In this work, the reaction mechanism used in the preparation of fluorine-free superconducting YBa(2)Cu(3)O(7-delta) (YBCO) was investigated. To determine which precursor interactions are dominant, a comprehensive thermal analysis (thermogravimetric analysis-differential thermal analysis) study was performed. The results suggest that a three step reaction mechanism, with a predominant role for BaCO(3), is responsible for the conversion of the initial state to the superconducting phase. In the presence of CuO, the decarboxylation of BaCO(3) is kinetically favored with the formation of BaCuO(2) as a result. BaCuO(2) reacts with the remaining CuO to form a liquid which ultimately reacts with Y(2)O(3) in a last step to form YBCO. High temperature X-ray diffraction experiments confirm that these results are applicable for thin film synthesis prepared from an aqueous fluorine-free sol-gel precursor.
In this work a fluorine-free sol–gel method based on low-cost materials and water as
primary solvent is developed, resulting in a sustainable superconducting film. Using a 0.6 M
‘AWAT’ precursor (M-acetates, water, acetic acid and tri-ethanolamine, patent pending)
YBa2Cu3O7−δ (YBCO) films
were dip coated on SrTiO3
(STO) single-crystal substrates. After gelation at
60 °C, the
amorphous gel was transformed to the desired crystalline superconducting phase. Sintering was conducted
at 815 °C
under a 200 ppm oxygen partial pressure, followed by a pure oxygen annealing at
400 °C. Highly
textured (Δω = 0.2°,
Δφ = 6.5°) YBCO
films with a Tc,onset
of 92 K, a ΔTc
of 5 K, a Jc
of 0.55 MA cm−2
and an Ic
of 25 A cm−1
width at 77.3 K and self-field were achieved. Experimental results on film synthesis,
morphology, microstructure and superconducting properties are presented.
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