Chemical vapour deposition processes (CVD) can produce metastable fine-grained materials as well as epitaxial coatings and can have a very large throwing power depending on the process parameters. Therefore, CVD is an prospective method to deposit high-temperature superconducting materials with T c >~ 10 K. One of the first superconductors which were produced was Nb3Sn on tapes and single wires. This superconducting material is, however, today produced by metallurgical methods. Since the detection of Nb3Ge, CVD has become for these coatings the main method of production for the following reasons: high deposition rates, possibility to dope the material by addition of further doping gases to the CVD-process, continuous process. These coatings were deposited on tapes. For the first time the large throwing power of the CVD process was utilized for the deposition of B1-NbCxN v on carbon fibre bundles. This opens the possibility to produce multifilamentary structures used for magnetic applications. The structure of the coating can be varied by changing the gas properties, by addition of further gases, by an ultrasonic field, by ignition of a gas discharge and by multi-layering. CVD could also be a prospective method for producing the new class of superconductors with T c >~ 30K.
Le dgp8t chimique en phase vapeur est une m&thode prometteuse pour produire des supraconducteurs ,81haute temp6rature. En effet cette technique permet le depot sous haut potentiel d90xyg&ne avec des vitesses Qlevees par rapport & celles obtenues pour les autres methodes de dQp8t. Sa potentialitb est grande et on peut revatir des substrats de g60m6trie complexe (ex: fibres). Les B-didtone chelates de Y, Ba, Cu ont &t6 utilises commme precurseurs pour le depat,, 2e YBa2Cu307-6. Pour definir le procede de depot. llhydrodynamique du reacteur a 6t6 determinee par des simulations et des expgriences (fumees de Ti02). L& dgp8ts effectu6s sur monocristal de SrTi03, et-sur des substrats polycristallins de zircone stabilisee a l'yttrium, sont supraconducteurs au-dessus de 94 K et ayant dans le cas des substrats S ~T ~O ~ une densit& de courant de 105 A pour un champ magn&tique disponible maximal de B = 5.5 Tesla, 3 77 K.
The evaporation behaviour of Ba(thd)2 in a CVD-process for HTc-Superconductors is presented. The long-time stability as well as possibilities to increase the evaporation rates by changing the geometry of the evaporator and the process conditions are discussed.
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