Features of the twin structure of YBa2Cu3O7−x epitaxial films

X-ray diffraction is used to investigate YBa2Cu3O7−x (YBCO) films on NdGaO3(110) and a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $${{(100)CeO_2 } \mathord{\left/ {\vphantom {{(100)CeO_2 } {(1\bar 102)}}} \right. \kern-\nulldelimiterspace} {(1\bar 102)}}Al_2 O_3 $$ \end{document} heterostructure. Symmetric, asymmetric, and axial geometries for θ and θ/2θ scans are used to obtain diffraction spectra from different crystallographic planes. The orientational and quantitative twinning characteristics of the films are determined. While the crystallographic parameters of these two types of film (the films are c-axis oriented with c=11.67 Å) are similar, there are differences in the twin structure. In particular, the features of the NdGaO3 structure lead to the appearance of an angle differing from 90° (90.20°) between the possible (110) and θ/2θ twin planes in a YBCO film and a different number of twin components in each system of twins. It is concluded from an analysis of the broadening of reflections, which are sensitive to twinning, that there is not twinning in a 60% film of YBCO on Al2O3 with a CeO2 buffer layer.