Evolution of the transport critical current density and irreversibility field as a function of heat treatment and pressing pressure during processing of Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes

Abstract

Extended electric field-current density characteristics taken on the bare cores of monofilament ͑Bi,Pb͒ 2 Sr 2 Ca 2 Cu 3 O x ͑2223͒ tapes at 77 K have been used to measure the irreversibility field, H*, and the critical current density, J c , at different stages of tape processing. The number of heat treatments and the uniaxial pressing pressure were the experimental variables. Both H* and J c increased substantially with heat treatment and with deformation pressure. The data are consistent with an improvement in J c from two factors, one being an increase in the 2223 phase fraction with increasing heat treatment, the second, independent cause being an increase in the flux pinning properties of the composite. The experiments show that improving J c involves control of at least three factors: enhancing the volume fraction of 2223 phase; increasing flux pinning; and enhancement of the connectivity of the grain boundaries that lie within the current path. © 1997 American Institute of Physics. ͓S0021-8979͑97͒00705-6͔

Determination of irreversibility field variations in mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox tapes by transport current methods

“…To keep thermoelectric noise at a minimum, continuous Cu leads were used from the voltage contacts on the sample to the inputs of the nanovolt preamplifier. It has been shown previously 8,9,14 that there is some current sharing by the silver sheath in electric fields greater than 1 V/cm. Therefore, in method 1, to correct for this sharing, we subtracted the effect of the silver using a method described in an earlier work.…”

“…In method 1 ͑the E -J curvature method͒, extended electricfield (E) -current-density (J) characteristics were measured and each extended log(E)-log(J) curve was fit to a quadratic equation. H* was then defined as the field at which the curvature changes from negative to positive, 1,[8][9][10]13,14 as shown in Fig. 1.…”

“…However, J c (B) is strongly influenced by the strength of the flux pinning. At high fields, either intragranular [1][2][3][4][5][6] or intergranular 7,8 flux pinning becomes the main J c -limiting mechanism. Because different mechanisms determine J c (0) and J c (B), this leads us to believe that J c (B) may be optimized independently of J c (0).…”

“…H* can be measured by several magnetization and transport current techniques. Previous work [8][9][10] has shown that individual composites often show a direct correlation between H* and J c (0). However, as we have accumulated a larger database of H* and J c (0) characterizations, we have found that there is no universal correlation and we, therefore, conclude that it is vital to characterize both the flux pinning and zero-field properties, if the highest performance is to be developed in BSCCO-2223 tapes.…”

The use of the in-field critical current density, Jc(0.1 T), as a better descriptor of (Bi, Pb)2Sr2Ca2Cu3Ox/Ag tape performance

“…H* was found by examining the V -I curves and determining the field at which the curvature changed from positive to negative. 12,13 I c (H) was extracted from the V -I curves using a criterion of 1 V/cm. J c (H) is defined in this letter as I c /A, where A is the average of two or three ͑Bi, Pb͒2223 cross sections.…”