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  • 1990-1994  (8)
  • 1985-1989  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Transmission electron microscopy study of V-Sr-Tl-O system (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 1057-1059 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the structure of V-Sr-Tl-O system with transmission electron microscopy. The majority phase in VSrTl0.2Oy samples with a sharp resistivity drop around 165 K is identified as V2Sr0.6TlδOy with δ ranging from 0.01 to 0.04. This phase has a hexagonal structure, with point group 6/mmm, space group P6/mmm, and lattice parameters a=0.569 nm and c=1.284 nm. Upon in situ cooling from room temperature to 130 K, no evidence of structure change is observed. When the crystals of V2Sr0.6TlδOy are heated in situ, two superstructures are formed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349695
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetization relaxation in YBa2Cu3O7−δ (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1671-1675 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time and field sweep rate dependencies of magnetization in high temperature superconductors are derived from a combined view based on the thermally activated flux creep. The τ0 in the magnetization relaxation expression M=M0+M1 ln(1+t/τ0) is a macroscopic quantity related primarily to the sample geometry and other experimental conditions via the effective activation energy U(J0). This activation energy provides an alternative interpretation to the nearly inverse proportionality of τ0 to the field sweep rate. The values of τ0 in the magnetization relaxation of single crystal YBa2Cu3O7−δ are consistent with the calculated ones. As the nonlinear U(J) is taken into account, the curvature in the ||M||-ln t plot may change from negative to positive over a sufficiently long time window, and the magnetization hysteresis M(H) depends on the field sweep rate H(overdot) by const+A ln H(overdot)+B ln2 H(overdot), where A is slightly larger than M1 and B(approximately-greater-than)0. A discussion of the temperature dependency of the normalized flux creep rate is at the conclusion of the article.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356352
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructure and properties of YBa2Cu3O7−δ thin films with BaO precipitates (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 234-236 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: BaO precipitates with sizes between 10–100 nm in laser ablated YBa2Cu3O7−δ (YBCO) thin films on Y-stabilized Zirconia substrates have been identified by x-ray diffraction and transmission electron microscopy. The precipitates exhibit equiaxed shapes and grow epitaxially inside and on the surface of the YBCO films, with (001)BaO plane parallel to the a,b plane of YBCO. Some of these smaller precipitates and BaO/YBCO boundaries probably provide potential pinning sites for magnetic flux lines, which might contribute to the observed increase of critical current density with magnetic field B under B≤500 G in the case of B perpendicular to the c axis of the film.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112639
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  • 4
    Electronic Resource
    Electronic Resource
    Correlation between distribution of outgrowths and microwave surface resistance for YBa2Cu3O7 thin films (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2356-2358 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model was proposed to describe the effects of surface outgrowths on the microwave surface resistance of high Tc superconducting thin films. Calculated with experimental data the microwave surface resistance at 10 GHz for c-axis oriented YBa2Cu3O7 thin films with no outgrowths could be as low as 70 and 4 μΩ at 77 and 4.2 K, respectively. The effect of the orientation of the surface outgrowths on the microwave loss has been discussed. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112744
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  • 5
    Electronic Resource
    Electronic Resource
    Electron microscopy study of C60 (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 3108-3109 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructural features of the powder C60 material have been studied by using scanning microscopy, electron diffraction, and high resolution electron microscopy. Scanning electron microscopy observation reveals that the grains in the samples are packed by extensively disordered crystallites as well as amorphous granules. Electron diffraction measurements have identified that the crystals of C60 have two kinds of structure, one is face-centered-cubic (fcc) with unit cell parameter a=1.41 nm, and the other has the hexagonal closest packed (hcp) structure with cell parameters a=0.958 nm and c=1.63 nm. High resolution electron microscopy as well as electron diffraction observations clearly show the random crystallites packing in the C60 grains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105779
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  • 6
    Electronic Resource
    Electronic Resource
    Growth and structural analysis of GdBa2Cu3O7 superconducting thin films on MgO single-crystal substrates (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 2320-2322 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of GdBa2Cu3O7 superconductor were grown in situ on MgO single-crystal substrates under different substrate temperatures (Ts). When Ts=800 °C, the films were epitaxially grown with the c axis perpendicular to the film surface. The growth quality was very good, but the zero resistance critical temperature (Tc0) was only 85 K and the transition width (ΔTc) was 1.5 K. When Ts=670 °C, some of the films were epitaxially grown with the c axis perpendicular to the film surface. Some were mainly c axis oriented with a small amount of (110) and a-axis orientation. The growth quality was relatively poor, but they had Tc0 of 89–91 K and ΔTc of 0.6–1 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106056
