Citrate-derived spin-on films of high T/sub c/ superconductors

Homogeneous liquid citrate precursors have been used to prepare YBa/sub 2/Cu/sub 3/O/sub 7-x/ and Bi/sub 4/Sr/sub 3/Ca/sub 3/Cu/sub 4/O/sub 16+x/ thin films by spin-coating and pyrolysis. Precursor solutions were prepared by dissolution of appropriate metal salts in citric acid and ethylene glycol. Important processing parameters which must be controlled for achieving dense, continuous films include the solution yield, the resin-film thickness, and the time/temperature/atmosphere pyrolysis conditions. In YBa/sub 2/Cu/sub 3/O/sub 7-x/ films, the properties are improved when firing atmosphere and temperature are adjusted to maximize precursor pyrolysis. Typical results are 0.2-0.5 μm films after a single coating, with T/sub c/(onset)=87K and T/sub c/ (R=0)=51K. Critical current densities of 10/sup 4/ A/cm/sup 2/ at 4.2K were measured by direct transport. Results in Bi/sub 4/Sr/sub 3/Ca/sub 3/Cu/sub 4/O/sub 16+x/ films are more promising. Critical current densities of these films, on SrTiO/sub 3/ substrates, were 5 x 10/sup 5/ - 8 x 10/sup 5/ A/cm/sup 2/, with T/sub c/ (onset)--90K and T/sub c/(R=0)=75K. These results are essentially equivalent to those presently obtained by vacuum-deposition processes