FLUORINATION OF Y1BA2CU3O7-X BY A SOLID-STATE ELECTROCHEMICAL METHOD

A solid state electrochemical method has been employed to fluorinate Y1Ba2Cu3O7-x pellets of stoichiometry close to Y1Ba2Cu3O6.2 and Y1Ba2Cu3O6.9. The optimum condition for the coulometric titration of fluorine was found to be at a temperature of less than 673 K and for titration into tetragonal material of low oxygen stoichiometry. The lattice parameter trends upon fluorination of both the reduced and oxidised samples indicate that fluorine atoms occupy O(1) and O(5) sites in the basal plane of the lattice and that some fluorine/oxygen exchange takes place at the O(1) sites. In addition, a tetragonal lattice configuration is approached at high fluorination levels, regardless of the initial oxygen stoichiometry of the samples before fluorination, and the phase is more thermodynamically stable than the pure oxide. The superconducting properties of the fluorinated material were not enhanced above the maximum value of 92 K measured in the pure oxide phase. However, T(c) onsets as high as 87 K were measured in samples of the Y1Ba2Cu3O7-xFy phase of initial oxygen stoichiometry close to '7-x' = 6.9, and as high as 60 K in Y1Ba2Cu3O7-xFy samples of the initial oxygen stoichiometry, '7-x', close to 6.2.