due to the diffusion of Si into the film and the different microstructure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348672
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  • 5
    Electronic Resource
    Electronic Resource
    Growth of the superconducting phase in ceramic Y1.2Ba0.8CuOy samples (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 317-319 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Differently prepared samples with the nominal composition Y1.2Ba0.8CuOy are examined via microscopy, energy dispersive x-ray analysis, x-ray diffraction, and measurements of resistivity and susceptibility. Various phases are identified directly. Essentially these are Y2BaCuO5, which forms a matrix with semiconducting and antiferromagnetic properties and YBa2Cu3O7−x, which is present in a dendritic morphology. The dendritic appearance indicates that YBa2Cu3O7−x is formed by nucleation and growth during sintering. Despite the particular growth mechanism of sintered materials a strong analogy exists with dendritic growth during solid-state transformations in metallic alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99505
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of elastic constants in thin films using hydrogen loading (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 647-649 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By measuring stress and strain that build up in thin films during hydrogen absorption, the elastic constants of the films can be determined, if a one-dimensional elastic behavior occurs only. This will be demonstrated for hydrogen absorption in Nb films. The in-plane stress is determined from the substrate curvature that is measured by using a two-beam laser setup. The out-of-plane strain is measured via x-ray diffraction. Furthermore, this method allows us to distinguish whether the film is plastically or elastically deformed by checking the reversibility of the stress–strain curve. In the case of a 250-nm-thick Nb film, the elastic constants obtained are similar to that of bulk Nb. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123028
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  • 7
    Electronic Resource
    Electronic Resource
    Island growth and surface topography of epitaxial Y-Ba-Cu-O thin films on MgO (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2180-2182 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality epitaxial Y1B2Cu3Ox thin films (Tc,o ≥ (R18) 90 K, jc (77 K)≥ (R18)3 ×106A/cm2) were in situ grown on MgO by KrF excimer laser ablation. The combination of in situ resistance measurements, x-ray diffraction experiments, Tc measurements, scanning electron microscopy and scanning tunneling microscopy gives clear indications for an island growth on these substrates and shows growth steps and spirals at the film surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106066
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  • 8
    Electronic Resource
    Electronic Resource
    Resputtering during the growth of pulsed-laser-deposited metallic films in vacuum and in an ambient gas (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 3766-3768 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To determine the effective sputter yield during pulsed-laser deposition a method by measuring the deposition rate on tilted substrates is proposed. Under vacuum conditions, sputter yields of up to 0.17 and 0.55 were found at a laser fluence of 4.5 J/cm2 for Fe and Ag, respectively. These strong resputtering effects are induced by the large fraction of energetic ions occurring during deposition. With decreasing laser fluence or increasing Ar gas pressure, the sputter yields are reduced due to a decrease of the kinetic energy of the ions. For the deposition of stoichiometric films, an optimum Ar partial pressure of about 0.04 mbar exists, where the deposition rate is highest and the sputter yield is reduced. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125449
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