Origin of reduced polarizations in short-period BaTiO3/SrTiO3 ferroelectric superlattices

We present an analysis of the polarization properties of BaTiO3/SrTiO3 superlattices using an effective Hamiltonian derived from first-principles calculations based on density-functional theory. We show that the hardening and modification of local soft modes at the interface environment is responsible for (a) the deviation of the interface structure from the bulk one and (b) the suppression of polarization in the short-period superlattices. The effect of this interfacial coupling is shown to be enhanced as the epitaxial strain becomes tensile. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3056388]