Two new superstructures Ba₄Ti₅O₁₀ and Ba₄Ti₄O₁₁ in epitaxial barium titanate nanodomains determined by nanobeam electron diffraction and high-resolution transmission electron microscopy

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.

Keywords:

• HRTEM
• electron diffraction
• epitaxial
• oxide thin film
• microstructure analysis

Funding

This work was supported by the National Science Foundation under Awards NSF/CMMI NIRT-0709293, NSF/DMR-0821745.