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  • 1
    Electronic Resource
    Electronic Resource
    Doping mechanism in Bi(Pb)-Sr-Ca-Cu-O superconductors (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4878-4885 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model that explains the doping mechanism in Bi(Pb)-Sr-Ca-Cu-O superconductor is presented. X-ray microanalysis reveals that the excess oxygen can be accounted for by the exact stoichiometry of the n=2 and 3 phases. We show that the presence of excess oxygen associated with the structural modulation in the compound is not sufficient to explain the hole concentration required by the transition temperature observed. Using a bond valence argument, we show that the effective valence of the Bi ion in the BiO bilayers is smaller than the expected value of +3, due to the incomplete oxygen coordination around the Bi ion. The model qualitatively explains the observations of lowering of Tc with Er (or Tm) doping or oxygen annealing. The role of Pb addition is suggested to be one of altering the thermodynamics and kinetics of formation of the n=3 phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343806
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  • 2
    Electronic Resource
    Electronic Resource
    Substrate effects on the properties of Y-Ba-Cu-O superconducting films prepared by laser deposition (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 4591-4598 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting thin films of Y1Ba2Cu3Ox with superconducting transition temperature (Tc) near 90 K have been prepared by a laser deposition technique. We show that films prepared on sapphire, lithium niobate, and strontium titanate under identical processing conditions exhibit different electrical characteristics. The film surfaces, interfaces, and crystallinity have been studied by a number of analytical techniques. We conclude that the substrate influences the film properties primarily in three ways: the thermal expansion mismatch introduces cracks in the film, the interface reaction changes the film composition, and the substrate lattice influences the crystallographic orientation of the film.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340136
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  • 3
    Electronic Resource
    Electronic Resource
    Grain boundaries and defects in superconducting Bi-Sr-Ca-Cu-O ceramics (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 379-387 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defects and structural interfaces in superconducting Bi-Sr-Ca-Cu-O have been characterized by transmission electron microscopy. The superconducting phase exhibits frequent variations in the stacking sequence (polytypoids). Dislocations, observed inside the grains, either introduce or accommodate the shear in the a-b plane and the local composition fluctuations. In general, the grains exhibit a platelike morphology with the a-b plane as the grain boundary plane. Grain boundaries along the short edge are generally disordered, whereas those near the long edge generally have a thin layer of the lower Tc polytypoid. Coherent intragranular boundaries are also observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345266
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  • 4
    Electronic Resource
    Electronic Resource
    Thick films of Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O by solution processes (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6382-6387 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have prepared superconducting thick films of the Bi-based and the Tl-based cuprates via the decomposition of aqueous-glycerol solutions containing the salts of the elements. Preliminary results are presented in this work. The substrates are coated prior to heat treating, either by dipping or by spraying on various substrates heated at 200 °C. Short firing times are required in order to minimize the loss of the constituent Bi (Tl). We find that nitrates of the constituents dissolved in a water-glycerol solution increase the reaction rate in comparison to pure nitrate aqueous solutions. They also help to produce the correct superconducting phase before some reaction with the substrate occurs or too much of the constituent Bi (Tl) is lost during heating to form the superconducting phase. However, the thallium phases cannot be obtained if the films are not fired in the presence of a high pressure of thallium in a sealed capsule. The films are composed of platelets, a few microns large, that are on average oriented parallel to the substrate with their c axis normal. The Bi films show an onset temperature at 85 K and zero resistance at 75 K while the Tl films show an onset temperature of 105 K and zero resistance at 95 K. The critical currents obtained to date are quite low (∼50 A/cm2 at 77 K for the thallium phase).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342075
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  • 5
    Electronic Resource
    Electronic Resource
