Microstructure of Cu- and Y-rich YBa2Cu3O7−x thin films: Identification of the CuYO2 phase

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Abstract
The CuYO2 delafossite‐type structure has been identified as a second phase in thin films of Cu‐ and Y‐rich YBa2Cu3O7−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 YBa2Cu3O7−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.