High T C Superconductor Fibers from Metallo-Organic Precursors
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HIGH Tc SUPERCONDUCTOR FIBERS FROM METALLO-ORGANIC PRECURSORS K.C. CHEN AND K.S. MAZDIYASNI General Atomics, PO Box 85608, San Diego, CA 92138-5608 ABSTRACT Homogeneous solution for Y-Ba-Cu-O superconductor was prepared from The yttrium i-propoxide, barium i-propoxide, and copper ethylhexanoate.
solution was converted to a resin-like material and was readily dissolved in organic solvents. The resin possesses a cohesive property in a number of solvents, such as benzene and xylene. Single-phase superconducting YBa2Cu 3O7 _x fibers have been continuously spun from the viscous solution. Controlled amounts of Y2 BaCuO5 phase in the fibers were made possible by Partial substitution of slight adjustments in the solution compositions. copper ethylhexanoate with copper trifluoroacetate prevents barium carbonate formation in the fiber during curing and organic pyrolysis. INTRODUCTION For the new high Tc superconducting ceramics to be useful, they must be made into desirable shapes. Specifically, the magnetic applications critically depend on the fabrication of fibers or tapes that carry sufficiently Fabrication of YBa2Cu3O7_x superconductor ceramic high electrical current. fibers or wire with adequate strength, modulus, and electromagnetic properties is a formidable task because the yttrium barium cuprate ceramic material is brittle and is not easily drawn into the desirable fine fiber geometry. Such fiber property requirements demand high chemical and phase purities as well as crystallographic orientation in the a or b direction, uniform microstructure, and clean grain boundaries. Various methods have been used to prepare superconducting fibers (1]. The powder-in-binder (2], powder-in-sol (3], sol-gel and metallo-organic [4-8] methods adopt the spinning process, which has been established for ceramic fiber-making. In this paper, we discuss the method involving the preparation of single phase YBa 2 Cu3 07_x fibers and fibers with minor Y2 BaCuO5 phase inclusions from metallo-organic precursors. We also describe modification of the solution chemistry to overcome barium carbonate formation. EXPERIMENTAL PROCEDURES Yttrium i-propoxide/i-propanol solution was prepared by the method described by Mazdiyasni, et al. [9]. Barium i-propoxide/i-propanol solution was prepared by reacting barium metal chips (Alfa Products) with dry i-propanol. Copper ethylhexanoate/i-propanol solution was made by dissolving copper ethylhexanoate (Alfa Product) in dry i-propanol. Copper trifluoroacetate was synthesized by reacting copper ethoxide (Alfa Products) with trifluoroacetic acid. Stoichiometric (YBa 2 Cu3O7 _x) or off-stoichiometric (YBa 2 Cu3O7_x + y Y2 BaCuO5 )• solutions were obtained by pipetting the calculated volumes from each stock solution. In cases where copper trifluoroacetate were used, 2/3 to I mole of copper trifluoroacetate per mole of yttrium was added to partially substitute for copper ethylhexanoate. A green precipitate formed when copper solution was introduced. This precipitate was hydrolyzed by adding water/isopropanol solut
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