Twinning and domain structure of epitaxial YBa₂Cu ₃O_x films studies by X-ray diffraction methods

Structure, orientational features, and twinning of epitaxial superconductive YBa₂Cu₃O_x (YBCO) thin films and YBCO/CeO₂ heterostructures on (1 1 0) NdGaO₃ (NGO) and tilted-axes NdGaO₃ substrates with an inclination of normal of the substrate from the [1 1 0] axis were investigated by X-ray diffraction methods. Orthorhombic structure of NdGaO₃ results in an increase of the angle between (1 1 0) and (1 1 0) twinning planes in YBCO films to 90.20° and in a difference in volume of two twin domain systems. The orientation of epitaxial YBCO thin films was shown to be influenced by the deposition rate and the presence of symmetrical-equivalent directions [1 1 0] and [1 1 0] in the substrate and [1 0 0], [0 1 0], and [0 0 1] in the CeO₂ layer. Domain structure of the YBCO thin film changes with an increase in the inclination angle. The YBCO thin films on the tilted-axes substrates are twinned in the same way as on (1 1 0) NGO substrates. However, formation of one or both twinning complexes is suppressed with an increase of the inclination angle.