Precursors physico-chemical properties and influenceon the morphology and stoichiometry of films depositedby spray pyrolysis for YBCO synthesis

摘要

YBCO thick films with high Jc over 1.4 MA/cm2 (77K, selffield) have been synthesized using the nitrate spray pyrolysis process onSrTiO3 (001). Despite its high efficiency, the mechanisms of depositionand growth involved in spray pyrolysis are quite unknown. This workaims to examine the precursors physico-chemical properties and theirinfluences on the morphology and the composition of the films. Nitratesdecomposition mechanisms have been investigated by thermogravimetricand differential-thermal analysis (TG/DTA) and X-ray diffraction (XRD).Spray pyrolysis experiments have been performed on individualprecursors and compared to these combining two mixed precursors. Thepresence of an element melting on the substrate is an essential ingredientfor the growth of a film, its morphology and its texture. Conversely thefoam morphology observed for the yttrium phase makes impossibleyttrium oxide film formation. It is proved that only a mix with bariumnitrate enables yttrium-based film formation. Experiments at differenttemperatures made for mixtures of Y, Ba and Cu show that thestoichiometric ratio for Y and Ba is preserved during depositionconversely to that for Y and Cu or Ba and Cu. This suggests that thecopper oxide is deposited according to a different mechanism than thoseof Y and Ba oxides.