Crystal structure of YBCO thin films grown at substrate temperatures of about 500°C

Nonsuperconducting YBCO thin films were prepared by laser deposition at 500°C. The crystal structure of the films measured by XRD seems to be cubic: a = b = 3.890Å, c = 3.867Å. From EDX analysis follows within an accuracy of 1-2% there is no stoichiometric difference between this nonsuperconducting YBCO and the common 90 K superconductor especially regarding the oxygen content. An existing structural model of a simple cubic YBCO perovskite unit cell, however, does not sufficient represent the experimental results. We suggest a modified model which based on known defects of the common c-axis YBCO. This model is discussed in consideration of detailed ED and HTREM investigations.