Chain oxygen disorder in deoxygenated YBa2Cu3O7-delta thin films induced by light ion irradiation

We report on the effects of light ion (He+) irradiation on the superconduct ing properties of epitaxial YBa2Cu3O7-delta thin films. Films were grown by a pure oxygen de sputtering system operated at high pressure (3.4 mbar). I rradiation at 80 keV and doses ranging between 10(14) and 10(15) cm(-2) sho ws a systematic degradation of the superconducting transition temperature. We have studied the effects of annealing on the recovery of the superconduc ting properties of films irradiated at different fluences. Two sets of irra diated samples were evaluated, fully oxidized and deoxygenated samples. Irr adiated fresh samples do not show significant recovery upon room temperatur e annealing for times as long as 6 months. Irradiated deoxygenated samples, however, show an up to 10 K increase in the critical temperature after 2 m onths room temperature annealing. The different behavior is discussed in te rms of the two effects caused by irradiation: oxygen displacements from the CuO chains into stable interstitial positions along the a-axis, and oxygen disorder in the deoxygenated samples. (C) 2001 Elsevier Science B.V. All r ights reserved.