  Ferroelectric films usually have phase states and physical properties very
different from those of bulk ferroelectrics. Here we propose free-standing
ferroelectric-elastic multilayers as a bridge between these two material
systems. Using a nonlinear thermodynamic theory, we determine phase states of
such multilayers as a function of temperature, misfit strain, and volume
fraction fi of ferroelectric material. The numerical calculations performed for
two classical ferroelectrics - PbTiO3 and BaTiO3 - demonstrate that
polarization states of multilayers in the limiting cases fi -> 0 and fi -> 1
coincide with those of thin films and bulk crystals. At intermediate volume
fractions, however, the misfit strain-temperature phase diagrams of multilayers
differ greatly from those of epitaxial films. Remarkably, a ferroelectric phase
not existing in thin films and bulk crystals can be stabilized in BaTiO3
multilayers. Owing to additional tunable parameter and reduced clamping,
ferroelectric multilayers may be superior for a wide range of device
applications.
