MICROSTRUCTURE OF CU-RICH AND Y-RICH YBA2CU3O7-X THIN-FILMS - IDENTIFICATION OF THE CUYO2 PHASE

The CuYO2 delafossite-type structure has been identified as a second phase in thin films of Cu- and Y-rich YBa2Cu3O 7-x (123) made by electron beam co-evaporation at conditions of low oxygen pressure; this phase occurs as extremely small, densely distributed, highly oriented precipitates within the 123 matrix. The smallest (sub-100 Å) [00.1] oriented precipitates of this hexagonal phase are strained to give a better lattice match to the surrounding 123 structure. The results suggest that, for thin film deposition conditions of sufficiently low temperature and pressure, there may be a tie line between YBa2Cu 3O7-x and CuYO2 in the equilibrium phase diagram. The size and distribution of the precipitates is such as would be expected to influence structurally sensitive superconducting transport properties.