Microwave and structural properties of large YBa2Cu3O7-δ films: a study on the homogeneity

Large epitaxially grown YBa2Cu3O7-? (YBCO) films (50?mm in diameter) were prepared on MgO and CeO2-buffered r-cut sapphire (CbS) substrates, for which homogeneity in the microwave surface resistance (RS) and the crystal structures were studied. An automated measurement system based on a sapphire-loaded TE01? mode cavity resonator was used for investigating the positional dependence of the RS at low temperatures. The positional dependence of the RS appeared to be strongly correlated with that of the in-plane alignments of YBCO grains in each YBCO film, with low RS observed at the positions where the full width at half maximum of the ?-scan of (113) peak appeared small. However, no such correlation was observed between the RS and the degree of the c-axis orientation of YBCO grains in each YBCO film. With the difference in the c-axis constant as small as ~0.01???over the film area for both YBCO/CbS and YBCO/MgO, the homogeneity in the RS still appeared correlated with that of the c-axis constant for YBCO/CbS. For YBCO/MgO, correlation between the RS and the c-axis constant appeared less clear. Our results show that the in-plane orientation of YBCO grains is one of the most important structural factors to be controlled to reduce the RS of YBCO films and to improve the homogeneity in the RS of large c-axis oriented YBCO films.

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