MICROWAVE SURFACE-RESISTANCE OF PLASMA-SPRAYED YBACUO THICK-FILMS ON LARGE-AREA METALLIC SUBSTRATES

The microwave surface resistance of YBaCuO thick films was measured us ing a demountable copper cavity operated at 3 GHz in the TE0.11 mode o ver 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-buff ered copper substrates by a low-pressure plasma-spraying technique com bined with a melt-reaction method. The area of the end plate was 177 C M2 and that of the cylinder wall was 396 CM2. The surface resistance w as obtained from the Q values measured before and after substituting e ither 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 coppe r 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.