Thermodynamic analysis and phase field modeling of domain structures in bilayer ferroelectric thin films

The domain structure in bilayer ferroelectric films was studied by using an analytical thermodynamic theory and computer simulations utilizing the phase field model. It is demonstrated that in a low applied field, a self-poled state can be produced in a bilayer film with one layer in a polydomain state and the other layer in a single-domain state. The presence of the layer with a polydomain structure results in a higher dielectric constant and lower coercive field as compared to a bilayer in a single-domain state. The increase in the applied field results in the transition to a single-domain state in the whole bilayer. The thermodynamic potentials of the layers and the energies of electrostatic and elastic interactions determine the critical fields which can control the transitions between single-domain and polydomain states as well as polarization switching of bilayers. Different thermodynamic hysteresis loops are obtained depending on the relationship between these critical fields and the amplitude of the applied ac field. The phase field model of the domain structure produces results that confirm main predictions of the analytical theory. (C) 2008 American Institute of Physics.