Role of oxygen vacancies in the flux-pinning mechanism, and hole-doping lattice disorder in high-current-density ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ films

Critical-current measurements on epitaxial ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ films with 0≤x≤0.2 demonstrate that chain-site oxygen vacancies are not strong flux-pinning centers in high-${\mathit{J}}_{\mathit{c}}$ films. ${\mathit{J}}_{\mathit{c}}$ decreased steadily with increaing 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 ${\mathit{p}}_{\mathrm{O}2\mathrm{}}$ during high-temperature growth and subsequent response to low-temperature variation of x was observed for ${\mathit{T}}_{\mathit{c}}$. Specifically, films grown at low ${\mathit{p}}_{\mathrm{O}2\mathrm{}}$=0.000 26 atm appeared overdoped with holes after oxidation at ${\mathit{p}}_{\mathrm{O}2\mathrm{}}$=1.0 atm, indicative of hole-doping defect formation at low initial oxygen contents.