Fabrication and characterization of highly pure and homogeneous YBa2Cu3O7 superconductors from sol-gel derived powders

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Abstract
The high Tc superconducting oxide YBa2Cu3O7−d has been fabricated by a simple colloidal sol‐gel precursor technique based on citrate complexes uniformly dispersed into ethyleneglycol and water. The present method permits easier fabrication of highly pure and homogeneous superconducting materials when compared with other more elaborate preparation procedures based on solution techniques as it eliminates many steps such as centrifugation, filtration, and pH control. The purity of the final product was estimated to be >99.5% based on the combined results of x‐ray diffraction and Raman scattering analyses. The composition of the sample was determined to be Y1.00Ba1.98Cu3.05O6.85 by inductively coupled plasma spectroscopy and idiometry. The sol‐gel process produced homogeneous materials with particle sizes smaller than ∼3 μm. The superconducting transition determined with resistivity measurements was shown to be sharp with a transition width narrower than 1 K. The magnetic susceptibility measurements exhibited sharp superconducting transitions without any indication of two‐phase character or impurity phases. The material fabricated by this method showed improved properties compared to those prepared by the usual dry powder‐mix (so‐called solid‐state reaction) technique.