Study of correlation between the microstructure and phase inhomogeneities of Y-Ba-Cu-O epitaxial films and their DC and microwave properties

The influence of various kinds of structure and phase inhomogeneity on elec trical properties of YBCO thin films prepared by inverted cylindrical magne tron sputtering has been investigated. A simultaneous analysis of the chang es in the microstructure and electrical parameters has allowed us to define the contribution of each kind of inhomogeneity in the restriction of the f ilm's electrical parameters. It has been found that the transition temperat ure depends mainly on deviations of the c-axis lattice parameter from its o ptimum value, the critical current density depends mainly on the out of pla ne misorientation of the film domains and the microwave surface resistance depends mainly on the volume of the high-angle misoriented domains. By usin g atomic force and scanning tunnelling microscopy regions of YBCO films wit h modified properties around Cu-rich second phase particles were observed. It is suggested that superconducting properties of these regions are worse than the matrix due to Cu depletion. Usually the relative area of these inh omogeneities in our films is about 30% and can occupy up to 50% and, theref ore, mostly determines the electrical properties of films. It is suggested that the processes of cation disorder deforming the film lattice play an im portant role in formation of structure and phase inhomogeneities in YBCO th in films.