Flux Pinning Behavior Research Articles

The effect of Er-substitution on the superconducting properties of MTG-YBaCuO crystals

The high quality Er-doping Y0.8Er0.2Ba2Cu3O7−δ (YErBCO) crystal is grown by the melted-textured-growth (MTG) method. The microstructure photograph shows that the MTG-YErBCO crystal has an obvious layered structure. Its magnetization loops show that the irreversibility field is decreased by Er-doping for H//c and that there is an anomalous behaviour, a second peak, in the magnetization curve for H//ab. The critical current density along the ab-plane (Jcab(77 K, 0 T) = 4.75 × 104 A cm−2) is higher than that along the c-axis (Jcc(77 K, 0 T) = 470 A cm−2). The field dependence of the irreversibility temperature Tirr follows a power law, H = H0(1 − Tirr(H)/Tirr(0))1.3, with H0 = 550 T for H//ab and 51 T for H//c, respectively. The field dependence of the activation energy Ue shows a different behaviour for H//ab and for H//c, namely a linear relation, U = 49131–3006H, for H//ab and a power law, U ∝ H−0.68, for H//c, respectively. The anisotropy factor γ = 15 was obtained from the angular dependences of the activation energy and the irreversibility temperature. A possible reason for the effect of Er addition on the flux-pinning behaviour has been discussed.

Flux-pinning behavior and the interlayer coupling of theHg0.7Cr0.3Sr2CuO4+δsuperconductor

Flux-pinning behavior and the interlayer coupling of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Hg</mml:mi></mml:mrow><mml:mrow><mml:mn>0.7</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cr</mml:mi></mml:mrow><mml:mrow><mml:mn>0.3</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Sr</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CuO</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn><mml:mo>+</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>superconductor

Chromium clustering and ordering in Hg1-xCrxSr2CuO4+ delta.

Solid-solution compounds where Cr, Re, and other metals are substituted for Hg in Hg-Ca-Ba-Cu-O superconductors have been reported to exhibit enhanced flux-pinning behavior. We have determined the structural modifications resulting from the incorporation of Cr in Hg{sub 1{minus}{ital x}}Cr{sub {ital x}}Sr{sub 2}CuO{sub 4+{delta}} (for {ital x}{approx}0.4) using neutron powder diffraction, electron diffraction, and lattice imaging. Cr substitutes at the Hg site, but is displaced to allow tetrahedral coordination by oxygen atoms. Additional oxygen is incorporated to provide four oxygen atom neighbors for each Cr atom. These CrO{sub 4} units cluster to form a supercell of approximate dimensions 5{ital a}{times}5{ital a}{times}2{ital c} in which Cr-rich and Hg-rich regions alternate in all three crystallographic directions. Because the Cu-O apical bond associated with the CrO{sub 4} unit is lengthened to 3.13 A, the superconducting planes are best viewed as consisting of CuO{sub 5} pyramids, oriented up or down as dictated by the supercell ordering, rather than CuO{sub 6} octahedra. Local structural constraints associated with individual Cr sites require that considerable disorder is present, even in the supercell. Extended defects in this supercell (e.g., columns of CuO{sub 6} octahedra associated with Hg-rich regions) may contribute to the enhanced flux pinning.

Irreversibility lines and critical current densities of PMP-processed YBCO

Two PMP-processed YBCO specimens fabricated at different melting temperatures were investigated. The critical current density (Jc) was determined from flux-profile measurements. One sample was re-annealed at 880 degrees C for 30 hours to reduce the number of stacking faults and dislocations. The Jc values and irreversibility lines of this sample were measured before and after re-annealing. The results indicate that stacking faults and dislocations strongly influence the flux-pinning behaviour of PMP-processed YBCO superconductors.

