Microwave Surface Resistance of Plasma-Sprayed YBaCuO Thick Films on Large-Area Metallic Substrates

The microwave surface resistance of YBaCuO thick films was measured using a demountable copper cavity operated at 3 GHz in the TE011 mode over a temperature range from 4.2 K to 300 K. The films were deposited onto end plates and cylinder walls of silver substrates or nickel-buffered copper substrates by a low-pressure plasma-spraying technique combined with a melt-reaction method. The area of the end plate was 177 cm2 and that of the cylinder wall was 396 cm2. The surface resistance was obtained from the Q values measured before and after substituting either the end plate or the cylinder wall for one covered with the film. The ratio of the surface resistance of the film to that of the copper was lower than 0.08 at 5.2 K and 0.65 at 77.3 K for the end plate and was 0.15 at 5.1 K and 1.91 at 77.3 K for the cylinder wall.