Ferroelectric properties of KNbO3/KTaO3 superlattices by atomic-level simulation

We use atomic-level simulation methods to determine the zero-temperature structure and properties of coherent KNbO3/KTaO3 superlattices. We find that the in-plane behavior is essentially bulk-like with an abrupt jump in the polarization at the interfaces. By contrast, the polarization in the modulation direction is continuous through the interfaces with the interior of the KTaO3 layers remaining polarized for modulation lengths of up to 160 unit cells. The zero-frequency dielectric constant in the modulation direction has a similar magnitude to that of KNbO3. An investigation of the switching behavior shows that for modulation lengths greater than 24 unit cells, each KNbO3 layer behaves essentially independently. For modulation lengths of less than 12 unit cells, the KNbO3 layers interact so strongly with each other that the superlattice essentially behaves as a single artificial structure. (C) 2001 American Institute of Physics.