Strain-coupled ferroelectric polarization in BaTiO_3-CaTiO_3 superlattices

摘要

We report on growth and ferroelectric (FE) properties of superlattices (SLs) composed of the FE BaTiO_3 and the paraelectric CaTiO_3. Previous theories have predicted that the polarization in (BaTiO_3)n/(CaTiO_3)n SLs increases as the sublayer thickness (n) increases when the same strain state is maintained. However, our BaTiO_3/CaTiO_3 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/cm~2. We suggest that the strain coupling plays a more important role in FE properties than the electrostatic interlayer coupling based on constant dielectric permittivities.