STRUCTURE EVOLUTION DURING THERMAL-PROCESSING OF HIGH-TC CERAMIC SUPERCONDUCTORS PRODUCED USING SOL-GEL TECHNIQUES

Characterization of the decomposition and phase development reactions for Cu(II) methoxyethoxide, 2Ba-3Cu, Y-3Cu, and Y-2Ba-3Cu gels has been performed using in situ neutron diffraction and differential thermal analysis (DTA). The structural evolution process of a Y-2Ba-3Cu gel to the superconducting YBa2Cu3O7-x phase was elucidated using the acquired spectra. Precursor gel powder was produced from an alkoxide sol-gel system having a methoxyethanol, methyl ethyl ketone and toluene solvent mixture. Neutron diffraction results indicate initial YBa2Cu3O7-x formation below 700-degrees-C, and that a firing temperature of 850-degrees-C is sufficient to produce essentially single-phase YBa2Cu3O7-x. The conversion of BaCO3 to BaCO3 polymorph was observed to occur between 790 and 800-degrees-C, after which rapid formation of the YBa2Cu3O7-x tetragonal phase occurred. The results also indicate an incomplete conversion of the non-superconducting tetragonal phase to the superconducting orthorhombic phase during the cool-down and annealing segments of the heat treatment.