SUPERCONDUCTIVE AND NORMAL-STATE TRANSPORT-PROPERTIES OF EPITAXIAL YBA2(CU1-XNIX)3O7 FILMS

Ni-doped epitaxial thin YBa2(Cu1-xNix)3O7-delta films have been prepar ed by high-oxygen-pressure dc sputtering from stoichiometric targets o n SrTiO3 substrates. Structural properties of these c-axis-oriented fi lms were not affected by Ni doping up to x = 15%. Inductively measured transition temperatures show a decrease with a rate of -4.5 K/(at. % Ni) for Ni concentrations up to x = 4%. For higher Ni contents the T(c )-depression rate changes to -1.5 K/(at. % Ni). A change in slope is a lso detectable in the dependence of the resistivity on Ni concentratio n. These results can be explained in a model based on a concentration- dependent site preference of the Ni atoms. The activation energy for v ortex creep (extracted from resistive transitions) and the critical-cu rrent density show the pinning effectiveness of the dopant. Scaling la ws for the pinning-force density have also been studied. The Hall conc entration n(H) shows a slight increase for small x and a decrease for higher values. The slope dn(H)/dT is also lowered for increasing Ni co ntent. Furthermore, the mobility and the Hall angle of the YBa2(Cu1-xN ix)3O7-delta films were deduced from experimental data.