    Bulk and thick films of the superconducting phase YBa2Cu3O7−y made by controlled precipitation and sol-gel processes (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 2725-2729 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The synthesis of high-temperature superconducting oxides using solution chemistry has been investigated and physical properties are compared to ceramics obtained by conventional solid-state reactions. We report on controlled precipitation and sol-gel processes, both of which produce materials with particle sizes smaller than 5 μm. We find that the superconducting properties of the high Tc ceramics are affected by their manner of preparation, such that the transitions are slightly lower in temperature, but sharper, for samples made by solution rather than solid-state chemistry. The ability to prepare stable viscous gels provides an opportunity for obtaining large areas of superconducting coatings. For thick films on alumina or silicon substrates, contamination from the substrate is shown to be a problem. Finally, we observe that the sol-gel process lowers the synthesis temperature by 100 °C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340967
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  • 6
    Electronic Resource
    Electronic Resource
    Superconducting AgMo6S8 thin films prepared by reactive sputtering (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 4829-4834 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Preferentially oriented thin films of the Chevrel-phase superconductor AgMo6S8 were prepared by reactive sputtering. Ag and Mo were simultaneously sputtered from separate guns onto sapphire substrates held at about 850 °C with H2S gas injected near the substrate. The films have superconducting critical temperatures up to 9.2 K and narrow-phase transitions. The reactive sputtering process chosen for the preparation of our films makes it possible to change the superconducting properties and the microstructure of the samples in a systematic way by changing individual preparation parameters and to study which of the preparation conditions are the most crucial for the formation of the Chevrel phase. We find that the superconducting transition temperature of the Chevrel phase is very sensitive to both substrate temperature and to the flow of H2S but insensitive to the background pressure in the chamber before deposition. The microstructure can be changed by controlling the H2S pressure. X-ray measurements show that the films are preferentially oriented with the rhombohedral 001 planes parallel to the surface of the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338347
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  • 7
    Electronic Resource
    Electronic Resource
    Two-dimensional modulated ferrimagnetic systems (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4903-4903 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bi2Sr2MnOy, isomorphic to the high-Tc compound containing Cu, exhibits a displacement modulation driven by the bending of Bi double layers, thus creating a modulated environment for the magnetic MnO2 layers which are 12 A(ring) apart. Neutron scattering results will be presented, showing antiferromagnetic order in zero field and a field-induced transition to weak ferromagnetism. This behavior is a direct consequence of the structural modulation which breaks the symmetry of two otherwise equivalent ordering directions of (010) and (100)−the latter being associated with weak ferromagnetism. Magnetic scattering has been observed at superlattice positions, suggesting that the displacement modulation affects the valence of the magnetic ions. Subtle differences in magnetic behavior are observed in similar compounds where Pb is substituted for Bi and Ca for Sr. These results will be discussed in terms of a modulated magnetic model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348950
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  • 8
    Electronic Resource
    Electronic Resource
    Lithium molybdenum nitride (LiMoN2): the first metallic layered nitride (1992)
    s.l. : American Chemical Society
    Chemistry of materials 4 (1992), S. 928-937 
    Details
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cm00022a033
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  • 9
    Electronic Resource
    Electronic Resource
    Structural and electronic instabilities in M2+Mo6S8 compounds (1985)
    s.l. : American Chemical Society
    Inorganic chemistry 24 (1985), S. 2598-2604 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00211a005
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  • 10
    Electronic Resource
    Electronic Resource
    Rheological study of a gel-forming precursor for superconducting YBa2Cu3O7−x (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 700-702 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rheological measurements are used to monitor the sol-gel behavior of a superconducting precursor. A precursor made with an aged yttrium component [Y(OH)3] has a much higher elastic modulus (G') and complex viscosity (η*) but the same loss modulus (G‘) compared to that made with a fresher yttrium solution. The G‘/G' ratio is less than unity for the older solution but greater than 1 for the fresher sample, indicating that the former solution has a more gel-like character. The high viscosity sample gives better fired thick-film superconducting properties but has a shorter shelf life. Measurements on yttrium components of different age show differences in viscosity and G‘/G' which correlate with the behavior of the oxide precursors. Reshearing the precursor solution at any stage during its gelation process can cause irreversible changes in the gel structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.100645
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