Distribution of inhomogeneities across the ceramic core in monocore (Bi,Pb)-2223/Ag tapes

Measurements of the critical current dependence on the angular orientation of the applied magnetic field for (Bi, Pb)2Sr2Ca2Cu3O10 (BSCCO-2223)/AgMg-sheathed, mono-core BSCCO-2223/Ag-sheathed and Bi2Sr2CaCu2O8 (BSCCO-2212) dip coat tapes are presented. We have demonstrated that the procedure of measurement is an important factor for the angular effect to show. For a magnetic field only applied during the measurement of Ic(θ) (during the rotation the magnetic field is set to zero) we have found a symmetric curve, while when the magnetic field is applied during the rotation the curve is asymmetric. Moreover, we found a large difference in the critical current value between the different procedures. From our measurements, we imply two conditions are necessary to have an angular effect: (1) the magnetic field must be applied during the rotation and (2) we have to start the rotation for a magnetic field parallel to the c-axis. The results are discussed in the context of the accommodation of vortices to planar defects and surface pinning.

Section: Methodsmentioning

confidence: 99%

Angular effects of transport critical currents in high-temperature superconductor tapes

Warmont

Jones²

2001

“…As reported here, besides the 'phase' inhomogeneity within the MgB 2 core, significant 'macrostructural' inhomogeneity also exists. As reported, TAR leads to the best grain connectivity [13,20,[24][25][26]. However, due to the high scatter in the sizes (0.1-60 µm) of MgB 2 grains and agglomerates and the uneven hardness distribution within the cores, the investigated square wires are characterized by high inhomogeneity across their width and along their length.…”

Section: Resultsmentioning

confidence: 78%

Structural inhomogeneity of superconducting ex situ MgB2/Cu wires made by the powder-in-tube technique

Pachla

Presz

Diduszko

et al. 2002

Self Cite

Single core MgB 2 wires have been made by the powder-in-tube (PIT) method using commercial MgB 2 powder (Alfa Aesar). Using the two-axial rolling process, composites have been made in a Cu sheath. Energy dispersive x-ray (EDX) mapping and scanning electron microscopy backscattered electron observations prove that there is high element segregation (phase inhomogeneity) for as-rolled and as-sintered wires, although the wire after sintering is more inhomogeneous than the as-rolled (non-sintered) wire. X-ray diffraction diffractograms confirm the presence of isotropy and the absence of texturization in the 'macroscopic' phase within the MgB 2 cores, despite their thermomechanical history. The observed decrease in the value of J c in the wire after sintering was attributed to macroscopic cracking and the worsening of the intergrain connectivity. EDX line scans have also shown high anisotropy and high inhomogeneity in the distribution of elements within the MgB 2 cores. Inhomogeneity in the final product (wires) has resulted from the high macroscopic inhomogeneity observed in the starting MgB 2 powder. The Cu sheath has been shown to be neutral (non-poisoning) for MgB 2 cores made ex situ. However, due to its softness, it cannot properly constrain the MgB 2 core or give enough support required for adequate grain connectivity.

“…They are more pre-reacted (by ∼5% higher 2223 content) resulting in a higher degree of texturization (FWHM) and confirming the commonly reported better texturization for a higher ratio of the matrix/ceramic interface to the ceramic volume. However, it must be remembered that the situation below the matrix/ceramic interface may differ significantly [14] from that observed at the surface, since x-ray penetration is approximately 10 µm below the investigated surface (for an x-ray beam perpendicular to the ceramic surface) and the evaluated FWHM are not representative for the layers closer to the centre of the tape.…”

Section: Resultsmentioning

confidence: 98%

Effect of starting precursor onI_canisotropy in powder-in-tube (Bi, Pb)2223/Ag tapes

Pachla

Kòváč

Hušek

et al. 2001

Self Cite

Two powder precursors, differentiated by their average grain size, have been applied to the manufacture of monocore and 19-filament Bi(2223)/Ag tapes by the powder-in-tube (PIT) method. The optimized PIT route has been applied for each precursor. The influence of both precursors on the I c anisotropy and critical current density J c in the final tapes have been studied. The transport current properties are related to grain morphology and texturization of both materials. Finer starting precursor has led to much higher I c anisotropy and to better bulk texturization of the ceramic cores resulting in higher J c .