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  • 1
    Digitale Medien
    Digitale Medien
    Activity and diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 and Tl1Ba2Ca2Cu3 alloys (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5635-5641 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have measured the activity and diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 and Tl1Ba2Ca2Cu3 at 930 and 900 °C, respectively, by a modified coulometric titration method on the galvanic cell: O(underbar) in liquid alloys/yttria stabilized zirconia/air, Pt. The standard Gibbs formation energy and the diffusivity of oxygen in liquid Ag-Yb1Ba2Cu3 alloy for 1/2O2(1 atm)→O(underbar)(1 at. %) are determined to be ΔG=−247.4 kJ/g atom, and D=1.52×10−4 cm2/s. The oxygen solubility Cs in the Ag-Yb1Ba2Cu3 alloy is 0.0913 at. %, a factor of 5.5 higher than that in Yb1Ba2Cu3 alloy. The addition of Ag does not alter the growth mechanism and the oxygen diffusion controls the film growth. The growth speed is enhanced as a result of the enhanced oxygen solubility. ΔG and the diffusion coefficient of oxygen in the Tl1Ba2Ca2Cu3 liquid alloy are −257 kJ/g atom and 1.2×10−4 cm2/s, respectively. The oxygen solubility of the Tl1Ba2Ca2Cu3 alloy at 900 °C is found to be very high at ∼5.74 at. %. All thermodynamic data for oxygen in the precursor alloys are consistent with each other but there is a deviation of activity coefficient with composition for the different alloys from the theoretical model.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351963
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  • 2
    Digitale Medien
    Digitale Medien
    Magnetic properties of epitaxial single crystal ultrathin Fe3Si films on GaAs (001) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6766-6768 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Magnetic properties of Fe3Si films with thickness from 2 to 210 monolayers (ML) epitaxially grown on GaAs (001) were studied using a superconducting quantum interference device and alternating gradient force magnetometers. Growth of these single-crystal intermetallic compound films were carried out in a multichamber molecular beam epitaxy (MBE) system. The samples were covered in situ with Au 50 A(ring) thick to prevent oxidation when the samples were removed from the MBE chamber. All the films are ferromagnetic even for samples as thin as 2 ML. The easy magnetization direction of the films is parallel to the film surface. The magnetic coercivity forces (Hc) of the samples increase as the film thickness decreases to 10 ML, and then decrease when the film thickness decreases further to 2 ML.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.352479
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  • 3
    Digitale Medien
    Digitale Medien
    Concentration-dependent oxygen diffusion in Tl1Ba2Ca2Cu3 and Ag1Tl2Ba2Ca2Cu3 superconductor precursor alloys (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3511-3513 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: To study the growth mechanism in growing superconducting thin films by the liquid-gas-solidification process, oxygen diffusivities in liquid Tl1Ba2Ca2Cu3 and Ag1Tl1Ba2Ca2Cu3 precursor alloys were measured by a modified coulometric titration method. The diffusivities of oxygen are very high of the order of 10−4 to 10−3 cm2/s. The logarithm of oxygen diffusivities is found to be reciprocally proportional to the logarithm of oxygen concentrations. This concentration-dependent oxygen diffusivity phenomenon has not been observed in many metallic liquids investigated previously. An interstitial diffusion mechanism may contribute to the fast oxygen diffusion. The strong bonds between Ba and O atoms are proposed to enhance the configurational structural order and hence to quicken the oxygen diffusion that varies the oxygen concentration in Tl1Ba2Ca2Cu3 and Ag1Tl1Ba2Ca2Cu3 superconductor precursor liquids. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359985
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  • 4
    Digitale Medien
    Digitale Medien
    Processing of a TlBa2Ca2Cu3Oy superconducting film by liquid-gas solidification (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2836-2838 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We succeed for the first time in growing a superconducting TlBa2Ca2Cu3Oy film on MgO〈100〉 substrate using a liquid-gas solidification process (LGS). The films are grown in situ; they are deposited by LGS. There is no post-anneal or compensation of Tl applied after the initial deposition. The as-grown film shows a flat and uniform morphology with the c axis perpendicular to the MgO〈100〉. It exhibits a resistant transition onset of 117 K and zero resistance at 103 K.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.104751
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  • 5
    Digitale Medien
    Digitale Medien
    Simple Nb metal bonding structure (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2191-2193 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A simple metallic bonding structure, has been developed consisting of a pure metal Nb and an alloy containing Sn, which can be employed to bond a semiconducting laser device and/or a silicon integrated circuit die to a submount with Au–Sn solder. Differential scanning calorimetry, transmission electron microscopy, and scanning electron microscopy reveal that the Nb layer acts effectively both as an adhesion layer to SiO2 and diamond submounts and as a perfect diffusion barrier against Au–Sn solder. The metallization structure shows no indication of dewetting of the Au–Sn solder. The excellent bonding characters have been attributed to the unique metallurgical properties of Nb. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.113943
