• S R Shukla

      Articles written in Pramana – Journal of Physics

    • Role of processing in improving the critical current of Ag/BPSCCO tapes

      S R Shukla Y S Reddy D K Pandya Y Tanaka R G Sharma

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      Silver-clad tapes of highTc Bi-Pb-Sr-Ca-Cu-O superconductors have been fabricated through the powder-in-tube method. The critical current density, Jc, of a thick tape was 534 A.cm−2 (77 K, 0 T). Subsequent rolling and sintering of the tapes led to a gradual decrease inJc, instead of the expected increase. This was caused by the microcracks developed in the core material by a rather drastic reduction during the rolling of the tapes. A modified and well controlled rolling technique, on the other hand, resulted in much improvedJc values. Repeated rolling and sintering resulted in a good grain alignment and no microcracks were observed. In the present studies, maximumJc of 1846 A.cm−2 (77 K, 0 T) and 2.43 × 104 A.cm−2 (4.2 K, 0 T) have been obtained Optimization of the processing and sintering parameters are expected to lead to still higherJc values.

    • Critical current in Ag/BPSCCO tapes using low purity materials

      S R Shukla Y S Reddy R G Sharma

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      Silver-clad Bi1·7Pb0·4Sr1·8Ca2Cu3·5Ox (BPSCCO) tapes have been fabricated using low purity (98–99%) starting materials and following the powder-in-tube technique. MaximumJc values of 6·14 × 103 A·cm−2 at 77 K and 1·4 × 105 A·cm−2 at 4·2 K have been obtained in tapes subjected to the process of intermediate rolling and sintering. The bulk superconducting material used for the tape-fabrication contains both 2223 and 2212 phases in the ratio 60:40. A pure phase material and the optimization of the sintering parameters are expected to yield much higherJc values at 77 K. It is possible that the copper-rich phase(s) and/or a small amount of iron impurity (60 ppm) present in CuO might be acting as flux pinning sites and could be responsible for highJc values.

    • Further studies on Ag/BPSCCO tapes using low purity materials

      S R Shukla Y S Reddy N Kumar S K Sharma R G Sharma

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      Transmission electron microscopic (TEM) studies are reported on Ag-clad Bi1.7 Pb0.4Sr1.8Ca2Cu3.5Ox tapes prepared by using low purity (98–99%) commercial grade materials. The self-fieldJc values of these tapes viz. 6.14 × 103 A.cm−2 at 77 K and 1.4 × 105 A.cm−2 at 4.2 K, reported in an earlier publication, were significantly higher than the correspondingJc values in tapes prepared with high purity (99.99%) materials. The TEM pictures on the low purity core material of the tapes reveal the presence of stacking faults and the intergrowth of the 2212 and 2223 phases which could be acting as flux pinning sites and responsible for enhancedJc values. These defects can perhaps be traced back to the presence of 60 ppm iron in the low purity CuO as revealed by atomic absorption analysis reported earlier.

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