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

Large epitaxially grown YBa2Cu3O7-delta (YBCO) films (50 mm in diameter) we re prepared on MgO and CeO2-buffered r-cut sapphire (CbS) substrates, for w hich homogeneity in the microwave surface resistance (R-S) and the crystal structures were studied. An automated measurement system based on a sapphir e-loaded TE01 delta mode cavity resonator was used for investigating the po sitional dependence of the R-S at low temperatures. The positional dependen ce of the R-S appeared to be strongly correlated with that of the in-plane alignments of YBCO grains in each YBCO film, with low R-S observed at the p ositions where the full width at half maximum of the Phi -scan of (113) pea k appeared small. However, no such correlation was observed between the R-S 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 similar to0.01 Angs trom over the film area for both YBCO/CbS and YBCO/MgO, the homogeneity in the R-S still appeared correlated with that of the c-axis constant for YBCO /CbS. For YBCO/MgO, correlation between the R-S and the c-axis constant app eared less clear. Our results show that the in-plane orientation of YBCO gr ains is one of the most important structural factors to be controlled to re duce the R-S of YBCO films and to improve the homogeneity in the R-S of lar ge c-axis oriented YBCO films.