Effect of sintering periods on the microstructure and electrical transport properties of high-Tc superconducting Bi–(Pb)–Sr–Ca–Cu–O tapes

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Abstract
The effect of sintering periods for monocore (Bi, Pb)2Sr2Ca2Cu3O10+x (Bi-2223) tapes on microstructure and critical current density (Jc) have been studied. The results show that long sintering periods (of duration ≥100 h) give better grain growth, but greater misalignment. Prolonged sintering also necessitates the increase in porosity of the core due to random grain growth, increasing the chance of penetrating into the silver matrix and oxide core interface. Critical currents for long sintering periods are found to be lower in comparison with those obtained for slightly shorter sintering periods. The increase in frequency of intermediate cold uniaxial pressing between sintering periods assists grain alignment. However, when the sintering period is further reduced by increasing the frequency of intermediate deformation, it is found that microcracks are unable to heal as there is not enough time for grain regrowth. The tapes made using “three-to-four-sinter-period” (each period ∼60 h) show superior electrical transport properties which are attributable to the fact that their oxide core is more dense and better aligned relative to the “two-sinter-period” (each period ≥100 h) tapes and contain less cracks relative to the “five-to-six-sinter-period” (each period ∼40 h) tapes.