Effect of fluorine on the superconductivity of YBa2Cu3O7-δ

In order to study the influence of fluorine on the superconducting properties of YBa2Cu3O7-δ in more detail samples of YBa2Cu3FxOy with x = 0, 0.25, 0.50, 0.75, 1.0, 1.25, 1.5, 1.75, 1.8, 1.9, 2.0, 2.1, 2.2, and 2.5 have been prepared. The Ohmic resistance (R) and the diamagnetic susceptibility (χ) as functions of temperature and the onset temperature (T0), zero-resistance temperature (Tc), R120K, and χ77K as functions of the chemical composition are plotted and discussed. Results show that small amounts of fluorine (x ≤ 1) have only a weak influence on the superconductivity of YBa2Cu3FxOy. For x = 2.5 the samples become semiconducting. The compounds with 1.25 ≤ x ≤ 2.5 show new properties. Considering a percolation model of superconducting and non-superconducting crystallites it becomes clear that an increasing part of BaF2 is followed by decreasing χ and decreasing Tc