Effects of irradiation induced lattice disorder in superconducting YBa2Cu3O7 films

A report is presented on the preparation of thin films of the high-T_c superconductor YBa₂Cu₃O₇ by DC-magnetron sputtering and the effects of structural disorder introduced by irradiation with 25 MeV ¹⁶O-ions on superconductivity and normal state electrical resistivity. By suitable heat treatments polycrystalline films of different quality could be prepared on SrTiO₃ and Al₂ O₃ substrates. The upper critical field B_c2( T) of high-T_c films measured up to 6 T is linear with dB_c2/dT=-2 T/K. Irradiation with 25 Me oxygen ions leads to a linear reduction of T_c and an increase of ρ(100 K) with fluence. The sensitivity of T_c to irradiation depends significantly on the quality of the films. For high-T_c films B _c2(T) remains linear with increasing slope for defect-induced T_c-depressions of about 30 K. As possible mechanisms for the observed T_c-degradation, a defect-induced metal-to-semiconductor transition, which may be caused by a change of the local stoichiometry, and electron localization are discussed