CRYSTAL-STRUCTURE OF YBCO THIN-FILMS GROWN AT SUBSTRATE TEMPERATURES OF ABOUT 500-DEGREES-C

Nonsuperconducting YBCO thin films were prepared by laser deposition a t 500 degrees C. The crystal structure of the films measured by XRD se ems to be cubic: cr = b = 3.890 Angstrom, c = 3.867 Angstrom. From EDX analysis follows within an accuracy of 1-2% there is no stoichiometri c difference between this nonsuperconducting YBCO and the common 90 K superconductor especially regarding the oxygen content. An existing st ructural model of a simple cubic YBCO perovskite unit cell, however, d oes not sufficient represent the experimental results. We suggest a mo dified model which based on known defects of the common c-axis YBCO. T his model is discussed in consideration of detailed ED and HTREM inves tigations.