Application of synchrotron-based reciprocal-space mapping at a fixed angular position to identification of crystal symmetry of Bi₄Ti₃O₁₂ epitaxial thin films

The crystal structures of Bi₄Ti₃O₁₂ epitaxial films with thicknesses of 50 and 3 nm were investigated using synchrotron-based diffraction. Films with (100)/(010) orientations (i.e. a and b domains) were grown on TiO₂ (101) single crystals using metal-organic chemical vapor deposition. Synchrotron-based reciprocal-space mapping at a fixed angular position was applied to the determination of the crystal symmetry of the films. This method used a grazing-incidence geometry at a fixed azimuthal angle using 25 keV incident X-rays, which enabled the generation of a reciprocal-space map with a single X-ray exposure. The maps recorded about 120 and 30 diffraction spots from the 50 and 3 nm-thick samples, respectively. A two-dimensional 200 × 250 mm detector was used 133 mm downstream from the sample. The results revealed that both Bi₄Ti₃O₁₂ films had a B1a1 monoclinic structure or a lower crystal symmetry.