The degradation of novolak containing metal nitrates and the formation of YBCO

Polymers that form a complex with metal ions from nitrate salts can be used to prepare precursors for the production of high temperature superconductor (HTSC) ceramics that can be processed using advantageous polymer processing techniques and then pyrolyzed. This paper describes the production of HTSC from a precursor based on m-cresol formaldehyde novolak resin (mCFNR) that contains yttrium, barium and copper nitrate salts in the proportions needed for the formation of YBa2Cu3O7–x (YBCO). The degradation of the precursor and the effects of the pyrolysis process (temperature, time, environment, substrate) were studied in detail. The mechanisms of degradation for mCFNR and for the HTSC precursors were significantly different with the precursor degradation beginning at significantly lower temperatures. The optimal pyrolysis begins in an inert atmosphere to hinder BaCO3 formation and then continues in oxygen to 950 C. A dense orthorhombic YBCO film with preferential [001] orientation results from topotaxial growth on SrTiO3.