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  • 2000-2004  (12)
  • 1990-1994  (12)
  • 1
    Digitale Medien
    Digitale Medien
    The role of high-pressure sintering in preparing high-quality n-type Nd2−xCexCuO4−y superconductors (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 843-849 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: High-pressure high-temperature sintering (HHS) under 1.0, 2.0, 4.0, and 6.0 GPa for a short time was directly used to reduce n-type Nd1.85Ce0.15CuO4−y. Superconductors with higher critical temperature were obtained. The samples display lower resistivity, and more metalliclike resistance behavior at normal state with increasing sintering pressure. A small increase of lattice parameter and cell volume was observed via electron and x-ray diffraction. Transmission electron microscopy studies also show that there is a preferential orientation along the c axis among the neighboring grains. This helps get well-matching grain boundaries in the HHS samples. A Cu2O high-pressure phase was found via energy-dispersive x-ray analysis in the sample treated above 5.0 GPa, which is thought to be a deleterious factor for superconductivity. Sintering under suitable pressure not only enhances the intragranular conductivity, but also effectively improves the intergranular links. Finally, via the assumed interstitial oxygen ordering in the T' structure, a possible mechanism of n-type reduction is proposed based on the change in tolerance factor under reduction atmosphere and high pressure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.353323
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  • 2
    Digitale Medien
    Digitale Medien
    Comparison of transport scattering and single-particle relaxation times in modulation-doped heterostructures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 390-394 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The transport scattering and single-particle relaxation times which characterize a two-dimensional electron system have been investigated by using thermal neutron irradiation. The ratios of transport scattering time to single-particle relaxation time are observed to vary from 1.7 to 7.8 depending on the electron density. A decrease in single-particle relaxation time is found while the transport scattering time increases as the electron concentrations increase. These phenomena are relevant to the Hall plateau broadening and enhancement of Shubnikov–de Haas oscillations in such an experiment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.357086
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  • 3
    Digitale Medien
    Digitale Medien
    New family of high Tc superconductors in the (Tl1−xMx)Sr2(Ca1−yYy)Cu2O7−δ system (M=IVA and VA elements) (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 2492-2494 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A new family of high Tc superconductors with superconducting transition temperatures ranging from 40 to 100 K have been synthesized in the (Tl1−xMx)Sr2 (Ca1−yYy)Cu2O7−δ (M=Ti, Zr, Hf, V, Nb, and Ta) system. Here, we use as an example, vanadium and yttrium substitution into the thallium and calcium sites, respectively, in the parent compound TlSr2CaCu2O7 to demonstrate the substitutional chemistry, crystal structure, and superconductivity for these new superconductors.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.104180
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  • 4
    Digitale Medien
    Digitale Medien
    Granular growth of Fe3O4 thin films and its antiphase boundaries prepared by pulsed laser deposition (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7398-7400 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Fe3O4 thin film prepared by pulsed laser deposition on Si (100) substrate has been investigated by transmission electron microscopy from plane and cross-sectional views. The thin film, which shows a spinel structure as characterized by selected-area diffraction, is about 180 nm thick with granular growth of particle size about 50 nm. High resolution electron microscopy observations indicate reduced thickness of the native SiO2 layer between the thin film and Si due to rastering of the substrate surface by an unfocused laser beam before the deposition. By using a 220 diffraction spot in two beam condition near the 〈001〉 axis of a single Fe3O4 grain, antiphase boundaries (APBs) inside the grains could be clearly resolved. The existence of APBs in the thin film is consistent with the magnetic experiments including an open hysteresis loop and unsaturated magnetization in relatively high magnetic fields. This study suggests that APBs are not unique to Fe3O4 films grown on MgO substrates. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1358831
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  • 5
    Digitale Medien
    Digitale Medien
    Magnetic properties of iron and iron platinum alloys synthesized via microemulsion techniques (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5615-5617 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this article, metallic iron, and iron/platinum alloys nanoparticles have been synthesized via chemical assembly and magnetically characterized. Fabrication of iron and iron/platinum particles was achieved by reducing 0.1 M aqueous metal salts confined in the polar portions of inverse micelles of cetyltrimethylammonium bromide with borohydride. The dc susceptibility of a sample of 8 nm iron nanoparticles exhibits a blocking temperature of 54 K and coercivity of 200 G at 10 K. The presence of the gold coatings prevented oxidation and allowed the samples to be manipulated without additional precautions to prevent oxidation. Two iron/platinum alloys have been synthesized and verified by x-ray powder diffraction and transmission electron microscopy. Magnetic characterization is performed using superconducting quantum interference device magnetometry. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372468
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  • 6
