Superconducting Fibers from Anhydrous Metal Carboxylates
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SUPERCONDUCTING FIBERS FROM ANHYDROUS METAL CARBOXYLATES RICHARD M. LAINE,* KAY A. YOUNGDAHL, RICHARD A. KENNISH, MARTIN L. HOPPE, ZHI-FAN ZHANG and D. JEAN RAY, Contribution from the Polymeric Materials Laboratory of the Washington Technology Center and the Dept of Materials Science and Engineering, University of Washington, Seattle, WA 98195 ABSTRACT: A variety of anhydrous Y, Ba and Cu carboxylates were synthesized and screened for utility as spinnable precursors to 123 superconducting fibers. Simple extrusion studies demonstrate that THF solutions of mixtures of Y, Ba and Cu isobutyrates with some Ba 2-ethyl- hexanoate can be used to form 70 pinm dia. precursor fibers. Following a curing at 150°C for 24-48 h, pyrolysis of these fibers in air to 900*C, with controlled heating rates, gives dense, flexible ceramic fibers 15-20 gtm in dia. These fibers have the appropriate orthorhombic phase. Flux exclusion measurements indicate the fibers are superconducting; but ATe is not optimal. INTRODUCTION The rush to develop practical applications for the new, high Tc superconducting ceramic oxides has led to tremendous advances in thin film processing with respect to reproducibility, phase purity and high Jc.1. 2 By comparison, bulk materials lag far behind. There are many 3 reasons for this, but the need to develop high Jc bulk materials is the primary obstacle. In principle, the development of superconducting fibers or wires should offer a transition between thin films and bulk because the dimensions required to obtain flexibility and mechanical strength in ceramic fibers are within an order of magnitude of the dimensions of the thin films. Unfortunately, there are no generally accepted or straightforward methods for the fabrication of thin, oxide ceramic fibers of any type. Consequently, progress in this realm is relatively slow by 4 comparison with the processing technologies being developed for thin film applications. -9 One major objective of our research program is to develop standard processing methodology for the design, synthesis and processing of organometallic preceramic polymers into oxide and non-oxide ceramic fibers. In this paper, we present an overview of our recent efforts to develop anhydrous metal carboxylate precursors to the YBa 2 Cu 307.x, 123 superconducting oxide 1 12 ceramic. More detailed studies will be presented in a series of papers published elsewhere. °RESULTS AND DISCUSSION We have examined the utility of metal carboxylates as precursors to 123 fibers because they
Mat. Res. Soc. Symp. Proc. Vol. 180. @1990 Materials Research Society
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offer several advantages over sol-gel processing approaches. In particular, their rheological properties are controlled by electrostatic and mechanical crosslinking interactions rather than hydrolytically induced crosslinking. These same crosslinking mechanisms permit effective atomic mixing of the metal components in the precursors polymers. In contrast, atomic mixing in sol-gel processing, especially of multicomponent oxides, is often difficult to obta
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