OPTIMIZATION OF PRECURSOR FIBER FORMATION CONDITIONS FROM THE Y-BA-CU-CITRIC ACID-H2O SOL

The formation and dissolution of hydroxides, carbonates and citrate complexes, which depend on the pH of the solution, are very important for the preparation of homogeneous and stoichiometric high-T(c) superconducting YBa2Cu3O7-delta-fibers from the Y-Ba-Cu-citric acid-H2O system. Since the solubility of each complex ion is a linear function of pH, the solubility diagram can be obtained by plotting the logarithmic molar concentrations calculated from the values of the equilibrium constants and solubility products for hydroxides, carbonates, and citrates. The optimum pH for preparing homogeneous Y-Ba-Cu-citrate gel fiber is estimated to be 6.0 +/- 0.2. The ceramic fiber (diameter: 0.1-2 mm, length: infinity) obtained after the heat treatment of gel was black colored and the corresponding superconducting transition temperatures (T(c), onset and T(c), offset) have been determined to be approximately 95 and 86 K, respectively.