Synthesis of superconducting thin films by organometallic decomposition

Processing of superconducting thin films has been attempted by three chemical routes. Only one of these routes was successful; this process consisted in the deposition and theraml decomposition of a solution of yttrium, barium and copper 2 ethyl hexanoates dissolved in chloroform. By careful drying and pyrolysis, smooth crack-free films with a thickness of 1-2 μm were obtained. After appropriate firing, films are synthesized on MgO with a superconductive transition starting at 90 K and ending at 72 K (Tc, R<10-3 Ω). This low Tc value could result from an imbalance stoichiometry in the precursor solutions which promotes the formation of insulating impurity phases. These films have a highly oriented crystallographic structure which results in high critical current value (Jc=13000 A/cm2). Films have been also synthesized on polycrystalline alumina with a superconducting transition from 60 K to 29 K. This decrease in the transition temperature is a result of the diffusion of aluminium into the film. From this study, the stoichiometry of the precursors, temperature of firing, and time of firing, appear to be the predominant processing parameters. A careful study of their relative importance on the final characteristics of the films is needed to produce films with characteristic approaching those of physical deposition. (orig.)