Orthorhombic strontium titanate in BaTiO₃–SrTiO₃superlattices

Abstract

It has been suggested by several authors that SrTiO 3 layers in SrTiO 3 -BaTiO 3 superlattices should be tetragonal and ferroelectric at ambient temperatures, like the BaTiO 3 layers, rather than cubic, as in bulk SrTiO 3 , and that freeenergy minimization requires continuity of the polarization direction. A recent ab initio calculation constrained solutions to this structure. Surprisingly, our x-ray study shows that the SrTiO 3 layers are orthorhombic with 0.03% in-plane strain, with the BaTiO 3 c-axis matching the SrTiO 3 a-and b-axis better than the c-axis; strain energy overcomes the cost in electrostatic energy.

Strain-coupled ferroelectric polarization in BaTiO3–CaTiO3 superlattices

“…In addition to the dielectric permittivity change and strain relaxation, one can also consider the possible crystallographic symmetry lowering that is also known to greatly influence the ferroelectric properties of ferroelectricparaelectric SLs. 33,34 However, we could not confirm such symmetry change in our SLs within the resolution of our in-house x-ray diffraction. It is also worthy to note that a recent first-principles study (Ref.…”

First-principles study of epitaxial strain in perovskites

“…As an example, this analysis has proved useful in the interpretation of first-principles results and experiments on the structure of partiallyrelaxed SrTiO 3 /BaTiO 3 superlattices. 26,27 First-principles information about the effects of epitaxial strain on the structure and polarization of component layers also allows us to determine the relative stability of a given superlattice. It is well known that lattice matching of the components minimizes the elastic energy and thus increases the stability.…”

Interfacial coherency and ferroelectricity of BaTiO3∕SrTiO3 superlattice films

“…It was reported that the relaxed ST/BT superlattices may possess symmetries lower than tetragonal. 6,7,10,11,14 However, the tetragonal symmetry in the BT layer is still retained with the polarization along the out-of-plane direction. It should be noted that the BT layers are still under an in-plane compressive strain even though the superlattice is fully relaxed with respective to the ST substrate.…”