  We report on growth and ferroelectric (FE) properties of superlattices (SLs)
composed of the FE BaTiO3 and the paraelectric (PE) 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, 2 show a FE polarization of ca. 8.5 uC/cm^2.
We suggest that the strain coupling plays more important role in FE properties
than the electrostatic interlayer coupling based on constant dielectric
permittivities.
