MICROSTRUCTURE OF THE MELT-TEXTURED BI1.6PB0.4SR2CA2CU3O10 SUPERCONDUCTOR USING SRO AS SUBSTRATE

We have discovered that SrO is a good ''intervening substrate'', in a melt-textured-growth (MTG) process, to be placed between the bulk sample and crucible to minimize loss of sample mass due to diffusion. The fractured surfaces of the subsequent MTG bulk sample show highly oriented layers a few mu m thick in regions on a scale of approximate to 100 mu m Some of the layers were found to be composed of further thinner parallel layers of approximate to 0.2 mu m Transmission electron microscopy observation reveals that fringes representing the c axis of the aligned 2223 crystals appear in many of our film samples of thickness approximate to 70-80 nm. Tangles of dislocations, tweed structure and crosshatched lattice fringes; were discovered. Although a very slow cooling rate of 0.5 degrees C h(-1) was used during the crystal formation period, lattice fringes of various directions and structures show up on 100 nm-100 Angstrom scales. The difference between the microstructure of the Bi specimen and that of the Y-class samples is discussed.