FEATURES OF THE TWIN STRUCTURE OF YBA2CU3O7-X EPITAXIAL-FILMS

X-ray diffraction is used to investigate YBa2Cu3O7-x (YBCO) films on N dGaO3(110) and a (100) CeO2/(1 (1) over bar 02) Al2O3, heterostructure . Symmetric, asymmetric, and axial geometries for theta and theta/2 th eta scans are used to obtain diffraction spectra from different crysta llographic planes. The orientational and quantitative twinning charact eristics of the films are determined. While the crystallographic param eters of these two types of film (the films are c-axis oriented with c = 11.67 Angstrom) are similar, there are differences in the twin stru cture. In particular, the features of the NdGaO3 structure lead to the appearance of an angle differing from 90 degrees (90.20 degrees) betw een the possible (110) and (110) twin planes in a YBCO film and a diff erent number of twin components in each system of twins. It is conclud ed from an analysis of the broadening of reflections, which are sensit ive to twinning, that there is not twinning in a 60% film of YBCO on A l2O3 With a CeO2 buffer layer. (C) 1998 American Institute of Physics.