Free-standing ferroelectric multilayers: Crossover from thin-film to bulk behavior

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 phi(p) of passive elastic material. The numerical calculations performed for two classical ferroelectrics-PbTiO3 and BaTiO3-demonstrate that polarization states of multilayers in the limiting cases phi(p)-> 1 and phi(p)-> 0 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. (C) 2011 American Institute of Physics. [doi:10.1063/1.3647585]