MICROSTRUCTURAL EVOLUTION THROUGH A THERMAL-TREATMENT TO OBTAIN NEEDLE-SHAPED GRAINS OF BI2SR2CACU2O8+X

In a previous paper, we presented a novel grain structure for Bi(2212) , which consists of needle-shaped grains of around 1 mm length and 100 mu m diameter (Cabeza, O., Avecilla, F., Barca, O. and Miguelez, F., Bol. Sec. Esp. Ceram. Vidrio, 1995, 34, 436 (in Spanish); also submitt ed to J. Mater. Sci.). In this paper, we present an improved thermal t reatment to obtain this new structure. We study the structural changes suffered by the conventional ceramic Bi(2212) sample through that the rmal treatment using scanning electron microscopy. We have performed m agnetization measurements in the samples to observe their superconduct ing nature. Both the shape and the size of these grains seem to be ver y suitable for making superconducting tapes, mainly because the number of grain boundaries would be drastically reduced. (C) 1997 Published by Elsevier Science Ltd.