Yulia Lumelsky

Polymers that form a complex with metal ions from nitrate salts can be used to prepare castable precursors for the production of high temperature superconductor (HTSC) ceramics. An HTSC precursor using a UV-sensitive polymer can be patterned using microlithography to form structures such as microbridges and then pyrolyzed to HTSC. The objectives of this research were to study degradation and HTSC formation in HTSC precursors containing an m-cresol formaldehyde resin (Novolak). Films containing Novolak and different percentages of metal nitrates were cast from solution. Yttrium, barium and copper nitrates with Y:Ba:Cu ratios of 1:2:3 were used to produce  (YBCO) on pyrolysis. The formation of complexes between Novolak and the metal nitrates was studied using Fourier transform infrared spectroscopy (FTIR). The degradation was characterized using differential scanning calorimetry and thermogravimetric analysis combined with FTIR. The formation of YBCO was characterized by X-ray scattering, high-resolution scanning electron microscopy and energy dispersive spectroscopy. The different phases and the orientation of the YBCO films were studied by means of electron backscatter diffraction. The addition of metal nitrates reduced the glass transition temperature and the thermal stability and altered the mechanism of polymer degradation. The formation of YBa₂Cu₃O_7-x and the amount of additional phases present were found to be affected by the physical form of the HTSC precursor, the pyrolysis process, the nature of the substrate and the nature of the polymer. Pyrolysis that began in an inert atmosphere and continued in pure oxygen at high temperatures enhanced the formation of HTSC by limiting the formation of additional phases and eliminating carbonaceous residues. A highly oriented YBCO film on a SrTiO₃ substrate could thus be produced through pyrolysis of a Novolak precursor at 950ºC for 3h, as opposed to the standard solid­state process that involves tens of hours at 1050ºC.