We report evidence for the reduction of long range lattice order caused by slight departures from the optimal growth temperature in fully doped (x≊0.9) YBa2Cu3O6+xfilms deposited by ion‐beam sputtering on ⟨001⟩ SrTiO3. We estimate the characteristic length of this disorder from the broadening &Dgr;&Vthgr; of the ⟨005⟩ x‐ray diffraction rocking curve. The depression of superconductivity and normal conductivity scales as &Dgr;&Vthgr; and disappears when the in‐plane lattice coherence lengthrc∼1/&Dgr;&Vthgr; is larger than ≊10 nm. ©1995 American Institute of Physics.