    Digitale Medien
    Digitale Medien
    Improvements of microstructural and superconducting properties of Ag-Bi2Sr2CaCu2Ox screen-printed tape by controlled oxygen partial pressure during cooling procedure (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 833-835 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effect of different cooling procedures, after sintering, on the microstructural and superconducting properties of Bi2Sr2CaCu2Ox (B-2212) screen-printed tapes has been investigated. It was found that the amorphous phase originally present in grain boundaries at the sintering temperature undergoes a conversion to the Bi-2212 phase during slow cooling. However, the excess oxygen absorbed during slow cooling (in 21% oxygen) disturbs the order and ordering process of Bi-2212 crystals, but if the slow cooling process is conducted under monotonically reduced oxygen partial pressure, to ensure that the optimum oxidation state at sintering temperature of the Bi-2212 phase can be retained during the cooling procedure, tapes are then characterized by narrow grain boundaries and the highest Jc value (approximately-greater-than)104 A/cm2 at 77 K and 0 T.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.109897
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  • 7
    Digitale Medien
    Digitale Medien
    Superconductivity and microstructure of n-type Ln1.85Ce0.15CuO4−y (Ln=Pr, Sm, Eu) produced under high-pressure sintering (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3037-3039 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using an unconventional reduction method, high-pressure sintering at 6.0 GPa and about 600 °C for 20 min, we have produced high-quality n-type Ln1.85Ce0.15CuO4−y (Ln=Pr, Sm, and Eu) superconductors from the as-prepared materials. The samples show higher critical temperatures, higher superconducting phase fractions, and much lower resistances in the normal state than those synthesized by conventional methods. The increase of critical temperature in Eu1.85Ce0.15CuO4−y is most obvious with an onset temperature Tonc and zero-resistance temperature Tc0 of 28.4 and 23.3 K, respectively. High-pressure sintering seems to be effective on the modulation of the fine crystal and electronic structures of n-type systems. In particular, metallic resistance versus temperature behaviors in normal states similar to those found in single crystals and epitaxial films are observed in Sm1.85Ce0.15CuO4−y and Eu1.85Ce0.15CuO4−y, in sharp contrast to the semiconductorlike behaviors in the conventionally prepared samples. From transmission electron microscopy studies, it is found that the compacting and regrowth of the polycrystal under high-pressure sintering greatly improves the weak links at grain boundaries.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.109131
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  • 8
    Digitale Medien
    Digitale Medien
    Self-organized type-II In0.55Al0.45As/Al0.50Ga0.50As quantum dots realized on GaAs(311)A (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3741-3743 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Self-organized In0.55Al0.45As/Al0.50Ga0.50As quantum dots are grown by the Stranski–Krastanow growth mode using molecular beam epitaxy on the GaAs(311)A substrate. The optical properties of type-II InAlAs/AlGaAs quantum dots have been demonstrated by the excitation power and temperature dependence of photoluminescence spectra. A simple model accounting for the size-dependent band gap of quantum dots is given to qualitatively understand the formation of type-II In0.55Al0.45As/Al0.50Ga0.50As quantum dots driven by the quantum-confinement-induced Γ→X transition. The results provide new insights into the band structure of InAlAs/AlGaAs quantum dots. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.126768
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  • 9
    Digitale Medien
    Digitale Medien
    Magneto-shape-memory effect in Co–Ni single crystals (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3660-3662 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A Co–33 wt % Ni single crystal was grown by an optical floating-zone furnace without crucible in a high-purity argon atmosphere. In the [001] direction, the as-grown single crystal exhibited a saturation magnetization of 124 A m2/kg, which is nearly twice as high as that of Ni2MnGa, a typical magneto-shape-memory material. A reversible strain of 3% was induced by an applied pulse magnetic field of 2 T in the [001] direction in the temperature range between Md and Ms. According to the martensitic transformation theory [T. Y. Hsu (Z. Y. Xu), Sci. China, Ser. E: Technol. Sci. 40, 561 (1997)] for fcc (γ)→hcp (cursive-epsilon), a possible mechanism based on the reversible motion of the Shockley partial dislocations is proposed in this letter. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1376148
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  • 10
    Digitale Medien
    Digitale Medien
    Effects of temperature oscillations on the growth of carbon nanotubes by chemical vapor deposition (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 828-830 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have grown carbon nanotubes at oscillatory growth temperature by chemical vapor deposition. The high-resolution transmission electron microscopy (HRTEM) images show that they contain a number of incomplete carbon layers both on the outer and inner periphery and dislocations in the middle part of the carbon nanotubes walls. The defect structure of these nanotubes depends on the period of the T oscillation. In addition, HRTEM examinations of these carbon nanotubes from end-on reveal that some have polyhedral sections and contain dislocations. These features make them more active chemically and might have significant influence on the properties and applications of the carbon nanotubes. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.125598
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