Melt-processing of YBa/sub 2/Cu/sub 3/O/sub x/ and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/: influence of processing parameters on microstructure and magnetization behavior

An investigation of the flux-pinning behavior of melt-processed YBa/sub 2/Cu/sub 3/O/sub x/ and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ has been carried out by means of microstructural investigations and magnetization measurements. It was found that both microstructure and magnetization behavior strongly depend on the chemistry and the grain size of the starting material. The carbon content and the melting behavior of the YBa/sub 2/Cu/sub 3/O/sub x/ powders seem to play an important role in the development of microstructure and flux-pinning behavior during melt-texturing. Carbon, which is existing in different amounts in all commercially available YBa/sub 2/Cu/sub 3/O/sub x/ powders and is also easily introduced during processing, was found to have the same detrimental influence on the grain boundaries of melt-processed materials as on the grain boundaries of sintered pellets. On the other hand an increase in the flux-pinning behavior could be found when carbon was present during the melting and resolidification process. Our results indicate that the presence of carbon during the resolidification process results in the incorporation of precipitates and defects not only into the grain boundaries, but also into the bulk of YBa/sub 2/Cu/sub 3/O/sub x/ leading to an increased intragrain critical current density. Initial experiments indicate that a similar effect might also be possible for Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/. >

Cation nonstoichiometry in (Bi, Pb) 2Sr 2Ca 2Cu 3O 10+δ

X-ray lattice parameter measurements of the (Bi, Pb) 2- x Sr 2- y Ca 2- z Cu 3O 10+δ system show that a continuously varying solid-solution cation nonstoichiometry exists within -0.1< x<0.1, 0< y<0.3, and 0< z<0.3. However, the system cannot incorporate any defect at its Cu site. The oxygen content determined by titration decreases linearly with increasing cation-vacancy concentration. The critical temperature, T c, shows a maximum value at the stoichiometric cation composition and decreases to a lower constant value across the nonstoichiometric composition region with increasing alkaline-earth deficiency. Flux pinning in this system is increased by the cation-vacancy concentration only in the low-temperature range, while it decreased in the high-temperature range. The flux-pinning behavior is discussed in view of its two-dimensionality in the superconductivity for this system.

Structural and chemical disorder near the Y2BaCuO5/YBa2Cu3O7- delta interface and its possible relation to the flux-pinning behavior in melt-textured YBa2Cu3O7- delta.

©1993 The American Physical Society. The electronic version of this article is the complete one and can be found online at: http://link.aps.org/doi/10.1103/PhysRevB.47.5373

Flux creep and pinning potential distribution in zone-melted YBa2Cu3Ox

Magnetic relaxation data have been taken on zone-melted and sintered YBa2Cu3Ox samples over wide temperature and magnetic field ranges. We have found that magnetic relaxation varies greatly in the samples with different microstructures and crystallographic orientations. Flux-creep rates have been found to be reduced in the zone-melted samples owing to large amounts of intragranular crystal defects such as edge dislocations and stacking faults. An important flux-pinning behavior related to the pinning potential distributions has been observed in the samples. The relationship between microstructural orientation and pinning potential distributions in YBa2Cu3Ox is discussed.

Is J&amp;lt;inf&amp;gt;c&amp;lt;/inf&amp;gt;in Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Sn limited by grain-boundary flux-shear?

It is postulated that flux-pinning by grain-boundaries may be avoided if flux can shear and flow down paths lying in grain-boundaries. The difference in flux-pinning behaviour between NbTi, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F_{p}\alpha b(1-b)</tex> , and solid state reacted Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F_{p}\alpha b^{\frac{1}{2}} (1-b)^{2}</tex> , arises from the different morphologies of their grain-structures. The boundaries, drawn out parallel to filament axes and direction of current flow in NbTi act as effective barriers to flux motion. The boundaries of grain produced by reaction in Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn provide paths along which flux can flow by grain-boundary shearing. An expression is developed for grain-boundary shearing which gives good agreement with experimental results.

Flux-pinning and inhomogeneities or defects in amorphous superconducting Mo 5Ge 3 films

An investigation to relate flux-pinning behavior in amorphous thin films of Mo 5Ge 3 to their inhomogeneities or defects has been conducted. The amorphous Mo 5Ge 3 (a-Mo 5Ge 3) films were synthesized at room temperature (RT) and liquid nitrogen temperature (77°K) by magnetron sputtering. A-Mo 5Ge 3 films deposited at RT showed larger pinning force F p than those deposited at 77°K. For a-Mo 5Ge 3 films deposited at 77°K, F p was analyzed according to the theory of Larkin and Ovchinnikov for collective pinning in two dimensions. The temperature scaling law has been observed for a-Mo 5Ge 3 films with different thermal histories.