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  • 11
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 3284-3286 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comparative study of the superconducting properties of pristine and stage 1 iodine intercalated Bi2Sr2CaCu2O8+δ single crystals is presented. We find the anisotropy of the penetration depth to be significantly reduced after intercalation. Specifically, the penetration depth perpendicular to the CuO2 planes is dramatically decreased, by about 60%. Reducing the anisotropy improves the position of the irreversibility line in the low field region where pinning is weak. However, in high fields the position of the irreversibility line is depressed. This can be explained by the influence of strong flux pinning. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 81-83 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of the YBa2Cu4O8 phase has been studied with respect to oxygen partial pressure P(O2 ) and temperature by x-ray diffraction, thermogravimetry, and differential thermal analysis. The critical temperature Td for the decomposition of YBa2Cu4O8 phase was determined from thermal analyses. It was found that Td was strongly dependent on P(O2 ) and the following empirical relation was obtained: log[P(O2)(atm)]=12.41−(1.449×104)/Td(K). It was found that, when heated, YBa2Cu4O8 first decomposed into YBa2 Cu3.5 O7.5−z plus CuO for 0.02 atm〈P(O2 )〈9 atm, while for P(O2 )≤0.02 atm, it decomposed into YBa2Cu3O7−z plus CuO without yielding YBa2Cu3.5O7.5−z .
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2105-2107 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We prepared nearly single-phase polycrystalline samples of HgBa2Ca2Cu3O8+δ(Hg-1223) without and with Pb doping, i.e., Pb-free Hg-1223 and (Hg0.8Pb0.2)-1223, by means of a sample encapsulation technique. According to quantitative energy dispersive x-ray spectroscopy analyses and iodometric oxygen titration, the Pb-free Hg-1223 and the (Hg0.8Pb0.2)-1223 sample were identified to be Hg0.97Ba2.00Ca2.04Cu3.00O8.33 and (Hg0.79Pb0.29)Ba2.00Ca1.98Cu2.94O8.42, respectively. The highest Meissner-signal onset temperatures for the Pb-free Hg-1223 (after post-annealing in O2 gas) and the (Hg,Pb)-1223 (as-sintered) sample were observed at 135.4 and 132.0 K, respectively. The difference in the irreversibility fields (Hirr) for both samples was very small at temperatures above 80 K, while, at temperatures below 70 K, the Hirr versus T curve for the (Hg,Pb)-1223 sample shifted toward the higher field side. Thus, Pb doping was effective for the improvement of magnetic property of Hg-1223 superconductors, at least, at temperatures below 70 K. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 14
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract TiN films were deposited on (100)-Si substrates by RF-reactive sputtering. The effects of processing parameters and substrate orientation on the stoichiometry, resistivity and microstructure of reactively sputtered TiN thin films were investigated. The RF-power was fixed at 50 W, and the nitrogen content in the working gas was adjusted so that target nitridation occurred at a relatively low nitrogen content, 2.6% N2, in a fixed total flow rate of gases of 46.25 standard cubic centimetres (sccm). The N2 percentage was varied from 2.6% to 15.4%. The films were continuous and ∼200 nm thick. Films deposited with the substrate facing the target exhibited 111-texturing, while films on substrates lying in the same plane of the target surface had 100-texturing. Both X-rays photoelectron spectroscopy and high-resolution detailed scans of the Auger electron energy spectrum were used for the stoichiometry determination. On the 100-textured TiN films, the N/Ti ratio was ∼1.0 at low N2 flow rates; the N/Ti ratio rapidly increased with N2 flow rate, and then levelled off. The films had resistivities ranging from 85 to 1340 µΩ cm, and the functional dependence of both N/Ti and the resistivity values behaved similarly with increasing N2. X-ray single-line profile analysis of the 200-reflection indicated that the average crystallite size decreased and the average strain increased with increasing nitrogen content in the working gas. The Si/TiN structures were heat treated in the temperature range from 300 to 600°C in a quartz tube under 1 atm (∼105Pa) of flowing high purity Ar gas. Heat treatment at 300°C did not affect the TiN film integrity, while treatment at 400–600°C resulted in void-type defects.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Neuroradiology 36 (1994), S. 625-626 
    ISSN: 1432-1920
    Keywords: MRI-Spinal cord-Brain stem ; Demyelination ; Multiple sclerosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Postmortem magnetic resonance imaging (MRI) of the spinal cord and the brainstem in a patient with multiple sclerosis are compared with the histopathological findings. Abnormal high signal intensity areas on T2-weighted images correspond precisely to demyelinated areas.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 7 (1994), S. 55-58 
    ISSN: 1572-9605
    Keywords: Sr-Ca-Cu-O superconductor ; high-pressure synthesis ; oxidizer ; “0223” structure ; “infinite-layer” structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract It is shown for (Sr, Ca)1−y CuO2.00+z (nominal composition) superconductors fabricated under a high pressure of 5 GPa and at 930°C that, as z increases, the Meissner fraction increases from a few percent to 20% and then starts to decrease. In the X-ray powder diffraction pattern for the sample with the maximum Meissner fraction, it is obvious that the “infinite-layer” structure has been decomposed and a new structure becomes the major phase. It appears that the new structure is the “0223” structure which consists of rock-salt and the “infinite-layer” type blocks. This material is likely to be a new superconducting cuprate.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 28 (1993), S. 4104-4112 
    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 Radio-frequency-sputtered barium titanium silicate (BST, Ba2Si2TiO8) thin films were grown on crystalline Si (100) substrates and were characterized using wavelength-dispersive spectrometry (WDS), X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM), and diagonal techniques for dielectric properties. The chemical compositions of the films increasingly deviated from stoichiometry with film thickness. At the initial stage of deposition the grain configuration is dependent on the Si substrate texture. XRD analysis indicates that the BST films deposited at an optimum substrate temperature of 845 °C were strongly c-axis oriented, and that the film orientation is manipulated by substrate temperature and supersaturation. The corresponding film-growth rate in the direction normal to the film surface at 845 °C was 1.95 nm min−1 at the initial stage, and decreased with sputtering time. The as-deposited films have a room-temperature bulk resistivity of 1.8 ×107 Ωm in the direction of thickness and an isotropic surface resistivity of 1.5×103 Ωm. The high-frequency relative dielectric constant, 0.05 at frequencies higher than 9 MHz, is lower than that of many typical piezoelectric materials. The high-frequency impedance character is typical of piezoelectric materials, giving a minimum impedance frequency of 9.0 MHz and a serial resonant frequency at about 9.5 MHz.
    Type of Medium: Electronic Resource
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  • 18
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The rare-earth site of samples having the compositions (Fe,Cu)Sr2(Eu,Ce) n Cu2O4+2n+z (n=2 and 3) were studied by151Eu Mössbauer spectroscopy. The results obtained are compared with measurements of EuBa2Cu3O7−δ (1∶2∶3) and Bi2Sr2(Ca1−yEuy)Cu2O8+E (2∶2∶1∶2) samples. The full quadrupole Hamiltonian of the 21.5-keV γ-transition was applied in analyzing the measured spectra. Simultaneous fitting of spectra recorded from crystallites oriented in various directions was used to determine the hyperfine parameters of then= 2 and 3 samples. Two different electric field gradients, not discernible in simple random crystallite measurements, were obtained for then=3 series.
    Type of Medium: Electronic Resource
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