MICROWAVE LOSSES AND STRUCTURAL-PROPERTIES OF LARGE-AREA YBA2CU3O7 FILMS ON R-CUT SAPPHIRE BUFFERED WITH (001) (111) ORIENTED CEO2/

YBa2Cu3O7-x thin films were prepared on 2 inch in diameter (1102) sapp hire substrates buffered with CeO2 layer of mixed (001)/(111) orientat ion. The thickness of the YBa2Cu3O7-x films was typically similar to 2 50 nm. The YBa2Cu3O7-x thin films exhibited smooth surfaces (peak-to-v alley roughness of less than 20 nm) free of cracks and outgrowths. The critical temperatures of these films were 87-89 K, the critical curre nt densities (2-3).10(6) A/cm(2) at 77 K and zero magnetic field. The low field microwave surface resistance (R-S) of the YBa2Cu3O7-x films was measured at 18.7 GHz. Values of similar to 1.4 m Omega were obtain ed at 77 K and <70 mu Omega below 20 K. Such low R-S values are compar able to the lowest reported values for thicker YBa2Cu3O7-x films grown epitaxially on structurally well-matched substrates, e.g. LaAlO3. The elevation of the microwave power produced a weak increase of R-S. No drastic changes in R-S occur up to the maximum magnetic field of simil ar to 35 Oe at 79 K and similar to 63 Oe at 50 K. The properties of th e YBa2Cu3O7-x films do not degrade with time.