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  • 1
    Digitale Medien
    Digitale Medien
    Influence of experimental conditions on the electric field effect in the ceramic (BiPb)2Sr2Ca2Cu3Ox (1997)
    Springer
    Physics of the solid state 39 (1997), S. 1759-1761 
    Details
    ISSN: 1063-7834
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract An experimental study is reported of the influence of temperature (T), electric field polarity (±E), as well as of changes in the electrode/insulator/superconductor (E/I/S) measuring system on the field effect in the ceramic (BiPb)2Sr2Ca2Cu3Ox. It has been established that at 77 K and for E⩾60 MV/m the critical current I c and conductivity of the sample increase for I〉I c, irrespective of the field polarity. For lower fields and a negative electrode potential the conductivity in an electric field may decrease. The field effect decreases with increasing temperature, to practically vanish near T c where the sample is still in superconducting state. Experiments carried out with more complex systems E/I/M/I/S and E/I/M/S (M stands for a metallic foil) support the conclusion that it is the external electric field that is responsible for the observed effects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.1130166
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  • 2
    Digitale Medien
    Digitale Medien
    I–V characteristics and the electric-field effect in melt-grown YBa2Cu3Ox/Y2BaCuO5 HTSC crystals (2000)
    Springer
    Physics of the solid state 42 (2000), S. 1207-1210 
    Details
    ISSN: 1063-7834
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The effect of an electric field E=120 MV/m in the electrode-insulator-superconductor system on I–V curves obtained at 77 K on two types of single-crystal samples cut from monolithic superconducting YBa2Cu3Ox/Y2BaCuO5 has been studied. The Y211 nonsuperconducting phase in the ingot was in the form of precipitates ≈1 µm in size. It has been found that an electric field applied to samples with a comparatively low Y211 content (volume fraction 8%) does not affect the critical current I c while reducing the resistance R at currents slightly above I c . In samples containing more than 35% Y211 phase, electric field results in an increase of I c and a decrease of R for I〉I c . Data on the critical temperature T c and the temperature dependence of I c have also been obtained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.1131363
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  • 3
    Digitale Medien
    Digitale Medien
    Some physical properties of an Al2O3-SiC-TiC composite (1997)
    Springer
    Technical physics letters 23 (1997), S. 923-926 
    Details
    ISSN: 1090-6533
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Ceramic samples obtained by hot pressing from a mixture of Al2O3 with admixtures of 23 vol.% TiC powder and 30.9 vol.% SiC whisker crystals are investigated experimentally. The resistivity of the material is measured at temperatures of 4.2–300 K, the infrared reflection spectra are recorded in the region 400–4200 cm–1, and the temperature dependence of the Young’s modulus is investigated at temperatures up to 1300 K. As a result it is it is shown that the conductivity and optical reflection of the high-strength composite have a semimetallic character, which is due to the titanium carbide particles contained in it.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.1261934
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  • 4
    Digitale Medien
    Digitale Medien
    Properties and chemical stability of hot-rolled Ag(7 at. % Cu)-sheathed Bi2Sr2Ca0.64Cu1.64Ox powder-in-tube tapes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4596-4607 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Bi2Sr2Ca0.64Cu1.64Ox (nominally Bi2212) powders were fabricated into powder-in-tube Ag- and Ag(7 at. % Cu)-sheathed tapes by cold and hot rolling to investigate the effects of sheath composition and rolling conditions on their microstructural development and superconducting properties. Bi2212 tapes with Ag(Cu) sheaths exhibited improved grain alignment and interfacial uniformity, as well as enhanced formation of the Bi-free phase (≈Sr7.5Ca6.5Cu14Ox), relative to the Ag-sheathed specimens. The hot-rolled Ag(Cu)-sheathed tapes displayed superior critical current densities (Jc), where magnetization Jcm=1.5×106 (H(parallel)c) and 4.6×105 A/cm2 (H⊥c) at T=5 K, H=1 T. Correspondingly, these specimens had transport critical current densities (Jct) of 6.7×104 A/cm2 (H(parallel)c) and 5.4×104 A/cm2 (H⊥c) at T=4.2 K, H=0 T and 2.2×104 A/cm2 (H(parallel)c) and 3.0×104 A/cm2 (H⊥c) at T=4.2 K, H=14 T. The chemical stability of the Ag(Cu) sheath regions during the partial melting process was also studied. Rapid oxidation of copper produced Cu2O precipitates in the sheath at 885 °C, and subsequently a Cu2O-free zone developed near the core/sheath interface. A theoretical analysis of Cu2O precipitate formation and decomposition during thermal processing is presented. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359805
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  • 5
    Digitale Medien
    Digitale Medien
