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 (similar to 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. (c) 2006 American Institute of Physics.