Superconductive and normal-state transport properties of epitaxial YBa2(Cu1-xNix)3O7 films

Ni-doped epitaxial thin YBa2(Cu1-xNix)3O7-δ films have been prepared by high-oxygen-pressure dc sputtering from stoichiometric targets on SrTiO3 substrates. Structural properties of these c-axis-oriented films 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 Tc-depression rate changes to -1.5 K/(at. % Ni). A change in slope is also detectable in the dependence of the resistivity on Ni concentration. These results can be explained in a model based on a concentration-dependent site preference of the Ni atoms. The activation energy for vortex creep (extracted from resistive transitions) and the critical-current density show the pinning effectiveness of the dopant. Scaling laws for the pinning-force density have also been studied. The Hall concentration nH shows a slight increase for small x and a decrease for higher values. The slope dnH/dT is also lowered for increasing Ni content. Furthermore, the mobility and the Hall angle of the YBa2(Cu1-xNix)3O7-δ films were deduced from experimental data