SOL-GEL PROCESSING OF CERAMIC SUPERCONDUCTORS

High Tc superconducting powders and thin films have been developed through sol-gel processing. Powder and film preparation involved the synthesis of metal alkoxides (Cu(II)-ethoxide, Ba-methoxyethoxide, and Y-methoxyethoxide) followed by the complexation of the alkoxides in common solvents. A polydisperse colloidal suspension of yttrium, barium, and copper alkoxides, which was characterized by light scattering, was obtained during hydrolysis and complexation reactions. This technique revealed a particle size reduction by a factor of 5 (1100 nm to 200 nm) within a 24 h time period. The water/alkoxide ratio was varied between 1:1 and 4:1 (mole ratio) which resulted in a sol-gel transition time of two to five days and a Tc of 83 to 78 K, respectively. The metal alkoxide chemistry was also used to produce highly oriented superconducting thin films on SrTiO3 substrates. Although scanning electron microscopy revealed that the film consisted of oriented polycrystallites, from the broad statistical X-ray diffraction data, they appeared to have a moderate mosaic spread (i.e. full width at half-maximum was 0.3° in θ at a 2θ of 55°). No twinning of the crystallites was found in any of the three orthogonal directions (θ, φ, χ). The onset temperature Tc for the film was 55 K while the critical current density Jc was found to be 100 A/cm2. © 1990.