MICROSTRUCTURE DEVELOPMENT IN REPEATED ZONE-REFINING OF MICROWAVE-DERIVED YBCO BULK COMPACTS

YBCO precursor particulates have been prepared using microwave decomposition of a mixture of yttrium, barium and copper nitrates in a microwave oven having the frequency 2.45 GHz and 600 W power, within as short as 240 seconds. This precursor, upon further compaction into strips of 10 mm x 60 mm x 1 mm and sintering at 940-degrees-C for 5 h, attained 90% density. Such strips are subjected to repeated zone refining operations in a zone refining system having a three-zone furnace at relatively high speeds of 30 mm/h. The development of microstructure in such samples from the as-sintered condition through the various steps has been presented. A microstructure having uniformly oriented grains in the a-b plane throughout the bulk of the sample could be obtained by three repeated zone refining operations. The possibility of introducing a faster movement of the melting zone compared to earlier reports, is highlighted.