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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 457-459 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An electron diffraction and microscopy study is presented of a variety of phases in the Y:Ba:Cu:O system in which superconductivity occurs. The superconducting phase is demonstrated by convergent beam electron diffraction to be centrosymmetric with space group Pmmm, in contrast to a previous determination of Pmm2. This discrepancy arises from local symmetry-breaking defects. In addition to this phase and a cubic BaCuO2 phase, we characterize two other phases. One is the Y-rich orthorhombic phase: Pnma with a=13.5 A(ring), b=6.3 A(ring), and c=7.6 A(ring). The second occurs by a phase transition of the superconducting Pmmm phase to P4/mmm with a=3.85 A(ring), c=11.7 A(ring). The superconducting phase may now be described as either an ordered array of oxygen vacancies in the perovskite structure, or an ordered array of oxygen interstitials in the new tetragonal phase, which may explain how the material can lose oxygen reversibly.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2856-2858 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High critical-current densities, Jc, have been observed in single crystals and thin films of YBa2Cu3Ox. Jc in bulk materials is diappointingly low reaching a maximum in untextured material of about 103 A cm−2. The importance of raising Jc in bulk materials is paramount and most applications of bulk materials require high Jc in high magnetic fields. The work of Jin et al. in raising Jc to 17 000 A cm−2 in zero field represents a most important step in the development of bulk materials and gives real hope to bulk applications. In the communication we first describe the properties of untextured wire, and then we describe our process for melt texturing and the difficulties encountered.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] YBa2Cu3Ox was prepared by calcining BaCO3 (99.9%), Y2O3 (99.9%) and CuO (99.9%) at 900 °C for 10 h followed by commi-nution in a polymer vibro energy mill using ZrO2 media. The resultant powder had a surface area of 3 m2 g"1 yielding an equivalent spherical diameter of 0.3 |xm. This powder was ...
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 347 (1990), S. 455-457 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] By far the most successful method to date for producing high-toughness composites is the infiltration of a ceramic fibre preform with a gaseous ceramic precursor5. Several months are required to produce parts only a few millimetres thick, however, and several steps of surface grinding are ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 339 (1989), S. 130-132 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The size of defects in a ceramic can be estimated from the Griffith theory of fracture6"8. The bending strength cr of a ceramic rod has been related to the flaw size/, measured microscopically on a polished surface, by the equation a = 0.737 KJf 1/2 (1) where Klc is the fracture ...
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 23 (1988), S. 761-768 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The physical and mechanical properties of YBa2Cu3O7−° superconductors are examined. These properties are related to powder preparation method, powder characteristics, sintering behaviour and sintered microstructure. The sintering atmosphere and sintering schedules affect the final microstructure very strongly and determine, in conjunction with starting powder characteristics, the sintered density. The mechanical properties such as Young's modulus, bend strength and critical stress intensity factor (fracture toughness) are measured and related to microstructure as determined by electron microscopy. Control of microstructure by careful powder selection and sintering schedule is seen as key to optimizing the physical and mechanical properties of the material. Finally attention is drawn to fabrication techniques and how these must be optimized in order to realize the mechanical properties which are necessary if these are to be useful as engineering materials. Comparisons between fabrication techniques show that uniaxial powder pressing suffers from limitations in terms of specimen complexity and densification whereas the favoured route, termed viscous processing, gives a more homogeneous microstructure, higher strength and allows near theoretical density to be achieved.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 10 (1991), S. 671-674 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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