    Transport critical current density and microstructure in extruded YBa2Cu3O7−x wires processed by zone melting (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 228-232 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: YBa2Cu3O7−x compounds were extruded into long wires with the diameter of 1 mm after sintering. The sintered wires were subsequently zone melted to develop a highly textured microstructure. Magnetization experiments at 77 K indicated a Jc value of 1×105 A/cm2 at 1 T. Transport measurements at 77 K showed a greatly enhanced field dependence of the critical current density. Transmission electron microscopy revealed an important grain-boundary feature which eliminated the weak-link behavior. Large amounts of dislocations have also been found in the zone-melted sample which may contribute to flux pinning in the system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.347122
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  • 6
    Digitale Medien
    Digitale Medien
    Single-crystal YBa2Cu3O7−x and Bi2Ca1+xSr2−xCu2O8+y surfaces and Ag adatom-induced modification (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3130-3135 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Comparison of x-ray photoemission results for single crystal and polycrystalline YBa2Cu3O7−x allows us to identify oxygen vacancies in the Cu-O chains and determine their effects on the Cu, Ba, and Y core level line shapes. The deposition of adatoms of Ag onto single crystals of YBa2Cu3O7−x and Bi2Ca1+xSr2−xCu2O8+y leads to changes in the Cu 2p3/2 emission indicative of slight Cu2+ to Cu1+ surface reduction, with greater modification for the 1-2-3's than the 2-1-2-2's. O 1s core level results show Ag-induced broadening because of these surface effects. The Ba 3d and Y 3d structures showed minimal changes for the 1-2-3 surface. Ag deposition onto the 2-1-2-2 samples also leads to Bi dissociation and subsequent surface segregation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.342709
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  • 7
    Digitale Medien
    Digitale Medien
    Surface reactivity and interface morphology for Ti growth on YBa2Cu3O7−x, Y2BaCuO5, and CuO (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 1995-2002 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: X-ray photoemission results make it possible to compare Ti adatom reactivity with clean surfaces of CuO, Y2BaCuO5, and YBa2Cu3O7−x. Changes in the Ti 2p1/2,3/2 and O 1s core level emission during overlayer growth are related to surface reactions between the Ti adatoms and oxygen atoms leached from the substrates. The results show the growth of a TiO2-like reaction species at initial Ti depositions, the formation of Ti suboxides at intermediate coverages, and the onset of metallic behavior at higher Ti coverages. The Ti-O reaction products grow in a layer-by-layer fashion initially, but Ti metal overlayer growth occurs as clusters on this Ti-O reacted region. Substrate modifications associated with Ti-O reactions result in significant changes in the chemical environments of Cu, Ba, and Y for Y2BaCuO5 and YBa2Cu3O7−x.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.345580
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  • 8
    Digitale Medien
    Digitale Medien
    High-temperature deformation of YBa2Cu3O7−δ (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2079-2082 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Steady-state flow stress of dense (99% of theoretical) polycrystalline YBa2Cu3O7−δ has been measured in direct compression at temperatures between 870 and 980 °C in oxygen partial pressures of 0.03, 0.18, and 1.0×105 Pa for strain rates between 5×10−6 and 4×10−5 s−1. The stress exponent was close to one, indicating that diffusional flow was the dominant deformation mechanism. The flow stress decreased with decreasing oxygen partial pressure, obeying a power law with an exponent of approximately 1/2 . The activation energy was about 800 kJ/mol at an oxygen partial pressure 1×105 Pa, but decreased to 600 kJ/mol at a pressure of 3×103 Pa.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.344300
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  • 9
    Digitale Medien
    Digitale Medien
    Influence of oxygen concentration on processing YBa2Cu3O7−x (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2485-2488 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The sintering kinetics of YBa2Cu3O7−x have been studied from 870 to 930 °C in oxygen/argon mixtures ranging from 0.2% to 100% oxygen. For sintering at temperatures below that required for formation of any liquid phase, densification rates increased with decreasing oxygen concentration, and transport critical current densities increased with increasing density. The activation energy for sintering was 190±30 kJ/mol.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.344260
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  • 10
    Digitale Medien
    Digitale Medien
    A time-temperature-transformation diagram for the orthorhombic to tetragonal phase transition in YBa2Cu3O7−∂ (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 5411-5414 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An isothermal transformation curve marking the orthorhombic (O) to tetragonal (T) phase transition boundary has been established over a wide temperature range. There exists within the time-temperature-transformation diagram two distinct and separate regions containing superconducting samples with narrow 90- and 60-K transition temperatures, respectively. An oxygen diffusion coefficient at 300 °C in these materials is estimated based on isothermal data. The kinetic process of the T-O transformation is studied. It is found, at all temperatures investigated, that extended annealing reduces the normal-state conductivity of the material and that the best samples are produced for intermediate annealing times.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.340360
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