ROLE OF FRACTAL STRUCTURE ON THIN-FILM PROCESSING OF YBa2Cu3O7-x USING ALKOXIDE SOLS

Precursors of the methoxyethoxides of Cu, Y and Ba were synthesised and processed into stable sols with methoxyethanol, methylethyl ketone, toluene and diisopropyl ketone solvents. Pyridine, lutidine and toluene-2,4-disulphonic acid were used to modify the sol behaviour. Small-angle X-ray scattering and small-angle neutron scattering were used to study the structure changes in sols and gels arising from changes in acidity/basicity, moisture exposure and solvent system. Mass-fractal values of 2.0-2.5 were obtained for 0.01-0.1 mol per kg YBa2Cu3 sols in methoxyethanol-methyl ethyl ketone-toluene solvent. Significant effects of pyridine and lutidine on the sol structure were observed as a function of sol concentration. The ability of different solutions to cover SrTiO3, sapphire, SiO2 and silicon substrates was evaluated by contact-angle measurements. Thin films produced by spin casting, dip coating and spray coating were characterised using optical, scanning electron microscopy and X-ray diffraction. The results are discussed in terms of the sol structure. 28 refs.