Microwave characteristics of Ag-doped YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films grown on MgO

We prepared the Ag-doped YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (Ag-YBCO) bulk pellets of undoped, 10 wt.%, and 20 wt% and grew high quality thin films on MgO (100) substrates from the pellet targets by pulsed laser deposition. The films are highly c-axis oriented with T/sub c//spl ap/85 K. At T=44 K, the observed critical current density, J/sub c/ was 2.70/spl times/10/sup 6/ A/cm/sup 2/ and 1.17/spl times/10/sup 6/ A/cm/sup 2/ for 10 wt.% and 20 wt.% Ag-YBCO films, respectively. The critical current density, J/sub c/, of the Ag-YBCO/MgO films was improved by 65% with Ag-doing with respect to that of the undoped film. Using meanderline microstrip resonators, we measured the low temperature microwave surface resistance, R/sub s/. The observed R/sub s/ value of the 20 wt.% Ag-YBCO film was as small as 0.71 m/spl Omega/ for at 36 K and 8 GHz. XRD and RBS analysis showed that no silver was in the Ag-YBCO films even for the largest composition of Ag (20 wt.%) in the target pellet.