ROLE OF OXYGEN VACANCIES IN THE FLUX-PINNING MECHANISM, AND HOLE-DOPING LATTICE DISORDER IN HIGH-CURRENT-DENSITY YBA2CU3O7-X FILMS

Critical-current measurements on epitaxial YBa2Cu3O7-x films with 0 less-than-or-equal-to x less-than-or-equal-to 0.2 demonstrate that chain-site oxygen vacancies are not strong flux-pinning centers in high-J(c) films. J(c) decreased steadily with increasing x, consistent with the predicted, monotonic dependence of pinning energy on mobile-charge-carrier density in strongly pinned systems. A correlation between the oxygen pressure p(O2) during high-temperature growth and subsequent response to low-temperature variation of x was observed for T(c). Specifically, films grown at low p(O2) = 0.00026 atm appeared overdoped with holes after oxidation at p(O2) = 1.0 atm, indicative of hole-doping defect formation at low initial oxygen contents.