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  • 7
    Electronic Resource
    Electronic Resource
    Superconductivity of Bi2 (Sr0.9Ca0.1)2 CuO y single crystals (1994)
    Springer
    Applied physics 58 (1994), S. 73-75 
    Details
    ISSN: 1432-0630
    Keywords: 74.62Bf ; 74.25−9
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Bi2 (Sr0.9Ca0.1)2 CuO y single crystals were grown by the self-flux method. The temperature dependence of resistance and ac susceptibility measurements showed that the as-grown crystal is semiconductive between 4.2 K and 300 K. However, after annealing in air for more than 20 days the crystal became superconducting with a T c of 66 K obtained from the R-T curve. The ac susceptibility data also showed a strong superconducting transition at 71 K. X-ray diffraction indicated that the structure of the as-grown and the annealed crystal both are orthorhombic. The T c of 71 K of the Bi2 (Sr0.9Ca0.1)2 CuO y crystal may be due to the increase of oxygen content in the crystal after the long-time annealing in air. It is suggested that the superconductivity of the Ca-doped 2201 phase of the Bi-based system, which up to now was found to have a T c=7–22 K, is similar to the 2201 phase of the Tl-based system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00331520
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  • 8
    Electronic Resource
    Electronic Resource
    Composition and superconductivity in Bi-Sr-Ca-Cu-O and substituted systems (1989)
    Springer
    Journal of materials science 24 (1989), S. 1725-1728 
    Details
    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 composition of the superconducting phase Bi4(Sr3±x Ca3∓x )Σ=6Cu4O16, has been determined by means of a sysmetic investigation of the relationship between composition and superconductivity, and phase analysis. The superconducting phase belongs to tetragonal system witha=0.3825 nm,c=3.082 nm, space group (S.G.) 14/mmm. The effect of strontium and calcium contents in the Bi(Sr1±x Ca1∓x )Σ=2Cu2O5.5, system and substitution in the Bi1−x A x SrCaCu2O5 (A=V, Gd, Y) and BiSrCa1−x Pb x Cu2O5.05 systems on superconductivity, have been investigated. In the Bi-Sr-Ca-Cu-O system, there are two superconducting phases corresponding to transition temperatures of 110 and 80 K, respectively. The difference between the two superconducting phases may be due to the stacking difference of atoms along thec direction in the structure and their oxygen content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01105697
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  • 9
    Electronic Resource
    Electronic Resource
    The crystal structure and superconductivity of the new superconducting phase TlSr2Ca0.5Er0.5Cu2O6.75 (1989)
    Springer
    The European physical journal 76 (1989), S. 277-281 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The crystal structure of the superconducting phase TlSr2Ca1−xErxCu2O6.5+x/2 (x=0.5) in the Tl−Sr−Ca−Er−Cu−O system was determined using the X-ray powder diffraction method. It belongs to a primary tetragonal cell with lattice constantsa=3.798,c=12.014 Å, with a space group ofD 4h 1 −P4/mmm. Each unit cell contains one formula unit. The positions of ions in the unit cell are as follows: 0.5 Ca and 0.5 Er cations disorderly occupy 1(d) equivalent point position, each with an occupation factor of 0.5; 1. Tl cation occupies the equivalent point position 1 (a); 2. Cu cations occupy 2 (g) withz=0.365; 2 Sr cations occupy 2(h) withz=0.220; 7 O anions respectively occupy 1(c), 2(g), (z=0.165) and 4(i) (z=0.365) equivalent point positions. The zero-resistance superconducting transition temperatureT c (0) decreased slightly with increased Er content in the Tl−Sr−Ca−Er−Cu−O system. The crystal structure of TlSr2Ca0.5Er0.5Cu2O6.75 is very similar to that of TlBa2CaCu2O6.5 in the Tl−Ba−Ca−Cu−O system or RBa2Cu3O7 in the R−Ba−Cu−O system. In the superconducting phase with an oxygen-deficient perovskite-like structure, the similarity of cation-oxygen coordination polyhedra is important for cation substitution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01321903
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  • 10
    Electronic Resource
    Electronic Resource
    Modulated structure of the superconducting compounds Bi2Sr2Ca n-1Cu n O y withn=1 and 2 (1989)
    Springer
    The European physical journal 74 (1989), S. 165-172 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The incommensurate modulated structures of high-T c superconducting phases Bi2Sr2Ca n−1Cu n O y (n=1 and 2) have been studied using symmetry properties of four-dimensional super-spacegroups and electron diffraction as well as high resolution electron microscopy are used to describe the properties of the incommensurate modulated structure in the compounds. The main results are planar monoclinic symmetryP B 2/b 11 orP B b 1 for Bi2Sr2CuO y (n=1) and orthorhombic symmetryN 111 Bbmb orN 111 Bb2b for Bi2Sr2CaCu2O y (n=2). The temperature dependence of the modulated structure of Bi2Sr2CaCu2O y has been investigated from −190°C to 800°C. Some structure properties of Bi2Sr2Ca2Cu3O y (n=3) are presented for comparison.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307382
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