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

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.

Effects of the reaction time on various properties of tapes

“…In summary, both SEM and XRD measurements clearly indicate that 40 h after the first annealing the Bi(2223) platelets are already present in their final morphology and orientation and that no decomposition of the Bi(2223) occurs up to 240 h. In addition, we found no evidence of an increase in the ceramic core porosity, as reported by some authors (e.g. [23]).…”

Effects of precursor powder calcination on critical current density and microstructure of Bi-2223/Ag tapes

“…Considerable progress has been made in fabricating (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x (Bi-2223) tapes or wires with high critical current densities that are attractive for electric power and high-field magnet applications [1][2][3][4][5][6][7][8][9]. The transport critical current density of the Bi-2223 tapes has been found to depend significantly on heat treatment temperature [4], precursor powder [6,9,10], sintering time [11] and mechanical deformation [9,12]. Although some parameters are believed to be optimized, it should be emphasized that a better control of the variables, for example, the precursor powder, is still needed in order to increase the reproducibility of the transport properties in long tapes.…”

Reactive Sintering and Retrograde Densification of Bulk Bismuth‐Based Superconductors

“…3), which agrees with earlier reports. 19 We found that grains grow in the a/b plane from a size of ϳ15 m at 0.3 h to ϳ80 m at 50 h, whereas grain growth in the c-direction is negligible. Although the amount of liquid probably is insufficient for particle rearrangement beyond 4 h, the residual liquid could be sufficient to enhance grain growth.…”