•Ermile Gaganidze1, Roland Heidinger1, Juergen
Halbritter1, Michael Lorenz2 und Holger Hochmuth2
1Forschungszentrum Karlsruhe, Institut fuer Materialforschung
I, Postfach 3640, 76021 Karlsruhe, Germany
2Universitaet Leipzig, Fakultaet fuer Physik und Geowissenschaften,
Institut fuer Experimentelle Physik II, Linnestr. 5, 04103 Leipzig, Germany
Ca ( £ 22 at %) substituting Y in YBa2Cu3O7-d
(YBCO) is well known to enhance the in-plane conductivity s(T
> Tc) and density of states nm and to enhance
the critical current density jcJ(T <
Tc) of bycristal boundaries. However, up to now no data
are available on microwave properties of epitaxial Ca-doped YBCO films.
Here first results are presented on large area PLD grown Y1-xCaxBa2Cu3O7-d
(Y1-xCaxBCO) films on 3-inch r-cut sapphire wafer
with a CeO2 buffer layer. The microwave surface resistance Rs(T,Hrf)
at 8.5 GHz of Ca substituted Y0.9Ca0.1BCO shows clear
reductions with respect to that of YBCO for temperatures below about 50
K up to the fields of 20 mT. Systematic studies and analysis of Rs(T
< Tc,Hrf) of 170 nm thin Y1-xCaxBCO
films with x =0; 0.1; 0.15 and 0.2 are presented. The separation of Rs
in intrinsic Rint and extrinsic rf residual losses Rres(T,Hrf)
and their field dependencies reveals a reduced mean free path l(T) due
to weak scattering at Ca in Rint(T), and an enforced strength
jcJ of natural weak links explainable by an enhanced nm
by additional hole doping by Ca.