Strain-coupled ferroelectric polarization in BaTiO3–CaTiO3 superlattices

We report on growth and ferroelectric (FE) properties of superlattices (SLs) composed of the FE BaTiO3 and the paraelectric CaTiO3. Previous theories have predicted that the polarization in (BaTiO3)n/(CaTiO3)n SLs increases as the sublayer thickness (n) increases when the same strain state is maintained. However, our BaTiO3/CaTiO3 SLs show a varying lattice-strain state and systematic reduction in polarization with increasing n while coherently strained SLs with n=1 and 2 show a FE polarization of ca. 8.5 μC/cm2. We suggest that the strain coupling plays a more important role in FE properties than the electrostatic interlayer coupling based on constant dielectric permittivities.