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  • 1
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.349695
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  • 2
    Digitale Medien
    Digitale Medien
    Effect of structure and morphology on resistive loss at 10 GHz of the large-area laser-deposited YBa2Cu3O7 thin films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1165-1170 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Three large-area YBa2Cu3O7(YBCO) superconducting thin films have been laser-deposited under almost identical conditions. However, the microwave surface resistance Rs of the films deviated greatly, they are 280 μΩ, 3.78 mΩ, and 97 mΩ, respectively. It was found that the structure and morphology of the films greatly influence the resistive losses at 10 GHz and 77 K of the YBCO thin films. Different loss mechanisms were discussed. For high Rs, the large angle grain boundaries were the dominate defect in the thin films and increased the Rs of the film markedly. For low Rs, it was mainly due to the misaligned "123'' grains in the thin films and the intrinsic loss. For Rs up to the mΩ range, besides the misaligned 123 grains, domain boundaries and nonsuperconducting outgrowths of different sizes appeared and this caused the rise of Rs value. All these results were given experimentally and discussed theoretically. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.358981
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  • 3
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.356352
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  • 4
    Digitale Medien
    Digitale Medien
    An ion-beam-assisted process for high-Tc Josephson junctions (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 2373-2375 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have developed a non-ion-etching ion-beam-assisted-deposition (IBAD) process for fabricating high critical-temperature (Tc) grain boundary Josephson junctions through a photoresist liftoff mask. The YBa2Cu3O7 (YBCO) junctions fabricated through this process exhibited the resistively-shunted-junction (RSJ)-like I–V characteristics. The well-defined Shapiro steps have been seen on the I–V curves under microwave radiation. The magnetic modulation of critical current of a 4 μm width YBCO junction tallied with the prior simulated Fraunhofer diffraction pattern of a Josephson junction with a spatially homogeneous critical current density. The maximum peak-to-peak modulation voltage across the dc superconducting quantum interference device (SQUID) fabricated by using these junctions reached up to 32 μV at 77 K. The magnetic modulation of the SQUID exhibited periodic behavior with the observed modulation period of 5.0×10−4 G. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.120031
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  • 5
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.112639
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  • 6
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.112744
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  • 7
    Digitale Medien
    Digitale Medien
    Microstructural features at the interface between laser ablated YBa2Cu3O7 films and LaAlO3 substrates (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 3356-3358 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The microstructure at the interface between YBa2Cu3O7(YBCO) thin film and (100)LaAlO3 substrate has been investigated by using transmission electron microscopy. It has been observed that two distinct microstructural features existed in the interface: (1) A thin transitional layer of Ba3Al2O6 was frequently observed and the YBCO thin film grown on it showed stacking faults. (2) Sharp interface with no transitional layer was also occasionally observed and the YBCO film grown on it was single crystalline. In rare cases, a low symmetry phase was observed near the surface of the LaAlO3 substrate, however, the distortion caused by the lattice mismatch between this phase and the YBCO did not affect the quality of the YBCO thin film. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.113756
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  • 8
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.105779
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  • 9
    Digitale Medien
    Digitale Medien
    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
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.106056
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  • 10
    Digitale Medien
    Digitale Medien
    Further development of a novel pulling device for crystal growth (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 1585-1586 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We have proposed a new method that could increase the pulling stroke length in a thermal expansion pulling device used for crystal growth. In this method, the thermal expansion part consists of more than one expansion rod linked by materials with low thermal expansion coefficients. We have constructed an experimental setup to demonstrate the advantage of the new design over the previous one. The measured data showed that the stroke length can be increased by 40% with two expansion rods. Also, a linear temperature dependence of the length was observed, and the reason for this observation was discussed. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1333039
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