Epitaxial c-oriented YBCO films laser deposited onto 3 in diameter CeO2-buffered sapphire wafers and LaAlO3 cylinders as well as sputter deposited onto 2 in diameter LaAlO3 wafers were characterized by integral and spatially resolved measurements of the critical current density j(c) and the microwave surface resistance R-s, by microstructure investigations using optical and electron microscopy and by x-ray diffraction. Epitaxial misorientations of in-plane-rotated as well as of a-axis-oriented grains were found in amounts up to 10%. The in-plane rotation seriously degraded R-s while the a orientation mainly lowered j(c). Moreover, a degradation of R-s and of the microwave power handling could be clearly correlated with the density of microcracks occasionally found in YBCO films on sapphire. Inhomogeneities like a-axis-oriented grains were observed to 'disperse' microcracks, probably in favour of the electrical properties. The impact of further microstructure imperfections on R-s, in particular of the typical twin lamellae and their domains, is discussed in view of findings from transmission electron microscopy. [References: 34]

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