Structural evidence for enhanced polarization in a commensurate short-period BaTiO3∕SrTiO3 superlattice

A short-period (BaTiO3)6∕(SrTiO3)5 superlattice was characterized by x-ray diffraction and transmission electron microscopy. The superlattice is epitaxially oriented with the c axes of BaTiO3 and SrTiO3 normal to the (001) surface of the SrTiO3 substrate. Despite the large in-plane lattice mismatch between BaTiO3 and SrTiO3 (∼2.2%), the superlattice interfaces were found to be nearly commensurate. The crystallographic c∕a ratio of the superlattice was measured and the results agree quantitatively with first-principles calculations and phase-field modeling. The agreement supports the validity of the enhanced spontaneous polarization predicted for short-period BaTiO3∕SrTiO3 superlattices.