PHASE AND TEXTURE FORMATION IN BI-2212 AG TAPES PROCESSED IN OXYGEN/

Bi-2212 phase formation was studied in silver-clad tapes processed by melt-texturing in an oxygen atmosphere. Stoichiometric Bi-2212 was fou nd to undergo a peritectic decomposition, which starts at 883 degrees C (+/-2 degrees C), into a Bi-rich liquid and two alkaline-earth cupra te solid phases: (Sr, Ca)(14)Cu24Ox and Bi(Sr, Ca)(2)O-x. This phase a ssemblage remained unchanged up to 910 degrees C, where the solid phas e crystals were found to have a random orientation. Some Ag was found to dissolve into the liquid, and concentrate around the 14:24 crystals . On cooling, at 874 degrees C, the Bi-2212 crystals randomly nucleate d from the liquid. At 869 degrees C, the Bi-2212 crystallite size was in the range of 0.1 to 0.4 mu m. The phase assemblage consisted of Bi- 2212 as the major phase, and Cu-free and trace 14:24 crystals as the m inor phases. The 14:24 crystals were highly oriented relative to the s ilver interface. As the minor phases diminished, the texture of Bi-221 2 crystals, having the c axes perpendicular to the silver-core interfa ce, improved. These observations suggest that Bi-2212 crystals nucleat e from the liquid on the surface of the 14:24 phase as well as at the silver-core interface, and the dissolved silver in the liquid may play an important role.