Abstract
Barium titanate thin films deposited on MgO (0 0 1) by RF magnetron sputtering are composed of two new superstructures Ba4Ti5O10 and Ba4Ti4O11 formed as epitaxial nanodomain structures. Due to the nanometre scale size of domains and the complexity of the structure in the film, the single-crystal X-ray diffraction technique does not have the capability for the crystallographic structure determination of the two new superstructures. We used nanobeam electron diffraction to reconstruct the three-dimensional diffraction space and hence the symmetry of the new superstructures. Both Ba4Ti5O10 and Ba4Ti4O11 are monoclinic structures with a space group of Cm (b-unique axis). Ba4Ti5O10 has a lattice parameter a = 16.49 Å, b = 3.94 Å, c = 8.94 Å and β = 103°, while Ba4Ti4O11 has a = 17.88 Å, b = 3.94 Å, c = 7.21 Å and β = 98°. Atomic structural models for the two new superstructures were established by reconstructing the high-resolution transmission electron microscopy (HRTEM) images taken from the three major axes and refined by matching the simulated HRTEM images and calculated electron diffraction patterns with the experimental results. The two superstructures are epitaxially grown on MgO with their b-axis parallel to the growth direction.
Funding
This work was supported by the National Science Foundation under Awards NSF/CMMI NIRT-0709293, NSF/DMR-0821745.