Large-Area YBCO Films on Sapphire Substrates with Optimised Microwave Properties

In order to mechanically stabilise thick YBa2Cu3O7-x films on hf-suitable substrates with large lattice mismatch between substrate and high-Tc film, structural defects are introduced into the films. It is shown that the defects lead to an increase of the critical thickness of the films and a modified temperature dependence of the microwave surface reslstance, which can be explained in terms of d-wave superconductivity with a high defect density. The resulting surface resistance, hf power handling capability and intermodulation distortion are determined and seem to be improved by the presence of the defects.