  Heterostructures consisting of PbZr0.2Ti0.8O3 and PbZr0.4Ti0.6O3 films grown
on a SrTiO3 (100) substrate with a SrRuO3 bottom electrode were prepared by
pulsed laser deposition. Using the additional interface provided by the
ferroelectric bilayer structure and changing the sequence of the layers, the
dislocation content and domain patterns were varied. The resulting
microstructure was investigated by transmission electron microscopy.
Macroscopic ferroelectric measurements have shown a large impact of the
formation of dislocations and the a/c domain structure on the ferroelectric
polarization and dielectric constant. A thermodynamic analysis using the
LANDAU-GINZBURG-DEVONSHIRE approach that takes into account the ratio of the
thicknesses of the two ferroelectric layers and electrostatic coupling is used
to describe the experimental data.
