Critical current density dependence of bulk textured Bi-2223 on thermal treatments and cold intermediate pressing

摘要

We report bulk Bi-2223 transport measurements for samples of various synthesis conditions. The measurements were carried out at 77 K in self-field and the critical current density, J_C, reaches up to 12000 A/cm~2 depending on the sample's preparation. The samples were prepared using a polymer matrix method. The same calcination procedure was performed on all the samples. After milling and pelletizing, calcined pellets were either directly sinter-forged (838°C/20 h/10 Mpa) or sintered at 838°C for various times (25-50-75-100-150-200 h) before being sinter-forged under the same conditions as the just-calcined pellets. The resulting hot-forged discs were analysed in terms of texture quality (50% of the Bi-2223 grains are aligned within an angle ranging from 6.2°to 3.9°) and Bi-2223 phase percentage (ranging from 26% to 95%). The discs were cut into bars which were either directly annealed (825°C/100 h + 1°C per hour to 800°C under 7.5% O_2 balance N_2) or subjected to various (1-3) sintering steps (838°C/50 h) with or without intermediate cold pressing (1 GPa) before annealing. Transport measurements were performed on these samples, and the results are discussed in terms of Bi-2223 phase percentage, texture quality, grain boundaries, effect of cold intermediate pressing and post sintering. This novel type of bulk synthesis process is similar to the one used for tapes, and it allows the preparation of more reproducible bulk samples with high J_C values and better grain connectivity.