Microwave and structural properties of largeYBa2Cu3O7-δ films: a study on the homogeneity

Abstract

Large epitaxially grown YBa2Cu3O7-δ(YBCO) films (50 mm in diameter) were prepared on MgO and CeO2-buffered r-cut sapphire (CbS) substrates, for which homogeneity inthe microwave surface resistance (RS) and the crystal structures werestudied. An automated measurement system based on a sapphire-loaded TE01δ mode cavity resonator was used for investigating thepositional dependence of the RS at low temperatures. The positionaldependence of the RS appeared to be strongly correlated with that of thein-plane alignments of YBCO grains in each YBCO film, with low RS observedat the positions where the full width at half maximum of the Φ-scan of(113) peak appeared small. However, no such correlation was observed betweenthe RS and the degree of the c-axis orientation of YBCO grains in eachYBCO film. With the difference in the c-axis constant as small as~0.01 Å over the film area for both YBCO/CbS and YBCO/MgO, thehomogeneity in the RS still appeared correlated with that of the c-axisconstant for YBCO/CbS. For YBCO/MgO, correlation between the RS and thec-axis constant appeared less clear. Our results show that the in-planeorientation of YBCO grains is one of the most important structural factors tobe controlled to reduce the RS of YBCO films and to improve the homogeneityin the RS of large c-axis oriented YBCO films.