Synthesis of Superconducting Thin Films by Organometallic Decomposition
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SYNTHESIS OF SUPERCONDUCTING THIN FILMS BY ORGANOMETALLIC DECOMPOSITION
CHRISTOPHE BARBE AND TERRY A. RING Powder Technology Laboratory, Swiss Federal Institute of Technology, CH- 1015 Lausanne, Switzerland 1) INTRODUCTION The discovery of high critical temperature superconducting oxides 1,2 has stimulated intensive research activities aimed not only at understanding the physical mechanisms of superconductivity, but also developing techniques to produce these ceramics in useful forms. A promising application for superconductors is in electronic components industry which has given rise to an interest in the various ways of producing thin films of superconducting materials. Physical depositions techniques have been successful in producing films with the desired physical characteristics (i.e. high Tc and Jc), but these processes are expensive and do not allow any versatility in the substrate geometry. Chemical deposition techniques such as the spray, dip, and spin coating of a solution onto a substrate, are attractive because they avoid these problems. This is why we have focused our attention on the deposition of solutions by these techniques to produce the superconducting thin films of YBa2Cu3O7-x. also known as the 1:2:3 phase. Out of the many chemical routes for producing superconducting thin films 3-8, the process that we have found to show the most promise is the dipping-pyrolysis procedure for a carboxilate solution of yttrium, barium and copper in chloroform. The solution chemistry, drying, pyrolysis, and high temperature treatment of the film will be discussed in detail. 2) EXPERIMENTAL PROCEDURE Various organic salts 9-14, differing by the carbon chain length, have been used to prepare solutions for a dip (or spin) and pyrolysis process. The following precursors were used in our experiments: 1) copper 2-ethyl hexanoate, 2) barium 2-ethyl hexanoate, and 3) either yttrium naphtenate or yttrium 2-ethyl hexanoate. These three compounds are mixed in the desired 1:2:3 stoichiometric ratio in chloroform to make homogeneous viscous solution. In reality this 1:2:3 stoichiometric ratio was not achieved exactly. The elemental analysis of the precursors showed an inaccurate assay (as provide by the supplier) which had lead us to a 1:2:3.1 in the (Y+Ba+Cu) 2-Ethyl hexanoates solutions. The solutions were then slowly deposited on an appropriate substrate by dipcoating. Because of the low surface tension of those solutions, any number of ceramic substrates can be used. The rheological properties of these solutions were studied in order to control film thickness during the dipcoating procedure. Thermal analysis of the different solutions was used to define the parameter of the heat treatment specifically. The results of this analysis suggested the steps for the heat treatment. The final films were then analyzed by X-ray diffraction, EDX, SEM and four point resistivity measurements. The results are presented below.
Mat. Res. Soc. Symp. Proc. Vol. 180. 01990 Materials Research Society
884
3) RESULTS AND DISCUSSION 3.1 So
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