THE MICROSTRUCTURE OF SOLUTION-SPUN Y0.75HO0.25BA2CU3OX FILAMENTS GROWN ON MGO SUBSTRATE

Y0.75Ho0.25Ba2CU3Ox filament with a diameter of 250 mu m was prepared by dry spinning through a starting homogeneous PVA aqueous solution of Y, Ho, Ba and Cu acetates. The as-drawn filament was pyrolysed to rem ove volatile components and annealed on various substrates under a two -step method of O-2 partial pressure in Ar and pure O-2 ROW. A filamen t pyrolysed at 400 degrees C at a heating rate of 30 degrees C h(-1) a nd annealed at more than 840 degrees C for 15 h on single-crystal (100 ) MgO was solid, in spite of the other filament being hollow. Preferre d orientation of the 123 crystalline was not observed. The maximum J(c ) of 3900 A cm(-2) at 77 K and 0 T was attained for a filament grown a t 880 degrees C on polycrystalline MgO. The J(c) and microstructure of the filament are strongly dependent on the pyrolysis temperatures.