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  • 1
    Electronic Resource
    Electronic Resource
    Plastic deformation in high critical current melt-textured YBa2Cu3O7 (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5515-5517 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of high-temperature creep under different conditions in melt-textured YBa2Cu3O7–Y2BaCuO5 composites, with high critical currents before deformation, is investigated. Transmission electron microscopy studies show that the low-temperature oxygenation process causes a strong modification of the as-deformed microstructure and leads to a clear degradation of the superconducting performances. This behavior of the superconducting properties is well correlated with the formation of extended planar defects such as large stacking faults and microcracks that severely diminish the vortex cutting length, thus enhancing the thermal activation effects on the critical currents and the irreversibility line. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363484
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  • 2
    Electronic Resource
    Electronic Resource
    X-ray study of the three-dimensional orientation of mixed a/c-oriented YBa2Cu3Ox films on (100)-SrTiO3 substrates by metalorganic chemical vapor deposition (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2951-2953 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-dimensional x-ray diffraction study of films deposited on (100)-SrTiO3 substrates by metalorganic chemical vapor deposition at two substrate temperatures is reported. Films deposited at 740 °C contain domains with either the a, b, or c axes perpendicular to the substrate, while those grown at 810 °C display almost only c-axis orientation. The 〈110〉 in-plane directions of the substrate and the c-axis oriented grains are aligned, while a/b-axes oriented grains have their [001] and [010]/[100] directions aligned with the substrate 〈100〉 ones. The in-plane mosaic spread is smaller for higher deposition temperatures. We demonstrate that the films are densely twinned independently of the orientation of the coexisting domains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357534
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  • 3
    Electronic Resource
    Electronic Resource
    Polygonization of directionally solidified high critical current YBa2Cu3O6+x (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8847-8849 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mosaic structure of single domain YBa2Cu3O6+x/Y2BaCuO5 (123/211) directionally solidified composites is investigated by x-ray diffraction and transmission electron microscopy. This mosaic structure results from a polygonization process before the oxygenation step. A topological model is given based on the observed distribution of preferred subgrain boundary planes. This polygonization, characteristic of melt textured 123, is proposed to be an intrinsic critical current density limitation for these materials. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362476
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  • 4
    Electronic Resource
    Electronic Resource
    X-ray diffraction studies of the epitaxy of a/b-axes oriented YBa2Cu3O7−δ films grown by liquid phase epitaxy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5243-5248 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed x-ray diffraction study is reported for a/b-axes oriented YBa2Cu3O7−δ films obtained by the liquid phase epitaxy technique. The films were grown epitaxially in the tetragonal state on (110) NdGaO3 substrates so that [001]film(parallel) [110]subs and [100]film(parallel) [001]subs, 90°-[100]/[010] boundaries were almost absent. Below the tetragonal-to-orthorhombic transition temperature, the film undergoes intensive {hh0}-type twinning. The volume of the a-axis oriented material is similar to that of the b-axis oriented fraction and the presence of both orientations is likely to be controlled by {hh0}-type twinning. High temperature diffraction of the substrate indicates that nucleation of YBa2Cu3O7−δ on (110) NdGaO3 takes place on a square two-dimensional lattice and therefore the observed strong in-plane alignment is probably controlled by impurity action and/or surface relaxation rather than simple mismatch effects. The difference between the thermal expansion coefficients of the film and the substrate (αfilm[100], αfilm[010](approximately-greater-than)αsubs[001]) is compensated for upon cooling by a slight rotation (ε∼0.12°) of {hh0}-type domain boundaries around the common [001] direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355722
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  • 5
    Electronic Resource
    Electronic Resource
    Enhanced critical currents in melt textured YBa2Cu3O7 by cold isostatic pressing (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 73-75 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An enhancement of the critical currents in the H||c configuration, reaching 100% at 77 K, has been obtained in melt textured YBa2Cu3O7/Y2BaCuO5 composites after a cold isostatic pressing process (300 °C, PAr=200 MPa). A transmission electron microscopy analysis of the microstructure demonstrates that a high density of nanometric stacking fault loops, with anisotropic growth within the (001) plane, is generated. The improvement of critical currents is attributed to the flux pinning enhancement due to the increased length of the 1/6〈031〉 partial dislocations surrounding nanometric stacking faults. We stress that this technique has high potential for the large scale processing of high critical currents superconducting ceramic composites. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122955
