On the role of Ag in improved YBa₂Cu₃O_7-δ flms

In the present paper, we report that (i) silver could also help in crystallization along the c-direction, as shown in high quality Ag-doped YBa₂Cu₃O_7-δ (YBCO) films prepared by both laser ablation and DC Magnetron sputtering. In the case of the c-oriented films on (100) SrTiO₃ and (100) LaAlO₃ substrates in the near surface region, from ion channeling analysis, we obtained χ_min=1.5% and χ_min=3.5%, respectively, better than the undoped films; (ii) some Ag was found to re-evaporate during the film deposition and the percentage of retained Ag was dependent on the deposition techniques (mainly the deposition time and temperature). By RBS and ion channeling analyses we have found that about 1 wt.% Ag remained in the laser ablated Ag-doped film prepared from a 3 wt. % Ag-YBCO target, and (iii) at least some retained Ag occupied substitution positions. Jc (77K) measured by the SQUID magnetometer for the laser ablated Ag-doped film was found to be enhanced by a factor of 2 in comparison with the undoped film. The Jc enhancement in Ag doped films may not totally come from the improvement of the in-plane alignment.