Preparation Of Copper And Copper-Barium-Yttrium Sols From Metal 2-(2-Ethoxyethoxy)Ethoxides and Conversion Of Copper-Bar
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PREPARATION OF COPPER AND COPPER-BARIUM-YTTRIUM SOLS FROM METAL 2-(2-ETHOXYETHOXY)ETHOXIDES AND CONVERSION OF COPPER-BARIUM-YTTRIUM ALKOXIDE PRECURSORS TO Ba 2 YCu 3O7 -6. Mary Rose Scozzafava, Wendell E. Rhine, and Michael J. Cima Ceramics Processing Research Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139
ABSTRACT The hydrolysis of copper 2-(2-ethoxyethoxy)ethoxide solutions and barium-yttriumcopper 2-(2-ethoxyethoxy)ethoxide solutions were investigated. Copper sols with particle sizes of 3-10 nm have been prepared from THF solutions. Sols from barium-yttrium-copper alkoxides were also prepared in THF with particle sizes of 4-10 nm as determined by transmission electron microscopy (TEM) and 50-80 nm as determined by photon correlation. Compositional analysis showed that the sols had a similar composition to the parent solution. Choice of atmosphere and solvent system played an important role in the progress of the hydrolysis reaction. Powders obtained from barium-yttrium-copper solutions can be converted to Ba 2 YCu 3O_8. INTRODUCTION Sol-gel synthesis has been studied intensively as a fabrication method for superconducting films and powders [1-7]. The process involves dissolution of barium, yttrium, and copper alkoxides in a common solvent followed by addition of water which initiates hydrolysis and condensation reactions which can produce either a sol or gel. The resulting solutions can then be spin- or dip-coated onto substrates or dried to obtain powders which, upon heat treatment, yield high T, superconducting oxides. The insolubility of Cu(lI) alkoxides, however, has limited the success of this route. Recent improvements in preparing soluble copper alkoxides involved the use of polydentate ligands in which the second heteroatom can help satisfy the coordination sphere of copper and increase its solubility [3-7]. The preparation of bis(2-(2-ethoxyethoxy)ethoxide)copper(Il), Cu(OCH 2CH 2OCH 2CH2OCH 2CH 3) 2 , is part of an ongoing effort to develop soluble copper alkoxide precursors to apply sol-gel technology to the preparation of superconducting oxide films and powders [3]. Preliminary investigations showed that copper 2-(2-ethoxyethoxy)ethoxide [2-(2-ethoxyethoxy)ethoxide = 2,2-EEE)] is a good candidate for use in sol-gel procedures [3]. Cu(2,2-EEE) 2 is highly soluble in both THF and toluene. Further motivation for the study of soluble copper alkoxides is that copper sols could be used as a route to extremely fine copper particles. Metal precipitates are used in glass coatings to change their optical properties. Typically, the particles are introduced by fuming salts of the metal onto the glass surface. Copper sols instead could be spin-coated with a silica sol and then fired under a reducing atmosphere to give monodispersed copper metal [8]. In this paper, we report on the hydrolysis behavior of Cu(2,2-EEE) 2 and of mixtures of copper, barium, and yttrium 2-(2-ethoxyethoxy)ethoxides. Conditions for formation of stable sols of both copper and barium-yttrium-copper are described. Po
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