Metal-Organic Precursors to high Temperature Superconductors Using 2-(2-Ethoxyethoxy)Ethanol
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METAL-ORGANIC PRECURSORS TO HIGH TEMPERATURE SUPERCONDUCTORS USING 2-(2-ETHOXYETHOXY)ETHANOL MARY ROSE SCOZZAFAVA, WENDELL E. RHINE, AND MICHAEL J. CIMA Ceramics Processing Research Laboratories, Massachusetts Institute of Technology, Cambridge, MA 02139 ABSTRACT The copper(II) alkoxide, bis(2-(2-ethoxyethoxy)ethoxide)copper(II), was prepared and had a solubility in organic solvents greatly exceeding those of simple copper(H) alkoxides (>0.4 mol/L in toluene at room temperature). Copper 2-(2-ethoxyethoxy)ethoxide (2-(2ethoxyethoxy)ethoxide = 2,2-EEE) toluene or toluenefTHF solutions gelled upon exposure to moisture. These solutions were hydrolysed with 0.2, 1.0, 2.0, 4.0, and 20.0 equivalents of H20 and the resulting powders were characterized by IR spectroscopy and SEM. INTRODUCTION The production of high quality Ba 2 YCu 306.9 films by chemical routes is important for commercial applications of high temperature superconductor technology. Solution methods of preparing high temperature superconducting oxides are appealing because of the possibility of using lower processing temperatures due to the intimate mixture of precursor materials and the capability of coating complex surfaces, such as the interior surface of RF wave guides. Metal alkoxides offer an additional advantage over other metal-organic systems, in that, hydrolysis of the precursor solution yields a metal hydroxide and free alcohol. The alcohol can be removed by vaporization which lowers the carbon content of the precursor solution. The reduced carbon content minimizes or prevents BaCO 3 contamination in the resulting film. However, the insolubility of copper(ll) alkoxides has limited the success of this route. Increased understanding of the solubilities and the hydrolysis and condensation reactions of copper alkoxides are necessary to the design of solution processes for high temperature superconductors. We describe the preparation, solubility and hydrolysis of a highly soluble copper(II) alkoxide, bis(2-(2-ethoxyethoxy)ethoxide)copper(II) (bis(2-(2ethoxyethoxy)ethoxide) = 2,2-EEE). EXPERIMENTAL All reactions were conducted under inert atmosphere using dried solvents. Cu(2,2EEE) 2 was prepared by an alkoxide exchange reaction in toluene between Cu(OMe) 2 and 2(2-ethoxyethoxy)ethanol. The resulting clear blue solution was filtered and the copper concentration was determined by iodimetric titration. Cu(2,2-EEE) 2 was isolated as a solid by toluene evaporation of the solution under reduced pressure, followed by heating under vacuum to remove unreacted 2-(2-ethoxyethoxy)ethanol. Copper 2-(2-ethoxyethoxy)ethoxide solutions (0.029 moI/L) in 2:1 toluene:THF were hydrolysed by the addition of 0.2, 1.0, 2.0, 4.0, or 20.0 equivalents of DI H20. Exposure of the solutions to atmospheric moisture was avoided by using inert atmosphere techniques. Hydrolysis resulted in homogeneous solutions, suspensions or precipitates. The solutions were characterized by solution cell FTIR spectroscopy. The solids were characterized by DRIFTS (Diffuse Reflectance Infrared Fourier
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