Synthesis of YBa₂Cu₃O_7−x fibers from an organic acid solution

A process has been developed for the synthesis of YBa₂Cu₃O_7−x superconducting fibers from an organic acid precursor solution. Through rheology measurements on a series of precursor solutions, the molecular structure was determined and subsequently controlled to allow for fiber drawing. For solutions with a viscosity ⋛10 poise, fibers of 1 to 2 m length and 50 ∼ 100 μm diameter can be hand drawn at ≍80 °C. Processing methods were developed to circumvent deformation of the thermoplastic fibers during heating and to minimize BaCO₃ formation during decomposition. Fibers sintered at 850 °C for 1 h in 10⁻² atm O₂, followed by annealing at 500 °C for 4 h in O₂, were fully dense, consisted of submicron grains, and were superconducting.