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  • 6
    Digitale Medien
    Digitale Medien
    Significantly improved mechanical properties in Pb-free, Sn-Zn-In solder alloy by Ag doping (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1100-1102 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The 87%Sn-8%Zn-5%In alloy is a new Pb-free solder designed for possible drop-in replacement of Pb-Sn solders. This Sn-Zn-In solder has a melting point of ∼188 °C, which is comparable to that of the widely used eutectic Pb-Sn solder. However, because of the rather coarse and nonuniform distribution of platelike, dendritic features throughout the microstructure, the alloy exhibits a limited ductility (tensile elongation of ∼20%). In this letter, we show that the addition of small amounts of Ag (as small as 0.1%) dramatically improves the tensile ductility to ∼40%. The observed improvement in ductility is attributed to the elimination of the coarse planar features and nonuniformities within the microstructure. The addition of Cu has a similar beneficial effect, although it is less preferable to the Ag addition from the stand point of melting temperature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.112110
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  • 7
    Digitale Medien
    Digitale Medien
    Spontaneous patterning in high temperature superconducting film by liquid-gas-solidification processing (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1045-1047 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Without any post physical or chemical patterning a Tl-base high temperature superconducting film has been observed to pattern spontaneously on SrTiO3 (100) by liquid-gas-solidification process. The film exhibits the morphology of a microelectric network in which the directions of growth of the crystal walls follow the directions of the SrTiO3 (100) substrate. The crystal walls consisting of Tl-1223 and Tl-1212 phases are 0.25–1 μm wide, 2 μm high, and a few millimeters long. These walls are proposed to grow from independent nucleation sites and coalescence to form semiconductive junctions. The network exhibits a superconducting transition onset at 113 K and approaches zero resistance at 95 K. Below 95 K, the resistance increases exponentially with decreasing temperature. This strongly suggests that the films form a natural superconductor/semiconductor/superconductor junction array.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.112147
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  • 8
    Digitale Medien
    Digitale Medien
    Activity and diffusivity of oxygen in a liquid Yb1Ba2Cu3 high temperature superconducting precursor alloy (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 760-762 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The activity and diffusivity of oxygen in a liquid Yb1Ba2Cu3 high temperature superconducting precursor alloy have been measured by modified coulometric titration method in a temperature range from 913 to 957 °C. The standard Gibbs formation energies and the diffusivity of oxygen in liquid Yb1Ba2Cu3 for 1/2O2 (1 atm)→O (1 at. %) are determined to be ΔG=−655.20+0.335T(K) (±1.5) kJ/mol and D=1.8×10−2 exp(−48 100/RT) (cm2/s) where R=8.314 J/deg×mol. Despite very strong bonding of oxygen to the liquid alloys, the diffusion coefficient of oxygen is relatively high in the order of 10−4 cm2/s. The solubility of oxygen in the liquid alloy is low, of about 0.0145 and 0.017 at. % at 913 and 935 °C, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.106561
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  • 9
    Digitale Medien
    Digitale Medien
    Reactivity of C60 in pure oxygen (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2956-2958 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In pure oxygen at moderate temperatures of 200 °C, an fcc C60 transforms into amorphous carbon-oxygen compounds and the icosahedral C60 molecular structure is destroyed. The maximum oxygen uptake of pure C60, O/C60, is 12. Isothermal TGA transformation curves are sigmoid-shaped with the kinetic exponent n∼5/2 which conforms with a two-dimensional nucleation and growth mode. The heat of formation for the carbon-oxygen compounds is 90 kcal/mol O, and the formation energy for the reaction: 60C (graphite)→C60 molecule is estimated to be ∼600 kcal/mol.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.105810
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  • 10
    Digitale Medien
    Digitale Medien
    New Pb-free solder alloy with superior mechanical properties (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 15-17 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: New high-strength Pb-free solder alloys, based on the Sn-Ag-Zn system, have been developed. A relatively small addition of Zn significantly improves the mechanical strength of Sn-3.5% Ag eutectic solders while maintaining the same level of ductility. The observed increase in strength is as much as 48% over that of the Zn-free alloy. This strengthening from the Zn additions is attributed to a substantial refinement of the precipitates in the solidification microstructure. The problems of nonuniformity in solidification dendrite structure and solder surface roughness often observed in the Sn-Ag binary alloys are also alleviated by the Zn addition. It is found that essentially all of the added Zn resides in the more corrosion-resistant, Ag-based, intermetallic precipitates, leaving the Sn-rich matrix primarily free of Zn in solid solution. High-temperature creep tests indicate that the new Zn-containing alloys exhibit a remarkably improved creep resistance of more than an order of magnitude.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.109734
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