Critical currents in Ag/Bi-2223 superconducting tapes: grain connectivity and flux pinning

Horvat, J.; Wang, W.G.; Bhasale, R.; Guo, Yuan; Liu, H.K.; Dou, Shi Xue

doi:10.1016/s0921-4534(97)00012-9

Cited by 26 publications

(8 citation statements)

References 21 publications

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“…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).…”

mentioning

confidence: 99%

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

Anderson

Parrell

Polák

et al. 1997

Applied Physics Letters

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The irreversibility field, H*, has been measured for a variety of mono-and multifilamentary ͑Bi,Pb͒ 2 Sr 2 Ca 2 Cu 3 O x ͑2223͒ tapes using two different transport current techniques. It is common to characterize the quality of 2223 tapes by their zero-field, 77 K critical current density ͓J c (0 T, 77 K͔͒, even though this ignores the fact that significant self-fields depress J c (0 T, 77 K) and the possibility that the in-field J c (B) characteristics may be optimized independently of the J c (0 T, 77 K) value. To provide more useful information, we propose a second characterization, that of the irreversibility field, H*. Having both H* and J c (0 T, 77 K) information helps in separating the two independent contributions that better connectivity and stronger flux pinning can make to the J c of a tape. We illustrate this point with results from a variety of mono-and multifilamentary Bi-2223/Ag tapes in damaged and undamaged conditions, which show that H* ͑77 K͒ can vary from ϳ100 to ϳ200 mT and not directly correlate with J c (0 T, 77 K). The two proposed protocols for H* measurement are robust and compatible with common transport measurement procedures. © 1997 American Institute of Physics. ͓S0003-6951͑97͒00352-5͔Both the zero-field, J c (0), and the in-field, J c (B), critical current densities of ͑Bi,Pb͒ 2 Sr 2 Ca 2 Cu 3 O x ͑2223͒ tapes must be improved to make applications economically feasible. J c is defined experimentally as J c ϭI c /A where I c is the critical current and A is the area of the whole ceramic cross section. However, this averaged, overall J c is most certainly an understatement of the maximum local J c because the current percolates through only a fraction of the cross-sectional area, A active . J c (0) contains significant contributions from current paths that include weakly linked grain boundaries, which are decoupled by small magnetic fields, and it is thus at least partially limited by self-fields generated by the transport current. However, J c (B) is strongly influenced by the strength of the flux pinning. At high fields, either intragranular 1-6 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). The irreversibility field, H*, is an increasingly common parameter used to measure flux pinning because it is strongly influenced by flux pinning. 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.When H* is measured by magnetization, the magnetization signal is averaged ov...

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confidence: 99%

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

Anderson

Parrell

Polák

et al. 1997

Applied Physics Letters

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“…This will be beneficial to flux pinning in the tapes. : is the critical current through strong links [9] at zero field. These two ta,pes show 34% and 41% of 1 , : /Ico respectively.…”

Section: Resultsmentioning

confidence: 99%

Effect of cryogenic deformation on microstructure and critical current density in Ag/Bi-2223 tapes

Liu

Liao³

et al. 1999

IEEE Trans. Appl. Supercond.

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Abstracts-The effect of deformation rate and silver hardness on .I, a n d microstructure of Ag/Bi-2223 tapes was studied under cryogenic processing conditions. It was found that cryogenic deformation improved the grain connectivity, alignment, Adcore interface and critical current density. These benefits may be attributable to the increased extent of mechanical deformation. The hardness of silver sheath during cryogenic mechanical deformation was significantly increased, allowing for a much larger load to be applied during the deformation process comparing to the mechanical deformation at room temperature. The maximum J, appeared at a 20% reduction rate of the tape thickness for cryogenically processed Ag/Bi-2223 tape. Higher deformation rate decreases J, for cryogenically processed Ag/Bi-2223 tape which can be explained by the results of TEM examination. TEM images show that the sample having low J, had many small grains with large angle grain boundaries after recrystallisation when high rate of thickness reduction (58%) was applied during the process, while the sample having high J, had large grain with many small angle c-axis twist grain boundaries and small angle tilt grain boundaries when 19% of thickness reduction was applied during the process.However, our recent work on systematic comparison of HTSC samples, prepared by using different deformation process has revealed an interesting phenomenon between the effects of hot-and cold (i.e. ambient temperature) deformation. We discovered that whereas hot deformation improves the weak links, samples prepared by using cold deformation process show an improved flux pinning. For example, the irreversibility lines and magnetisation hysteresis loops for the cold processed AgIBi-2223 tapes exhibit stronger pinning than for the hot deformed tapes [4]. These findings have led to the new concept of cryogenic deformation or supercold deformation [SI. Furthermore, silver becomes very soft at high temperatures, causing sausaging effect during hot deformation, in particular hot-rolling.Preliminary results show the cryogenic deformation improved the microstructure and critical current density [6]- [7]. However, the mechanism of the improvement is unclear. In this paper, we report the results of silver hardness measurements and effect of deformation rate on microstructure of cryogenic deformed tapes.

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“…Mechanical damage can affect the weak links versus the strong links to a different extent, which can be revealed in the change of the field dependence of I c [15]. The critical current through strong links in zero field (I s c0 ) can be obtained by extrapolating I c against H at elevated fields to zero field (figure 1) [16]. The value of I s c0 /I c0 can then be used to monitor the change of the strong-link connectivity as the tape is increasingly damaged.…”

Section: Resultsmentioning

confidence: 99%

Effects of mechanical deformation on critical current of Bi-2223/Ag tapes

Horvat

Guo

Bhasale

et al. 1998

Supercond. Sci. Technol.

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The influence of mechanical deformation on critical current has been studied, in order to assess the effect of sample handling on the current carrying capabilities of Bi-2223/Ag tapes. Transport critical current was measured at 77 K using a criterion. The effect of progressive bending of the tapes on grain connectivity and flux pinning were investigated by measuring against H. It was observed that bending can affect weak and strong links to a different degree. Damaged samples have a low , but often have a large critical current which is carried through strongly linked paths, compared to carried through weak links. The influence of tensile deformation on was also studied. was found not to degrade until the deformation of the tape approached its elastic limit.

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Critical currents in Ag/Bi-2223 superconducting tapes: grain connectivity and flux pinning

Cited by 26 publications

References 21 publications

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

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

Effect of cryogenic deformation on microstructure and critical current density in Ag/Bi-2223 tapes

Effects of mechanical deformation on critical current of Bi-2223/Ag tapes

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