Chemical control of polar behavior in bicomponent short-period superlattices

Abstract

Using first-principles density functional calculations, we study the interplay of ferroelectricity and polar discontinuities in a range of 1--1 oxide superlattices, built out of ferroelectric and paraelectric components. Studies have been carried out for a varied choice of chemical composition of the components. We find that, when polar interfaces are present, the polar discontinuities induce off-centric movements in the ferroelectric layers, even though the ferroelectric is only one unit cell thick. The distortions yield nonswitchable polarizations, with magnitudes comparable to those of the corresponding bulk ferroelectrics. In contrast, in superlattices with no polar discontinuity at the interfaces, the off-centric movements in the ferroelectric layer are usually suppressed. The details of the behavior and functional properties are, however, found to be sensitive to epitaxial strain, rotational instabilities and second-order Jahn-Teller activity, and are therefore strongly influenced by the chemical composition of the paraelectric layer.