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  • 6
    Electronic Resource
    Electronic Resource
    Stability and evolution of stacking faults in melt textured YBa2Cu3O7−x (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2192-2194 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The annihilation process of large 〈fraction SHAPE="CASE"〉16〈301〉 stacking faults in melt textured YBa2Cu3O7−x is in situ monitored in the transmission electron microscope. The process is activated at the onset of the orthorhombic to tetragonal transition induced in the electron microscope, thus evidencing the instability of such defects in the deoxygenated YBa2Cu3O7−x matrix. The observations suggest that the annihilation (and growth) process is limited by surface diffusion along Y2BaCuO5/YBa2Cu3O7−x interfaces. The propagation mechanism of such stacking faults is addressed in the light of the present findings. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119038
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  • 7
    Electronic Resource
    Electronic Resource
    Enhanced critical currents by CeO2 additions in directionally solidified YBa2Cu3O7 (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1448-1450 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure and critical currents of superconducting YBa2Cu3O7-Y2BaCuO5 composites with small CeO2 additions prepared using a directional solidification procedure have been investigated. The small CeO2 additions cause the decomposition of the Y2BaCuO5 phase leading to the formation of Y2O3 and BaCeO3. Experimental evidence is given for the subsequent nucleation of the Y2BaCuO5 phase on the Y2O3 particles. This new decomposition-nucleation mechanism leads to textured YBa2Cu3O7 having enhanced critical currents. An addition of 0.3 wt % CeO2 can increase Jabc by a factor of 2 in samples having similar concentration of Y2BaCuO5 precipitates. Critical currents above 105 A/cm2 at 77 K and zero field are obtained by this method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112011
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  • 8
    Electronic Resource
    Electronic Resource
    Aging of critical currents and irreversibility line in melt textured YBa2Cu3O7 (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 772-774 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The critical currents and the irreversibility line of bulk melt textured YBa2Cu3O7 have been found to evolve with the increase of the oxygenation time. A strong field-dependent reduction of the critical currents is observed which finally leads to a downward shift of the irreversibility line. Transmission electron microscopy micrographs of aged samples display a huge increase in the concentration of stacking faults near the microcracks and at the YBa2Cu3O7-Y2BaCuO5 interfaces. Low field ac susceptibility measured with H(parallel)ab shows a strong reduction of the screening capability thus meaning that nonsuperconducting planar defects parallel to the ab planes have been created. We suggest that an enhanced two-dimensional behavior of the vortex flux lattice occurs when H(parallel)c as a consequence of this layered defective structure. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114089
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  • 9
    Electronic Resource
    Electronic Resource
    Three dimensional dislocation substructure in NdBa2Cu3Oy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2660-2662 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three dimensional dislocation substructure is reported by transmission electron microscopy in an as-grown directionally solidified (rare earth) Ba2Cu3Oy superconductor. Dislocations with a near or perfect [001] orientation and Burgers vectors lying on the basal plane are found to glide on (010) and {110}. A model is proposed in which cubic-like glide is achieved through the formation of a track of Nd→Ba antisites along the path swept by the dislocations. This finding can be correlated with the enhanced flux pinning under H||[001] observed in these materials. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122545
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  • 10
    Electronic Resource
    Electronic Resource
    Interface pinning in high Tc-high Jc Nd1+xBa2−xCu3Oy directionally solidified in air (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 413-415 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single domain bars of NdBa2Cu3O7/Nd4Ba2Cu2O10 (Nd123/422) superconducting composites have been fabricated in air by using a directional solidification technique. Tc values of 96.5 K can be obtained after an Ar heat treatment and further oxygenation thus showing that reduced oxygen partial pressure during solidification is not a fundamental requirement to prepare high-Tc Nd123 bulk superconductors. The temperature dependence of the critical currents point to a limited efficiency of the Nd123/422 interfaces to pin vortices. High resolution electron microscopy observations clearly reveal smooth Nd123/422 interfaces thus suggesting that interface pinning may not be as relevant as compared to Y123/211 composites. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119326
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