Structure evolution during thermal processing of high-Tcceramic superconductors produced using sol–gel techniques

Abstract

Characterization of the decomposition and phase development reactions for CuII methoxyethoxide, 2Ba–3Cu, Y–3Cu, and Y–2Ba–3Cu gels has been performed using in situ neutron diffraction and differential thermal analysis (DTA). The structual 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 °C, and that a firing temperature of 850 °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 °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.